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World history

Course: world history   >   unit 1.

  • History and prehistory
  • Prehistory before written records
  • Knowing prehistory

Homo sapiens and early human migration

  • Peopling the earth
  • Where did humans come from?
  • Paleolithic societies
  • Paleolithic technology, culture, and art
  • Organizing paleolithic societies
  • Paleolithic life
  • The origin of humans and early human societies
  • Homo sapiens , the first modern humans, evolved from their early hominid predecessors between 200,000 and 300,000 years ago. They developed a capacity for language about 50,000 years ago.
  • The first modern humans began moving outside of Africa starting about 70,000-100,000 years ago.
  • Humans are the only known species to have successfully populated, adapted to, and significantly altered a wide variety of land regions across the world, resulting in profound historical and environmental impacts.

Where do we begin?

Migration and the peopling of the earth, how and why, adaptation and effects on nature, what do you think, want to join the conversation.

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Good Answer

Introductory essay

Written by the educator who created What Makes Us Human?, a brief look at the key facts, tough questions and big ideas in his field. Begin this TED Study with a fascinating read that gives context and clarity to the material.

As a biological anthropologist, I never liked drawing sharp distinctions between human and non-human. Such boundaries make little evolutionary sense, as they ignore or grossly underestimate what we humans have in common with our ancestors and other primates. What's more, it's impossible to make sharp distinctions between human and non-human in the paleoanthropological record. Even with a time machine, we couldn't go back to identify one generation of humans and say that the previous generation contained none: one's biological parents, by definition, must be in the same species as their offspring. This notion of continuity is inherent to most evolutionary perspectives and it's reflected in the similarities (homologies) shared among very different species. As a result, I've always been more interested in what makes us similar to, not different from, non-humans.

Evolutionary research has clearly revealed that we share great biological continuity with others in the animal kingdom. Yet humans are truly unique in ways that have not only shaped our own evolution, but have altered the entire planet. Despite great continuity and similarity with our fellow primates, our biocultural evolution has produced significant, profound discontinuities in how we interact with each other and in our environment, where no precedent exists in other animals. Although we share similar underlying evolved traits with other species, we also display uses of those traits that are so novel and extraordinary that they often make us forget about our commonalities. Preparing a twig to fish for termites may seem comparable to preparing a stone to produce a sharp flake—but landing on the moon and being able to return to tell the story is truly out of this non-human world.

Humans are the sole hominin species in existence today. Thus, it's easier than it would have been in the ancient past to distinguish ourselves from our closest living relatives in the animal kingdom. Primatologists such as Jane Goodall and Frans de Waal, however, continue to clarify why the lines dividing human from non-human aren't as distinct as we might think. Goodall's classic observations of chimpanzee behaviors like tool use, warfare and even cannibalism demolished once-cherished views of what separates us from other primates. de Waal has done exceptional work illustrating some continuity in reciprocity and fairness, and in empathy and compassion, with other species. With evolution, it seems, we are always standing on the shoulders of others, our common ancestors.

Primatology—the study of living primates—is only one of several approaches that biological anthropologists use to understand what makes us human. Two others, paleoanthropology (which studies human origins through the fossil record) and molecular anthropology (which studies human origins through genetic analysis), also yield some surprising insights about our hominin relatives. For example, Zeresenay Alemsegad's painstaking field work and analysis of Selam, a 3.3 million-year old fossil of a 3-year-old australopithecine infant from Ethiopia, exemplifies how paleoanthropologists can blur boundaries between living humans and apes.

Selam, if alive today, would not be confused with a three-year-old human—but neither would we mistake her for a living ape. Selam's chimpanzee-like hyoid bone suggests a more ape-like form of vocal communication, rather than human language capability. Overall, she would look chimp-like in many respects—until she walked past you on two feet. In addition, based on Selam's brain development, Alemseged theorizes that Selam and her contemporaries experienced a human-like extended childhood with a complex social organization.

Fast-forward to the time when Neanderthals lived, about 130,000 – 30,000 years ago, and most paleoanthropologists would agree that language capacity among the Neanderthals was far more human-like than ape-like; in the Neanderthal fossil record, hyoids and other possible evidence of language can be found. Moreover, paleogeneticist Svante Pääbo's groundbreaking research in molecular anthropology strongly suggests that Neanderthals interbred with modern humans. Paabo's work informs our genetic understanding of relationships to ancient hominins in ways that one could hardly imagine not long ago—by extracting and comparing DNA from fossils comprised largely of rock in the shape of bones and teeth—and emphasizes the great biological continuity we see, not only within our own species, but with other hominins sometimes classified as different species.

Though genetics has made truly astounding and vital contributions toward biological anthropology by this work, it's important to acknowledge the equally pivotal role paleoanthropology continues to play in its tandem effort to flesh out humanity's roots. Paleoanthropologists like Alemsegad draw on every available source of information to both physically reconstruct hominin bodies and, perhaps more importantly, develop our understanding of how they may have lived, communicated, sustained themselves, and interacted with their environment and with each other. The work of Pääbo and others in his field offers powerful affirmations of paleoanthropological studies that have long investigated the contributions of Neanderthals and other hominins to the lineage of modern humans. Importantly, without paleoanthropology, the continued discovery and recovery of fossil specimens to later undergo genetic analysis would be greatly diminished.

Molecular anthropology and paleoanthropology, though often at odds with each other in the past regarding modern human evolution, now seem to be working together to chip away at theories that portray Neanderthals as inferior offshoots of humanity. Molecular anthropologists and paleoanthropologists also concur that that human evolution did not occur in ladder-like form, with one species leading to the next. Instead, the fossil evidence clearly reveals an evolutionary bush, with numerous hominin species existing at the same time and interacting through migration, some leading to modern humans and others going extinct.

Molecular anthropologist Spencer Wells uses DNA analysis to understand how our biological diversity correlates with ancient migration patterns from Africa into other continents. The study of our genetic evolution reveals that as humans migrated from Africa to all continents of the globe, they developed biological and cultural adaptations that allowed for survival in a variety of new environments. One example is skin color. Biological anthropologist Nina Jablonski uses satellite data to investigate the evolution of skin color, an aspect of human biological variation carrying tremendous social consequences. Jablonski underscores the importance of trying to understand skin color as a single trait affected by natural selection with its own evolutionary history and pressures, not as a tool to grouping humans into artificial races.

For Pääbo, Wells, Jablonski and others, technology affords the chance to investigate our origins in exciting new ways, adding pieces into the human puzzle at a record pace. At the same time, our technologies may well be changing who we are as a species and propelling us into an era of "neo-evolution."

Increasingly over time, human adaptations have been less related to predators, resources, or natural disasters, and more related to environmental and social pressures produced by other humans. Indeed, biological anthropologists have no choice but to consider the cultural components related to human evolutionary changes over time. Hominins have been constructing their own niches for a very long time, and when we make significant changes (such as agricultural subsistence), we must adapt to those changes. Classic examples of this include increases in sickle-cell anemia in new malarial environments, and greater lactose tolerance in regions with a long history of dairy farming.

Today we can, in some ways, evolve ourselves. We can enact biological change through genetic engineering, which operates at an astonishing pace in comparison to natural selection. Medical ethicist Harvey Fineberg calls this "neo-evolution". Fineberg goes beyond asking who we are as a species, to ask who we want to become and what genes we want our offspring to inherit. Depending on one's point of view, the future he envisions is both tantalizing and frightening: to some, it shows the promise of science to eradicate genetic abnormalities, while for others it raises the specter of eugenics. It's also worth remembering that while we may have the potential to influence certain genetic predispositions, changes in genotypes do not guarantee the desired results. Environmental and social pressures like pollution, nutrition or discrimination can trigger "epigenetic" changes which can turn genes on or off, or make them less or more active. This is important to factor in as we consider possible medical benefits from efforts in self-directed evolution. We must also ask: In an era of human-engineered, rapid-rate neo-evolution, who decides what the new human blueprints should be?

Technology figures in our evolutionary future in other ways as well. According to anthropologist Amber Case, many of our modern technologies are changing us into cyborgs: our smart phones, tablets and other tools are "exogenous components" that afford us astonishing and unsettling capabilities. They allow us to travel instantly through time and space and to create second, "digital selves" that represent our "analog selves" and interact with others in virtual environments. This has psychological implications for our analog selves that worry Case: a loss of mental reflection, the "ambient intimacy" of knowing that we can connect to anyone we want to at any time, and the "panic architecture" of managing endless information across multiple devices in virtual and real-world environments.

Despite her concerns, Case believes that our technological future is essentially positive. She suggests that at a fundamental level, much of this technology is focused on the basic concerns all humans share: who am I, where and how do I fit in, what do others think of me, who can I trust, who should I fear? Indeed, I would argue that we've evolved to be obsessed with what other humans are thinking—to be mind-readers in a sense—in a way that most would agree is uniquely human. For even though a baboon can assess those baboons it fears and those it can dominate, it cannot say something to a second baboon about a third baboon in order to trick that baboon into telling a fourth baboon to gang up on a fifth baboon. I think Facebook is a brilliant example of tapping into our evolved human psychology. We can have friends we've never met and let them know who we think we are—while we hope they like us and we try to assess what they're actually thinking and if they can be trusted. It's as if technology has provided an online supply of an addictive drug for a social mind evolved to crave that specific stimulant!

Yet our heightened concern for fairness in reciprocal relationships, in combination with our elevated sense of empathy and compassion, have led to something far greater than online chats: humanism itself. As Jane Goodall notes, chimps and baboons cannot rally together to save themselves from extinction; instead, they must rely on what she references as the "indomitable human spirit" to lessen harm done to the planet and all the living things that share it. As Goodall and other TED speakers in this course ask: will we use our highly evolved capabilities to secure a better future for ourselves and other species?

I hope those reading this essay, watching the TED Talks, and further exploring evolutionary perspectives on what makes us human, will view the continuities and discontinuities of our species as cause for celebration and less discrimination. Our social dependency and our prosocial need to identify ourselves, our friends, and our foes make us human. As a species, we clearly have major relationship problems, ranging from personal to global scales. Yet whenever we expand our levels of compassion and understanding, whenever we increase our feelings of empathy across cultural and even species boundaries, we benefit individually and as a species.

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essay on evolution of early humans

Zeresenay Alemseged

The search for humanity's roots, relevant talks.

essay on evolution of early humans

Spencer Wells

A family tree for humanity.

essay on evolution of early humans

Svante Pääbo

Dna clues to our inner neanderthal.

essay on evolution of early humans

Nina Jablonski

Skin color is an illusion.

essay on evolution of early humans

We are all cyborgs now

essay on evolution of early humans

Harvey Fineberg

Are we ready for neo-evolution.

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Frans de Waal

Moral behavior in animals.

essay on evolution of early humans

Jane Goodall

What separates us from chimpanzees.

Frontiers for Young Minds

Frontiers for Young Minds

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A Brief Account of Human Evolution for Young Minds

essay on evolution of early humans

Most of what we know about the origin of humans comes from the research of paleoanthropologists, scientists who study human fossils. Paleoanthropologists identify the sites where fossils can be found. They determine the age of fossils and describe the features of the bones and teeth discovered. Recently, paleoanthropologists have added genetic technology to test their hypotheses. In this article, we will tell you a little about prehistory, a period of time including pre-humans and humans and lasting about 10 million years. During the Prehistoric Period, events were not reported in writing. Most information on prehistory is obtained through studying fossils. Ten to twelve million years ago, primates divided into two branches, one included species leading to modern (current) humans and the other branch to the great apes that include gorillas, chimpanzees, bonobos, and orangutans. The branch leading to modern humans included several different species. When one of these species—known as the Neanderthals—inhabited Eurasia, they were not alone; Homo sapiens and other Homo species were also present in this region. All the other species of Homo have gone extinct, with the exception of Homo sapiens , our species, which gradually colonized the entire planet. About 12,000 years ago, during the Neolithic Period, some (but not all) populations of H. sapiens passed from a wandering lifestyle of hunting and gathering to one of sedentary farming, building villages and towns. They developed more complex social organizations and invented writing. This was the end of prehistory and the beginning of history.

What Is Evolution?

Evolution is the process by which living organisms evolve from earlier, more simple organisms. According to the scientist Charles Darwin (1809–1882), evolution depends on a process called natural selection. Natural selection results in the increased reproductive capacities of organisms that are best suited for the conditions in which they are living. Darwin’s theory was that organisms evolve as a result of many slight changes over the course of time. In this article, we will discuss evolution during pre-human times and human prehistory. During prehistory, writing was not yet developed. But much important information on prehistory is obtained through studies of the fossil record [ 1 ].

How Did Humans Evolve?

Primates, like humans, are mammals. Around ten to twelve million years ago, the ancestral primate lineage split through speciation from one common ancestor into two major groups. These two lineages evolved separately to become the variety of species we see today. Members of one group were the early version of what we know today as the great apes (gorillas, chimpanzees, and bonobos in Africa, orangutans in Asia) ( Figures 1 , 2 ); that is, the modern great apes evolved from this ancestral group. They mostly remained in forest with an arboreal lifestyle, meaning they live in trees. Great apes are also quadrupeds which means they move around with four legs on the ground (see Figure 2 ). The other group evolved in a different way. They became terrestrial, meaning they live on land and not in trees. From being quadrupeds they evolved to bipeds, meaning they move around on their two back legs. In addition the size of their brain increased. This is the group that, through evolution, gave rise to the modern current humans. Many fossils found in Africa are from the Australopithecus afarensis, Homo sapiens ."> genus named Australopithecus (which means southern ape). This genus is extinct, but fossil studies revealed interesting features about their adaptation toward a terrestrial lifestyle.

Figure 1 - Evolutionary scheme, showing that great apes and humans all evolved from a common ancestor.

  • Figure 1 - Evolutionary scheme, showing that great apes and humans all evolved from a common ancestor.
  • The Neanderthal picture is a statue designed from a fossil skeleton.

Figure 2 - Great Apes in nature.

  • Figure 2 - Great Apes in nature.
  • (above) Arboreal (in trees) locomotion of orangutans and (under) the quadrupedal (four-foot) locomotion of gorillas and chimpanzees.

Australopithecus afarensis and Lucy

In Ethiopia (East Africa) there is a site called Hadar, where several fossils of different animal species were found. Among those fossils was Australopithecus afarensis . In 1974, paleoanthropologists found an almost complete skeleton of one specimen of this species and named it Lucy, from The Beatles song “Lucy in the Sky with Diamonds.” The whole world found out about Lucy and she was in every newspaper: she became a global celebrity. This small female—only about 1.1 m tall—lived 3.2 million years ago. Analysis of her femurs (thigh bones) showed that she used terrestrial locomotion. Lucy could have used arboreal and bipedal locomotion as well, as foot bones of another A. afarensis individual had a curve similar to that found in the feet of modern humans [ 2 ]. Authors of this finding suggested accordingly that A. afarensis was exclusively bipedal and could have been a hunter-gatherer.

Homo habilis , Homo erectus , and Homo neanderthalensis

Homo is the genus (group of species) that includes modern humans, like us, and our most closely related extinct ancestors. Organisms that belong to the same species produce viable offspring. The famous paleoanthropologist named Louis Leakey, along with his team, discovered Homo habilis (meaning handy man) in 1964. Homo habilis was the most ancient species of Homo ever found [ 2 ]. Homo habilis appeared in Tanzania (East Africa) over 2.8 million years ago, and 1.5 million years ago became exinct. They were estimated to be about 1.40 meter tall and were terrestrial. They were different from Australopithecus because of the form of the skull. The shape was not piriform (pear-shaped), but spheroid (round), like the head of a modern human. Homo habilis made stone tools, a sign of creativity [ 3 ].

In Asia, in 1891, Eugene Dubois (also a paleoanthropologist) discovered the first fossil of Homo erectus (meaning upright man), which appeared 1.8 million years ago. This fossil received several names. The best known are Pithecanthropus (ape-man) and Sinanthropus (Chinese-man). Homo erectus appeared in East Africa and migrated to Asia, where they carved refined tools from stone [ 4 ]. Dubois also brought some shells of the time of H erectus from Java to Europe. Contemporary scientists studied these shells and found engravings that dated from 430,000 and 540,000 years ago. They concluded that H. erectus individuals were able to express themselves using symbols [ 5 ].

Several Homo species emerged following H. erectus and quite a few coexisted for some time. The best known one is Homo neanderthalensis ( Figure 3 ), usually called Neanderthals and they were known as the European branch originating from two lineages that diverged around 400,000 years ago, with the second branch (lineage) Homo sapiens known as the African branch. The first Neanderthal fossil, dated from around 430,000 years ago, was found in La Sima de los Huesos in Spain and is considered to originate from the common ancestor called Homo heidelbergensis [ 6 ]. Neanderthals used many of the natural resources in their environment: animals, plants, and minerals. Homo neanderthalensis hunted terrestrial and marine (ocean) animals, requiring a variety of weapons. Tens of thousands of stone tools from Neanderthal sites are exhibited in many museums. Neanderthals created paintings in the La Pasiega cave in the South of Spain and decorated their bodies with jewels and colored paint. Graves were found, which meant they held burial ceremonies.

Figure 3 - A comparison of the skulls of Homo sapiens (Human) (left) vs. Homo neanderthalensis (Neanderthal) (right).

  • Figure 3 - A comparison of the skulls of Homo sapiens (Human) (left) vs. Homo neanderthalensis (Neanderthal) (right).
  • You can see a shape difference. From Scientific American Vol. 25, No. 4, Autumn 2016 (modified).

Denisovans are a recent addition to the human tree. In 2010, the first specimen was discovered in the Denisova cave in south-western Siberia. Very little information is known on their behavior. They deserve further studies due to their interactions with Neandertals and other Homo species (see below) [ 7 ].

Homo sapiens

Fossils recently discovered in Morocco (North Africa) have added to the intense debate on the spread of H. sapiens after they originated 315,000 years ago [ 8 ]. The location of these fossils could mean that Homo sapiens had visited the whole of Africa. In the same way, the scattering of fossils out of Africa indicated their migrations to various continents [ 9 ]. While intensely debated, hypotheses focus on either a single dispersal or multiple dispersals out of the African continent [ 10 , 11 ]. Nevertheless, even if the origin of the migration to Europe is still a matter of debate [ 12 ], it appears that H. sapiens was present in Israel [ 13 ] 180,000 years ago. Therefore, it could be that migration to Europe was not directly from Africa but indirectly through a stay in Israel-Asia. They arrived about 45,000 years ago into Europe [ 14 ] where the Neanderthals were already present (see above). Studies of ancient DNA show that H. sapiens had babies with Neanderthals and Denisovans. Nowadays people living in Europe and Asia share between 1 and 4% of their DNA with either Neanderthals or Denisovans [ 15 ].

Several thousand years ago H. sapiens already made art, like for example the wall painting in the Chauvet cave (36,000 years ago) ( Figure 4 ) and the Lascaux cave (19,000 years ago), both in France. The quality of the paintings shows great artistic ability and intellectual development. Homo sapiens continued to prospect the Earth. They crossed the Bering Land Bridge, connecting Siberia and Alaska and moved south 12,500 years ago, to what is now called Chile. Homo sapiens gradually colonized our entire planet ( Figure 5 ).

Figure 4 - The lions in the Chauvet cave (−36,000 years).

  • Figure 4 - The lions in the Chauvet cave (−36,000 years).
  • In this period wild lions were present in Eurasia . Photo: Bradshaw foundation.com. Note the lively character of the picture.

Figure 5 - Homo sapiens traveled in the world at various periods as shown on the map.

  • Figure 5 - Homo sapiens traveled in the world at various periods as shown on the map.
  • They had only their legs to move!

The Neolithic Revolution

Neolithic Period means New Stone Age, due to the new stone technology that was developed during that time. The Neolithic Period started at the end of the glacial period 11,700 years ago. There was a change in the way humans lived during the Neolithic Period. Ruins found in Mesopotamia tell us early humans lived in populated villages. Due to the start of agriculture, most wandering hunter-gatherers became sedentary farmers. Instead of hunting dogs familiar with hunter-gatherers, farmers preferred sheepdogs [ 16 ]. In the Neolithic age, humans were farming and herding, keeping goats and sheep. Aurochs (extinct wild cattle), shown in the paintings from the Lascaux cave, are early ancestors of the domesticated cows we have today [ 17 ]. The first produce which early humans began to grow in Mesopotamia (a historical region in West Asia, situated between the Tigris and Euphrates rivers) was peas and wheat [ 18 ]. Animals and crops were traded and written records were kept of these trades. Clay tokens were the first money for these transactions. The Neolithic Period saw the creation of commerce, money, mathematics, and writing ( Figure 6 ) in Sumer, a region of Mesopotamia. The birth of writing started the period that we call “history,” in which events are written down and details of big events as well as daily life can easily be passed on. This tremendous change in human lifestyle can be called the Neolithic Revolution .

Figure 6 - From the beginning to final evolution of cuneiform writing.

  • Figure 6 - From the beginning to final evolution of cuneiform writing.
  • Writing on argil support showed changes from pictograms to abstract design. Picture modified from British Museum. Dates in year BC.

From the time of Homo erectus , Homo species migrated out of Africa. Homo sapiens extended this migration over the whole planet. In the fifteenth and sixteenth centuries, Europeans explored the world. On the various continents, explorers met unknown populations. The Europeans were wondering if those beings were humans or not. But actually, those populations were also descendants of the men and women who colonized the earth at the dawn of mankind. In much earlier times, there was a theory that there were several races of humans, based mostly on skin color, but this theory was not supported by science. Current studies of DNA show that more than seven billion people who live on earth today are not of different races. There is only one human species on earth today, named Homo sapiens .

Suggested Reading

Species and Speciation. What defines a species? How new species can arise from existing species. https://www.khanacademy.org/science/biology/her/tree-of-life/a/species-speciation

Speciation : ↑ The formation of new and distinct species in the course of evolution.

Genus : ↑ In the classification of biology, a genus is a subdivision of a family. This subdivision is a grouping of living organisms having one or more related similarities. In the binomial nomenclature, the universally used scientific name of each organism is composed of its genus (capitalized) and a species identifier (lower case), for example Australopithecus afarensis, Homo sapiens.

Eurasia : ↑ A term used to describe the combined continental landmass of Europe and Asia.

Clay : ↑ Fine-grained earth that can be molded when wet and that is dried and baked to make pottery.

Revolution : ↑ Fundamental change occurring relatively quickly in human society.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

The authors thank Emma Clayton (Frontiers) for her advice and careful reading. Photo of Neanderthal statue was from Stephane Louryan, one of the designers of Neanderthal’s statue project [Faculty of Medicine, Université libre de Bruxelles (ULB), Brussels, Belgium].

[1] ↑ Godfraind, T. 2016. Hominisation et Transhumanisme . Bruxelles: Académie Royale de Belgique.

[2] ↑ Ward, C. V., Kimbel, W. H., and Johanson, D. C. 2011. Complete fourth metatarsal and arches in the foot of Australopithecus afarensis. Science 331:750–3. doi: 10.1126/science.1201463

[3] ↑ Harmand, S., Lewis, J. E., Feibel, C. S., Lepre, C. J., Prat, S., Lenoble, A., et al. 2015. 3.3-million-year-old stone tools from Lomekwi 3, West Turkana, Kenya. Nature 521:310–5. doi: 10.1038/nature14464

[4] ↑ Carotenuto, F., Tsikaridze, N., Rook, L., Lordkipanidze, D., Longo, L., Condemi, S., et al. 2016. Venturing out safely: the biogeography of Homo erectus dispersal out of Africa. J. Hum. Evol. 95:1–12. doi: 10.1016/j.jhevol.2016.02.005

[5] ↑ Joordens, J. C., d’Errico, F., Wesselingh, F. P., Munro, S., de Vos, J., Wallinga, J., et al. 2015. Homo erectus at Trinil on Java used shells for tool production and engraving. Nature 518:228–31. doi: 10.1038/nature13962

[6] ↑ Arsuaga, J. L., Martinez, I., Arnold, L. J., Aranburu, A., Gracia-Tellez, A., Sharp, W. D., et al. 2014. Neandertal roots: cranial and chronological evidence from Sima de los Huesos. Science 344:1358–63. doi: 10.1126/science.1253958

[7] ↑ Vernot, B., Tucci, S., Kelso, J., Schraiber, J. G., Wolf, A. B., Gittelman, R. M., et al. 2016. Excavating Neandertal and Denisovan DNA from the genomes of Melanesian individuals. Science 352:235–9. doi: 10.1126/science.aad9416

[8] ↑ Richter, D., Grun, R., Joannes-Boyau, R., Steele, T. E., Amani, F., Rue, M., et al. 2017. The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age. Nature 546:293–6. doi: 10.1038/nature22335

[9] ↑ Vyas, D. N., Al-Meeri, A., and Mulligan, C. J. 2017. Testing support for the northern and southern dispersal routes out of Africa: an analysis of Levantine and southern Arabian populations. Am. J. Phys. Anthropol . 164:736–49. doi: 10.1002/ajpa.23312

[10] ↑ Reyes-Centeno, H., Hubbe, M., Hanihara, T., Stringer, C., and Harvati, K. 2015. Testing modern human out-of-Africa dispersal models and implications for modern human origins. J. Hum. Evol . 87:95–106. doi: 10.1016/j.jhevol.2015.06.008

[11] ↑ Templeton, A. 2002. Out of Africa again and again. Nature 416:45–51. doi: 10.1038/416045a

[12] ↑ Arnason, U. 2017. A phylogenetic view of the Out of Asia/Eurasia and Out of Africa hypotheses in the light of recent molecular and palaeontological finds. Gene 627:473–6. doi: 10.1016/j.gene.2017.07.006

[13] ↑ Callaway, E. 2018. Israeli fossils are the oldest modern humans ever found outside of Africa. Nature 554:15–6. doi: 10.1038/d41586-018-01261-5

[14] ↑ Benazzi, S., Douka, K., Fornai, C., Bauer, C. C., Kullmer, O., Svoboda, J., et al. 2011. Early dispersal of modern humans in Europe and implications for Neanderthal behaviour. Nature 479:525–8. doi: 10.1038/nature10617

[15] ↑ Vernot, B., and Akey, J. M. 2014. Resurrecting surviving Neandertal lineages from modern human genomes. Science 343:1017–21. doi: 10.1126/science.1245938

[16] ↑ Ollivier, M., Tresset, A., Frantz, L. A. F., Brehard, S., Balasescu, A., Mashkour, M., et al. 2018. Dogs accompanied humans during the Neolithic expansion into Europe. Biol. Lett. 14:20180286. doi: 10.1098/rsbl.2018.0286

[17] ↑ Gerling, C., Doppler, T., Heyd, V., Knipper, C., Kuhn, T., Lehmann, M. F., et al. 2017. High-resolution isotopic evidence of specialised cattle herding in the European Neolithic. PLoS ONE 12:e0180164. doi: 10.1371/journal.pone.0180164

[18] ↑ Revedin, A., Aranguren, B., Becattini, R., Longo, L., Marconi, E., Lippi, M. M., et al. 2010. Thirty thousand-year-old evidence of plant food processing. Proc. Natl. Acad. Sci. U.S.A . 107:18815–9. doi: 10.1073/pnas.1006993107

Science | February 2, 2021

An Evolutionary Timeline of Homo Sapiens

Scientists share the findings that helped them pinpoint key moments in the rise of our species

Skulls of Human Evolutionary History Mobile

Brian Handwerk

Science Correspondent

The long evolutionary journey that created modern humans began with a single step—or more accurately—with the ability to walk on two legs. One of our earliest-known ancestors, Sahelanthropus , began the slow transition from ape-like movement some six million years ago, but Homo sapiens wouldn’t show up for more than five million years. During that long interim, a menagerie of different human species lived, evolved and died out, intermingling and sometimes interbreeding along the way. As time went on, their bodies changed, as did their brains and their ability to think, as seen in their tools and technologies.

To understand how Homo sapiens eventually evolved from these older lineages of hominins, the group including modern humans and our closest extinct relatives and ancestors, scientists are unearthing ancient bones and stone tools, digging into our genes and recreating the changing environments that helped shape our ancestors’ world and guide their evolution.

These lines of evidence increasingly indicate that H. sapiens originated in Africa, although not necessarily in a single time and place. Instead it seems diverse groups of human ancestors lived in habitable regions around Africa, evolving physically and culturally in relative isolation, until climate driven changes to African landscapes spurred them to intermittently mix and swap everything from genes to tool techniques. Eventually, this process gave rise to the unique genetic makeup of modern humans.

“East Africa was a setting in foment—one conducive to migrations across Africa during the period when Homo sapiens arose,” says Rick Potts , director of the Smithsonian’s Human Origins Program. “It seems to have been an ideal setting for the mixing of genes from migrating populations widely spread across the continent. The implication is that the human genome arose in Africa. Everyone is African, and yet not from any one part of Africa.”

New discoveries are always adding key waypoints to the chart of our human journey. This timeline of Homo sapiens features some of the best evidence documenting how we evolved.

550,000 to 750,000 Years Ago: The Beginning of the Homo sapiens Lineage

Homo heidelbergensis

Genes, rather than fossils, can help us chart the migrations, movements and evolution of our own species—and those we descended from or interbred with over the ages.

The oldest-recovered DNA of an early human relative comes from Sima de los Huesos , the “Pit of Bones.” At the bottom of a cave in Spain’s Atapuerca Mountains scientists found thousands of teeth and bones from 28 different individuals who somehow ended up collected en masse. In 2016, scientists painstakingly teased out the partial genome from these 430,000-year-old remains to reveal that the humans in the pit are the oldest known Neanderthals , our very successful and most familiar close relatives. Scientists used the molecular clock to estimate how long it took to accumulate the differences between this oldest Neanderthal genome and that of modern humans, and the researchers suggest that a common ancestor lived sometime between 550,000 and 750,000 years ago.

Pinpoint dating isn't the strength of genetic analyses, as the 200,000-year margin of error shows. “In general, estimating ages with genetics is imprecise,” says Joshua Akey, who studies evolution of the human genome at Princeton University. “Genetics is really good at telling us qualitative things about the order of events, and relative time frames.” Before genetics, these divergence dates were estimated by the oldest fossils of various lineages scientists found. In the case of H. sapiens, known remains only date back some 300,000 years, so gene studies have located the divergence far more accurately on our evolutionary timeline than bones alone ever could.

Though our genes clearly show that modern humans, Neanderthals and Denisovans —a mysterious hominin species that left behind substantial traces in our DNA but, so far, only a handful of tooth and bone remains—do share a common ancestor, it’s not apparent who it was. Homo heidelbergensis , a species that existed from 200,000 to 700,000 years ago, is a popular candidate. It appears that the African family tree of this species leads to Homo sapiens while a European branch leads to Homo neanderthalensis and the Denisovans.

More ancient DNA could help provide a clearer picture, but finding it is no sure bet. Unfortunately, the cold, dry and stable conditions best for long-term preservation aren’t common in Africa, and few ancient African human genomes have been sequenced that are older than 10,000 years.

“We currently have no ancient DNA from Africa that even comes near the timeframes of our evolution—a process that is likely to have largely taken place between 800,000 and 300,000 years ago,” says Eleanor Scerri, an archaeological scientist at the Max Planck Institute for the Science of Human History in Germany.

300,000 Years Ago: Fossils Found of Oldest Homo sapiens

Homo Sapiens Skull Reconstruction

As the physical remains of actual ancient people, fossils tell us most about what they were like in life. But bones or teeth are still subject to a significant amount of interpretation. While human remains can survive after hundreds of thousands of years, scientists can’t always make sense of the wide range of morphological features they see to definitively classify the remains as Homo sapiens , or as different species of human relatives.

Fossils often boast a mixture of modern and primitive features, and those don’t evolve uniformly toward our modern anatomy. Instead, certain features seem to change in different places and times, suggesting separate clusters of anatomical evolution would have produced quite different looking people.

No scientists suggest that Homo sapiens first lived in what’s now Morocco, because so much early evidence for our species has been found in both South Africa and East Africa. But fragments of 300,000-year-old skulls, jaws, teeth and other fossils found at Jebel Irhoud , a rich site also home to advanced stone tools, are the oldest Homo sapiens remains yet found.

The remains of five individuals at Jebel Irhoud exhibit traits of a face that looks compellingly modern, mixed with other traits like an elongated brain case reminiscent of more archaic humans. The remains’ presence in the northwestern corner of Africa isn’t evidence of our origin point, but rather of how widely spread humans were across Africa even at this early date.

Other very old fossils often classified as early Homo sapiens come from Florisbad, South Africa (around 260,000 years old), and the Kibish Formation along Ethiopia’s Omo River (around 195,000 years old).

The 160,000-year-old skulls of two adults and a child at Herto, Ethiopia, were classified as the subspecies Homo sapiens idaltu because of slight morphological differences including larger size. But they are otherwise so similar to modern humans that some argue they aren’t a subspecies at all. A skull discovered at Ngaloba, Tanzania, also considered Homo sapiens , represents a 120,000-year-old individual with a mix of archaic traits and more modern aspects like smaller facial features and a further reduced brow.

Debate over the definition of which fossil remains represent modern humans, given these disparities, is common among experts. So much so that some seek to simplify the characterization by considering them part of a single, diverse group.

“The fact of the matter is that all fossils before about 40,000 to 100,000 years ago contain different combinations of so called archaic and modern features. It’s therefore impossible to pick and choose which of the older fossils are members of our lineage or evolutionary dead ends,” Scerri suggests. “The best model is currently one in which they are all early Homo sapiens , as their material culture also indicates.”

As Scerri references, African material culture shows a widespread shift some 300,000 years ago from clunky, handheld stone tools to the more refined blades and projectile points known as Middle Stone Age toolkits.

So when did fossils finally first show fully modern humans with all representative features? It’s not an easy answer. One skull (but only one of several) from Omo Kibish looks much like a modern human at 195,000 years old, while another found in Nigeria’s Iwo Eleru cave, appears very archaic, but is only 13,000 years old . These discrepancies illustrate that the process wasn’t linear, reaching some single point after which all people were modern humans.

300,000 Years Ago: Artifacts Show a Revolution in Tools

Stone Tools

Our ancestors used stone tools as long as 3.3 million years ago and by 1.75 million years ago they’d adopted the Acheulean culture , a suite of chunky handaxes and other cutting implements that remained in vogue for nearly 1.5 million years. As recently as 400,000 years ago, thrusting spears used during the hunt of large prey in what is now Germany were state of the art. But they could only be used up close, an obvious and sometimes dangerous limitation.

Even as they acquired the more modern anatomy seen in living humans, the ways our ancestors lived, and the tools they created, changed as well.

Humans took a leap in tool tech with the Middle Stone Age some 300,000 years ago by making those finely crafted tools with flaked points and attaching them to handles and spear shafts to greatly improve hunting prowess. Projectile points like those Potts and colleagues dated to 298,000 to 320,000 years old in southern Kenya were an innovation that suddenly made it possible to kill all manner of elusive or dangerous prey. “It ultimately changed how these earliest sapiens interacted with their ecosystems, and with other people,” says Potts.

Scrapers and awls, which could be used to work animal hides for clothing and to shave wood and other materials, appeared around this time. By at least 90,000 years ago barbed points made of bone— like those discovered at Katanda, Democratic Republic of the Congo —were used to spearfish

As with fossils, tool advancements appear in different places and times, suggesting that distinct groups of people evolved, and possibly later shared, these tool technologies. Those groups may include other humans who are not part of our own lineage.

Last year a collection including sophisticated stone blades was discovered near Chennai, India , and dated to at least 250,000 years ago. The presence of this toolkit in India so soon after modern humans appeared in Africa suggests that other species may have also invented them independently—or that some modern humans spread the technology by leaving Africa earlier than most current thinking suggests.

100,000 to 210,000 Years Ago: Fossils Show Homo sapiens Lived Outside of Africa

Skull From Qafzeh

Many genetic analyses tracing our roots back to Africa make it clear that Homo sapiens originated on that continent. But it appears that we had a tendency to wander from a much earlier era than scientists had previously suspected.

A jawbone found inside a collapsed cave on the slopes of Mount Carmel, Israel, reveals that modern humans dwelt there, alongside the Mediterranean, some 177,000 to 194,000 years ago. Not only are the jaw and teeth from Misliya Cave unambiguously similar to those seen in modern humans, they were found with sophisticated handaxes and flint tools.

Other finds in the region, including multiple individuals at Qafzeh, Israel, are dated later. They range from 100,000 to 130,000 years ago, suggesting a long presence for humans in the region. At Qafzeh, human remains were found with pieces of red ocher and ocher-stained tools in a site that has been interpreted as the oldest intentional human burial .

Among the limestone cave systems of southern China, more evidence has turned up from between 80,000 and 120,000 years ago. A 100,000-year-old jawbone, complete with a pair of teeth, from Zhirendong retains some archaic traits like a less prominent chin, but otherwise appears so modern that it may represent Homo sapiens . A cave at Daoxian yielded a surprising array of ancient teeth , barely distinguishable from our own, which suggest that Homo sapiens groups were already living very far from Africa from 80,000 to 120,000 years ago.

Even earlier migrations are possible; some believe evidence exists of humans reaching Europe as long as 210,000 years ago. While most early human finds spark some scholarly debate, few reach the level of the Apidima skull fragment, in southern Greece, which may be more than 200,000 years old and might possibly represent the earliest modern human fossil discovered outside of Africa. The site is steeped in controversy , however, with some scholars believing that the badly preserved remains look less those of our own species and more like Neanderthals, whose remains are found just a few feet away in the same cave. Others question the accuracy of the dating analysis undertaken at the site, which is tricky because the fossils have long since fallen out of the geological layers in which they were deposited.

While various groups of humans lived outside of Africa during this era, ultimately, they aren’t part of our own evolutionary story. Genetics can reveal which groups of people were our distant ancestors and which had descendants who eventually died out.

“Of course, there could be multiple out of Africa dispersals,” says Akey. “The question is whether they contributed ancestry to present day individuals and we can say pretty definitely now that they did not.”

50,000 to 60,000 Years Ago: Genes and Climate Reconstructions Show a Migration Out of Africa

Arabian Peninsula

All living non-Africans, from Europeans to Australia’s aboriginal people, can trace most of their ancestry to humans who were part of a landmark migration out of Africa beginning some 50,000 to 60,000 years ago , according to numerous genetic studies published in recent years. Reconstructions of climate suggest that lower sea levels created several advantageous periods for humans to leave Africa for the Arabian Peninsula and the Middle East, including one about 55,000 years ago.

“Just by looking at DNA from present day individuals we’ve been able to infer a pretty good outline of human history,” Akey says. “A group dispersed out of Africa maybe 50 to 60 thousand years ago, and then that group traveled around the world and eventually made it to all habitable places of the world.”

While earlier African emigres to the Middle East or China may have interbred with some of the more archaic hominids still living at that time, their lineage appears to have faded out or been overwhelmed by the later migration.

15,000 to 40,000 Years Ago: Genetics and Fossils Show Homo sapiens Became the Only Surviving Human Species

Homo floresiensis

For most of our history on this planet, Homo sapiens have not been the only humans. We coexisted, and as our genes make clear frequently interbred with various hominin species, including some we haven’t yet identified. But they dropped off, one by one, leaving our own species to represent all humanity. On an evolutionary timescale, some of these species vanished only recently.

On the Indonesian island of Flores, fossils evidence a curious and diminutive early human species nicknamed “hobbit.” Homo floresiensis appear to have been living until perhaps 50,000 years ago, but what happened to them is a mystery. They don’t appear to have any close relation to modern humans including the Rampasasa pygmy group, which lives in the same region today.

Neanderthals once stretched across Eurasia from Portugal and the British Isles to Siberia. As Homo sapiens became more prevalent across these areas the Neanderthals faded in their turn, being generally consigned to history by some 40,000 years ago. Some evidence suggests that a few die-hards might have held on in enclaves, like Gibraltar, until perhaps 29,000 years ago. Even today traces of them remain because modern humans carry Neanderthal DNA in their genome .

Our more mysterious cousins, the Denisovans, left behind so few identifiable fossils that scientists aren’t exactly sure what they looked like, or if they might have been more than one species. A recent study of human genomes in Papua New Guinea suggests that humans may have lived with and interbred with Denisovans there as recently as 15,000 years ago, though the claims are controversial. Their genetic legacy is more certain. Many living Asian people inherited perhaps 3 to 5 percent of their DNA from the Denisovans.

Despite the bits of genetic ancestry they contributed to living people, all of our close relatives eventually died out, leaving Homo sapiens as the only human species. Their extinctions add one more intriguing, perhaps unanswerable question to the story of our evolution—why were we the only humans to survive?

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Brian Handwerk | READ MORE

Brian Handwerk is a science correspondent based in Amherst, New Hampshire.

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Human Evolution

Six million years of human evolution.

Human evolution is the lengthy process of change by which people originated from apelike ancestors. Scientific evidence shows that the physical and behavioral traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years.

Paleoanthropology is the scientific study of human evolution which investigates the origin of the universal and defining traits of our species. The field involves an understanding of the similarities and differences between humans and other species in their genes, body form, physiology, and behavior. Paleoanthropologists search for the roots of human physical traits and behavior. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people.

What Can Human Fossils Tell Us?

Early human fossils and archeological remains offer the most important clues about this ancient past. These remains include bones, tools and any other evidence (such as footprints, evidence of hearths , or butchery marks on animal bones) left by earlier people. Usually, the remains were buried and preserved naturally. They are then found either on the surface (exposed by rain, rivers, and wind erosion) or by digging in the ground. By studying fossilized bones, scientists learn about the physical appearance of earlier humans and how it changed. Bone size, shape, and markings left by muscles tell us how those predecessors moved around, held tools, and how the size of their brains changed over a long time.

Archeological evidence refers to the things earlier people made and the places where scientists find them. By studying this type of evidence, archeologists can understand how early humans made and used  tools and lived in their environments.

Humans and Our Evolutionary Relatives

Humans are primates . Physical and genetic similarities show that the modern human species, Homo sapiens, has a very close relationship to another group of primate species, the apes. Modern humans and the great apes (large apes) of Africa – chimpanzees (including bonobos, or so-called “pygmy chimpanzees”) and gorillas – share a common ancestor that lived between 8 and 6 million years ago.

Humans first evolved in Africa, and much of human evolution occurred on that continent. The  fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa. Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, between 1.5 million and 1 million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years and to the Americas within the past 15,000 years or so.

Most scientists currently recognize some 15 to 20 different species of early humans. Scientists do not all agree, however, about how these species are related or which ones simply died out. Many early human species – certainly the majority of them – left no living descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species.

Human Characteristics

One of the earliest defining human traits, bipedalism – the ability to walk on two legs – evolved over 4 million years ago. Other important human characteristics – such as a large and complex brain, the ability to make and use tools, and the capacity for language  – developed more recently. Many advanced traits -- including complex symbolic expression, art , and elaborate cultural diversity – emerged mainly during the past 100,000 years. The beginnings of agriculture and the rise of the first civilizations occurred within the past 12,000 years.

Smithsonian Research Into Human Evolution

The Smithsonian’s Human Origins Program explores the universal human story at its broadest time scale. Smithsonian anthropologists research many aspects of human evolution around the globe, investigating fundamental questions about our evolutionary past, including the roots of human adaptability.

For example, Paleoanthropologist Dr. Rick Potts – who directs the Human Origins Program – co-directs ongoing research projects in southern and western Kenya and southern and northern China that compare evidence of early human behavior and environments from eastern Africa to eastern Asia. Rick’s work helps us understand the environmental changes that occurred during the times that many of the fundamental characteristics that make us human  - such as making tools and large brains – evolved, and that our ancestors were often able to persist through dramatic climate changes. Rick describes his work in the video Survivors of a Changing Environment .

Dr. Briana Pobiner is a Prehistoric Archaeologist whose research centers on the evolution of human diet (with a focus on meat-eating), but has included topics as diverse as cannibalism in the Cook Islands and chimpanzee carnivory. Her research has helped us understand that at the onset of human carnivory over 2.5 million years ago some of the meat our ancestors ate was scavenged from large carnivores, but by 1.5 million years ago they were getting access to some of the prime, juicy parts of large animal carcasses. She uses techniques similar to modern day forensics for her detective work on early human diets.

Paleoanthropologist Dr. Matt Tocheri conducts research into the evolutionary history and functional morphology of the human and great ape family, the Hominidae. His work on the wrist of Homo floresiensis , the so-called “hobbits” of human evolution discovered in Indonesia, received considerable attention worldwide after it was published in 2007 in the journal Science. He now co-directs research at Liang Bua on the island of Flores in Indonesia, the site where Homo floresiensis was first discovered.

Geologist Dr. Kay Behrensmeyer has been a long-time collaborator with Rick Potts’ human evolution research at the site of Olorgesailie in southern Kenya. Kay’s role with the research there is to help understand the environments of the sites at which evidence for early humans – in the form of stone tools as well as fossils of the early humans themselves – have been found, by looking at the sediments of the geological layers in which the artifacts and fossils have been excavated.

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  • Review Article
  • Published: 06 January 2021

The influence of evolutionary history on human health and disease

  • Mary Lauren Benton   ORCID: orcid.org/0000-0002-5485-1041 1 , 2 ,
  • Abin Abraham 3 , 4 ,
  • Abigail L. LaBella   ORCID: orcid.org/0000-0003-0068-6703 5 ,
  • Patrick Abbot 5 ,
  • Antonis Rokas   ORCID: orcid.org/0000-0002-7248-6551 1 , 3 , 5 &
  • John A. Capra   ORCID: orcid.org/0000-0001-9743-1795 1 , 5 , 6  

Nature Reviews Genetics volume  22 ,  pages 269–283 ( 2021 ) Cite this article

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  • Evolutionary genetics
  • Genetic variation
  • Medical genetics

Nearly all genetic variants that influence disease risk have human-specific origins; however, the systems they influence have ancient roots that often trace back to evolutionary events long before the origin of humans. Here, we review how advances in our understanding of the genetic architectures of diseases, recent human evolution and deep evolutionary history can help explain how and why humans in modern environments become ill. Human populations exhibit differences in the prevalence of many common and rare genetic diseases. These differences are largely the result of the diverse environmental, cultural, demographic and genetic histories of modern human populations. Synthesizing our growing knowledge of evolutionary history with genetic medicine, while accounting for environmental and social factors, will help to achieve the promise of personalized genomics and realize the potential hidden in an individual’s DNA sequence to guide clinical decisions. In short, precision medicine is fundamentally evolutionary medicine, and integration of evolutionary perspectives into the clinic will support the realization of its full potential.

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Introduction

Genetic disease is a necessary product of evolution (Box  1 ). Fundamental biological systems, such as DNA replication, transcription and translation, evolved very early in the history of life. Although these ancient evolutionary innovations gave rise to cellular life, they also created the potential for disease. Subsequent innovations along life’s long evolutionary history have similarly enabled both adaptation and the potential for dysfunction. Against this ancient background, young genetic variants specific to the human lineage interact with modern environments to produce human disease phenotypes. Consequently, the substrates for genetic disease in modern humans are often far older than the human lineage itself, but the genetic variants that cause them are usually unique to humans.

The advent of high-throughput genomic technologies has enabled the sequencing of the genomes of diverse species from across the tree of life 1 . Analysis of these genomes has, in turn, revealed the striking conservation of many of the molecular pathways that underlie the function of biological systems that are essential for cellular life 2 . The same technologies have also spearheaded a revolution in human genomics 3 ; currently, more than 120,000 individual whole human genome sequences are publicly available, and genome-scale data from hundreds of thousands more have been generated by consumer genomics companies 4 . Huge nationwide biobanks are also characterizing the genotypes and phenotypes of millions of people from around the world 5 , 6 , 7 . These studies are radically changing our understanding of the genetic architecture of disease 8 . It is also now possible to extract and sequence ancient DNA from remains of organisms that are thousands of years old, enabling scientists to reconstruct the history of recent human adaptation with unprecedented resolution 9 , 10 . These breakthroughs have revealed the recent, often complicated, history of our species and how it influences the genetic architecture of disease 8 , 11 . With the expansion of clinical whole-genome sequencing and personalized medicine, the influence of our evolutionary past and its implications for understanding human disease can no longer remain overlooked by medical practice; evolutionary perspectives must inform medicine 12 , 13 .

Much like a family’s medical history over generations, the genome is fundamentally a historical record. Decoding the evolution of the human genome provides valuable context for interpreting and modelling disease. This context is not limited to recent human evolution but also includes more ancient events that span life’s history. In this Review, we trace the 4 billion-year interplay between evolution and disease by illustrating how innovations during the course of life’s history have established the potential for, and inevitability of, disease. Beginning with events in the very deep past, where most genes and pathways involved in human disease originate, we explain how ancient biological systems, recent genetic variants and dynamic environments interact to produce both adaptation and disease risk in human populations. Given this scope, we cannot provide a comprehensive account of all evolutionary events relevant to human disease. Instead, our goal is to illustrate through examples the relevance of both deep and recent evolution to the study and treatment of genetic disease. Many of these key insights stem from recent discoveries, which have yet to be integrated into the broader canvas of evolutionary biomedicine (Box  2 ).

Box 1 The evolutionary necessity of disease

The definition of disease varies across biological, medical and evolutionary perspectives. Viewing disease through the lens of evolution provides a flexible and powerful framework for defining and classifying disease 12 . As illustrated in the reaction norms plotted in the figure, disease risk ( y axis) is a function of both genotype (coloured lines) and environment ( x axis).

Some genotypes lead to disease in all environments (line A); high-penetrance Mendelian disorders fall into this group. At the other extreme, disease risk may only occur in the case of a very specific pairing of environment and genotype (line D). Phenylketonuria (PKU), which manifests only in the presence of mutations that render both copies of the phenylalanine hydroxylase enzyme non-functional and a diet that includes phenylalanine, illustrates this case. Most diseases fall between these extremes (lines B and C). Disease often arises from fundamental evolutionary ‘mismatches’ between genotype and environment. For example, the high risk for obesity, a chronic disease with substantial heritability (30–40%) 177 , in many modern populations is due (at least in part) to rapid and recent changes in human lifestyle 178 , such as eating higher-calorie foods, maintaining more sedentary lifestyles and sleeping fewer hours. Here, obesity manifests due to a ‘mismatch’ between the genotype and a rapidly changing environment. Genotypes often have opposing effects on different traits. This evolutionary pattern, called antagonistic pleiotropy, often leads to disease 179 . A canonical example is balancing selection to maintain variation at the haemoglobin subunit-β ( HBB ) locus that protects against malarial disease but recessively leads to sickle cell anaemia. Antagonistic pleiotropy has also been detected in complex genetic traits, such as heart disease where alleles that increase lifetime reproductive success also increase the risk for heart disease 180 . As these examples illustrate, many modern human diseases exist because populations have not adapted to changing environments or previous adaptations lead to trade-offs between health and fitness. However, disease is not just a product of the modern world. As long as there is phenotypic variation, disease is inevitable; some individuals will be better suited to some environments (and thus healthier) than others.

essay on evolution of early humans

Box 2 Evolutionary medicine

Evolutionary medicine is the study of how evolutionary processes have produced human traits/disease and how evolutionary principles can be applied in medicine. This Review focuses on recent advances in evolutionary genomics as they relate to our understanding of the origins and genetic basis for disease. Evolutionary medicine is a larger field that has been extensively reviewed elsewhere 12 , 26 , 181 . For context, we introduce major principles of evolutionary medicine here. Evolutionary perspectives on medicine are predicated on the idea that human diseases emerge out of the constraints, trade-offs, mismatches and conflicts inherent to complex biological systems interacting (via natural selection) with diverse and shifting environments (Box  1 ).

Evolutionary medicine has identified several categories of explanation for complex genetic diseases. The first category of evolutionary explanation is that natural selection does not result in perfect bodies but operates on relative reproductive fitness constrained by the laws of physics and the role, availability and interactions of pre-existing biological variation that shapes or constrains the subsequent course of evolution 182 , 183 . A second explanation is mismatch between our biological legacy and our modern environments 184 . Mismatch between our biological adaptations to ancestral environments and modern lifestyles contributes to many common diseases, such as obesity, diabetes and heart disease, that are promoted by sedentary lifestyles and poor nutrition 185 , 186 . For example, past exposure to calorie-poor conditions may promote metabolically efficient ‘thrifty’ gene variants that may contribute to increased obesity in calorie-rich environments. A third explanation is that of trade-offs, the idea that there are combinations of traits that cannot be simultaneously optimized by natural selection 50 , 51 . The trade-off concept is related to evolutionary constraint, but encompasses a large set of phenomena that shape trait evolution. For example, many fitness-related traits draw on common energetic reserves, and investment in one comes at the expense of another 52 . Likewise, pleiotropic genetic variants that influence multiple systems create potential for trade-offs. Furthermore, symptoms that are interpreted as disease may actually represent conditionally adaptive responses. Finally, evolutionary conflicts provide a fourth possible explanation. All multicellular organisms are aggregates of genes and genomes with different evolutionary histories and with diverse strategic interests. This means that all traits expressed by complex metazoans are a balanced compromise between different genetic elements and bodily systems 187 . Pathology can emerge out of conflict when conditions perturb these compromises.

Macroevolutionary imprints on human disease

Systems involved in disease have ancient origins.

Many of cellular life’s essential biological systems and processes, such as DNA replication, transcription and translation, represent ancient evolutionary innovations shared by all living organisms. Although essential, each of these ancient innovations generated the conditions for modern disease (Fig.  1 ). In this section, we provide examples of how several ancient innovations have created substrates for dysfunction and disease, and how considering these histories contributes to understanding the biology of disease and extrapolating results from model systems to humans.

figure 1

A timeline of evolutionary events (top) in the deep evolutionary past and on the human lineage that are relevant to patterns of human disease risk (bottom). The ancient innovations on this timeline (left) formed biological systems that are essential, but are also foundations for disease. During recent human evolution (right), the development of new traits and recent rapid demographic and environmental changes have created the potential for mismatches between genotypes and modern environments that can cause disease. The timeline is schematic and not shown to scale. bya, billion years ago; kya, thousand years ago; mya, million years ago.

As a foundational (if obvious) example, the origin of self-replicating molecules 4 billion years ago formed the basis of life, but also the root of genetic diseases 12 , 14 , 15 . Similarly, asymmetric cell division may have evolved as an efficient way to handle cellular damage, but it also established the basis for ageing in multicellular organisms 16 , 17 . Myriad age-related diseases in humans, and many other multicellular organisms, are a manifestation of this first evolutionary trade-off .

The evolution of multicellularity, which has occurred many times across the tree of life, illustrates the interplay between evolutionary innovation and disease 18 . The origin of multicellularity enabled complex body plans with trillions of cells, involving innovations associated with the ability of cells to regulate their cell cycles, modulate their growth and form intricate networks of communication. But multicellularity also established the foundation for cancer 19 , 20 . Genes that regulate cell cycle control are often divided into two groups: caretakers and gatekeepers 21 , 22 . The caretakers are involved in basic control of the cell cycle and DNA repair, and mutations in these genes often lead to increased mutation rates or genomic instability, both of which increase cancer risk. Caretaker genes are enriched for functions with origins dating back to the first cells 23 . The gatekeepers appeared later, at the genesis of metazoan multicellularity 23 . The gatekeepers are directly linked to tumorigenesis through their roles in regulating cell growth, death and communication. The progression of individual tumours in a given patient is likewise informed by an evolutionary perspective. Designing treatments that account for the evolution of drug resistance and heterogeneity in tumours is a tenet of modern cancer therapy 24 , 25 , 26 , 27 , 28 , 29 .

Like multicellularity, the evolution of immune systems also set the stage for dysregulation and disease. Mammalian innate and adaptive immune systems are both ancient. Components of the innate immune system are present across metazoans and even some plants 30 , 31 , whereas the adaptive immune system is present across jawed vertebrates 32 . These systems provided molecular mechanisms for self-/non-self-recognition and response to pathogens, but they evolved in a piecemeal fashion, using many different, pre-existing genes and processes. For example, co-option of endogenous retroviruses provided novel regulatory elements for interferon response 33 . As well, it is clear that the human immune system has co-evolved with parasites, such as helminths, over millions of years. Helminth infection both induces and modulates an immune response in humans 34 .

Evolutionary analyses of development have revealed that new anatomical structures often arise by co-opting existing structures and molecular pathways that were established earlier in the history of life. For example, animal eyes, limb structure in tetrapods and pregnancy in mammals (Box  3 ) each evolved by adapting and integrating ancient genes and regulatory circuits in new ways 35 , 36 , 37 , 38 . This integration of novel traits into the existing network of biological systems gives rise to links between diverse traits via the shared genes that underlie their development and function 36 . As a result, many genes are pleiotropic — they have effects on multiple, seemingly unrelated, traits. We do not have space here to cover the full evolutionary scope of these innovations and their legacies, but just as in each of the cases described above, innovations and adaptations spanning from the origin of metazoans to modern human populations shape the substrate upon which disease appears.

Box 3 Pregnancy as a case study in evolutionary medicine

Mammalian pregnancy illustrates how consideration of a trait’s history across evolutionary time can inform our understanding of disease. Every human who ever lived experienced pregnancy, but its complexity is remarkable — it involves coordination between multiple genomes and physiological integration between individuals, and is administered by a transient organ, the placenta 188 . Furthermore, by ensuring the generational transmission of genetic information, it provides the substrate for all evolution and renewal of life itself 189 .

Macroevolutionary

Pregnancy in placental mammals, which appeared ~170 million years ago, involves physiological integration of fetal and maternal tissues via the placenta, a transient fetal-derived, extra-embryonic organ. Live birth and placentation open the door to interplay between mother and fetus over resource provisioning, with the potential for the mother to provide less than fetal demands because of other energetic needs, such as caring for other offspring. In some mammals, including humans, placentation is highly invasive, setting up a physiological tug of war between mother and fetus over provisioning. When this precarious balance is disrupted, diseases of pregnancy can occur. Poor maternal arterial remodelling during placentation limits placental invasion, which invokes a compensatory response by the distressed fetus. This imbalance results in inflammation, hypertension, kidney damage and proteinuria in the mother, and an increase in oxidative stress and spontaneous preterm birth in the fetus 190 . Pregnancy-associated maternal hypertension with proteinuria is clinically defined as pre-eclampsia with vascular aetiologies, with a poor prognosis for both mother and fetus if untreated. Understanding pre-eclampsia as the result of an evolutionary tug of war between mother and the fetus has medical implications 191 , 192 , 193 , 194 .

Human-specific

Timing of birth is key to a successful, healthy pregnancy, but little is known about the mechanisms governing the initiation of parturition. The steroid hormone progesterone and its receptors are involved in parturition in all viviparous species; however, how progesterone regulates parturition is likely to be species-specific. For example, the human progesterone receptor (PGR) exhibited rapid evolution after divergence from the last common ancestor with chimpanzees 195 , 196 . There are functional differences between the human and Neanderthal versions of the progesterone receptor 197 . The human-specific changes in the PGR influence its transcription and probably its phosphorylation 198 , 199 . Similarly, loci associated with human preterm birth have experienced diverse evolutionary forces, including balancing selection, positive selection and population differentiation 200 . The rapid and diverse types of evolutionary change observed in the PGR and some of the loci associated with preterm birth make it challenging to extrapolate analyses of their molecular functions in animal models, such as mice. In addition, humans and mice differ in reproductive strategies, morphology of the uterus, placentation, hormone production and the drivers of uterine activation 201 . For example, progesterone is produced maternally in mice throughout pregnancy, whereas in humans its production shifts to the placenta after the early stages of pregnancy. Given the unique evolutionary history of human pregnancy, many molecular aspects of pregnancy may be better studied in other model organisms or human cell-based systems.

Human population level

A central enigma of mammalian pregnancy is that the maternal immune system does not reject the foreign fetus; rather, it has not only evolved to accept the fetus but is also critical in the process of placentation 202 , 203 . The centrality of the maternal immune system in pregnancy has important medical implications. The modulation of the maternal immune system during pregnancy results in a lowered ability to clear certain infections 204 , 205 . Uterine natural killer (uNK) cells and their killer cell inhibitory receptors (KIRs) cooperate with fetal trophoblasts to regulate the maternal immune response. In addition, uNK cells are also involved in immune response to pathogens, and this dual role provides the substrate for evolutionary trade-offs. For example, the human-specific KIR AA haplotype is associated with lower birthweight and pre-eclampsia as well as with a more effective defence against Ebola virus and hepatitis 206 , 207 (Fig.  4a ). Modern human populations have variation in the diversity and identity of KIR haplotypes, probably due to selection on both placentation and host defence 208 . Infectious disease outbreaks, therefore, place a unique selective pressure on pregnancy. Severe outbreaks of infectious diseases, such as malaria, often produce significant shifts in population-level allele frequencies in pregnancy-related genes, such as FLT1 in malaria-endemic populations of Tanzania 209 . The varying pressures from infectious disease are likely to contribute to variation in risk of pregnancy-related diseases between modern populations.

Medical implications

Although ancient macroevolutionary innovations may seem far removed from modern human phenotypes, their imprint remains on the human body and genome. Understanding the constraints they impose can provide insight into mechanisms of disease.

Mapping the origins and evolution of traits and identifying the genetic networks that underlie them are critical to the accurate selection of model systems and extrapolation to human populations. Failure to consider the evolutionary history of homologous systems, their phylogenetic relationships and their functional contexts in different organisms can lead to inaccurate generalization. Instead, when considering a model system, key evolutionary questions about both the organism and the trait of interest can indicate how translatable the research will be to humans 39 , 40 . For example, is the similarity between the trait in humans and the trait in the model system due to shared ancestry, that is, homology ? The presence of homology in a human gene or system of study suggests potential as a model system; however, homology alone is not sufficient justification. Environmental and life history factors shape traits, and divergence between species complicates the simple assumption that homology provides genetic or mechanistic similarity. Thus, homology must be supplemented by understanding of whether the evolutionary divergence between humans and the proposed model led to functional divergence. For example, the rapid evolution of the placenta and variation in reproductive strategy across mammals have made it challenging to extrapolate results about the regulation of birth timing from model organisms, such as mouse, to humans (Box  3 ). More broadly, differences in genetic networks that underlie the development of homologous traits across mammals explain why the majority of successful animal trials fail to translate to human clinical trials 41 , 42 . Molecular mechanisms of ancient systems, such as DNA replication, can be studied using phylogenetically distant species; however, ‘humanizing’ these models to research human-specific aspects of traits may not be possible and comparative studies of closely related species may be required 40 .

Although evolutionary divergence in homologous traits is an impediment to the direct translation of findings from a model system to humans, understanding how these evolutionary differences came about can also yield insights into disease mechanisms. For example, intuition would suggest that large animals (many cells and cell divisions) with long lifespans (many ageing cells), such as elephants and whales, would be at increased risk for developing cancer. However, size and lifespan are not significantly correlated with cancer risk across species; despite their large size, elephants and whales do not have a higher risk of developing cancer 43 , 44 . Why is this so? Recent studies of the evolution of genes involved in the DNA damage response in elephants have revealed mechanisms that may contribute to cancer resistance. An ancient leukaemia inhibiting factor pseudogene ( LIF6 ) regained its function in the ancestor of modern elephants. This gene works in conjunction with the tumour suppressor gene TP53 , which has increased in copy number in elephants, to reduce elephants’ risk for cancer despite their large body size 45 , 46 . This illustrates a basic life history trade-off: selection has created mechanisms for cancer suppression and somatic maintenance in large vertebrates that are not needed in small short-lived vertebrates. Studying such seeming paradoxes, especially those with clear contrasts to human disease risk, will shed light on broader disease mechanisms and suggest targets for functional interventions with translation potential.

Human-specific evolution

Human adaptation, trade-offs and disease.

The macroevolutionary events described above created the foundation of genetic disease, but considering the more recent changes that occurred during the evolutionary history of the human lineage is necessary to illuminate the full context of human disease. Comparisons between humans and their closest living primate relatives, such as chimpanzees, have revealed diseases that either do not appear in other species or take very different courses 47 . We are beginning to understand the genetic differences underlying some of these human-specific conditions, with particular insights into infectious diseases.

The last common ancestors of humans and chimpanzees underwent a complex speciation event that is likely to have involved multiple rounds of gene flow between ~12 and 6 million years ago (mya) 48 . Over the millions of years after this divergence, climatic, demographic and social pressures drove the evolution of many physical and behavioural traits unique to the human lineage, including bipedalism (~7 mya), lack of body hair (~2–3 mya) and larger brain volume relative to body size (~2 mya) 12 , 47 . These traits evolved in a diverse array of hominin groups, mainly in Africa, although some of these species, such as Homo erectus , ventured into Europe and Asia.

These human adaptations developed on the substrate of tightly integrated systems shaped by billions of years of evolution, and thus beneficial adaptations with respect to one system often incurred trade-offs in the form of costs on other linked systems 49 . The trade-off concept derives from a branch of evolutionary biology known as life history theory. It is based on the observation that organisms contain combinations of traits that cannot be simultaneously optimized by natural selection 50 , 51 . For example, many fitness-related traits draw on common energetic reserves, and investment in one comes at the expense of another 52 . Large body size may improve survival in certain environments, but it comes at the expense of longer development and lower numerical investment in reproduction.

The trade-off concept is clinically relevant because it dispenses with the notion of a single ‘optimal’ phenotype or fitness state for an individual 49 , 53 , 54 . Given the interconnected deep evolution of the human body, many diseases are tightly linked, in the sense that decreasing the risk for one increases the risk for the other. Such diametric diseases and the trade-offs that produce them are the starkest when there is competition within the body for limited resources; for example, energy used for reproduction cannot be used for growth, immune function or other energy-consuming survival processes 54 . The molecular basis for diametric diseases often results from antagonistic pleiotropy at the genetic level — when a variant has contrasting effects on multiple bodily systems. In extreme cases, some diseases that manifest well after reproductive age, for example, Alzheimer disease, have been less visible to selection and, thus, potentially more susceptible to trade-offs. Cancer and neurodegenerative disorders also exhibit this diametric pattern, where cancer risk is inversely associated with Alzheimer disease, Parkinson disease and Huntington disease. This association is hypothesized to be mediated by differences in the neuronal energy use and trade-offs in cell proliferation and apoptosis pathways 49 . Similarly, osteoarthritis (breakdown of cartilage in joints often accompanied by high bone mineral density) and osteoporosis (low bone mineral density) rarely co-occur. Their diametric pattern reflects, at least in part, different probabilities across individuals of mesenchymal stem cells within bone marrow to develop into osteoblasts versus non-bone cells such as adipocytes 49 , 55 . In another example, a history of selection for a robust immune response can now lead to an increased risk for autoimmune and inflammatory diseases, especially when coupled with new environmental mismatches 49 , 54 . Other examples of trade-offs are found throughout the human body, manifesting in risk for diverse diseases, including psychiatric and rheumatoid disorders 49 , 56 .

Just as adaptations in deep evolutionary time created new substrates for disease, evolutionary pressures exerted on the human lineage established the foundation for complex cognitive capabilities, but they also established the potential for many neuropsychiatric or neurodevelopmental diseases. For example, genomic structural variants enabled functional innovation in the brain through the emergence of novel genes 57 , 58 , 59 , 60 . Many human-specific segmental duplications influence genes that are essential to the development of the human brain, such as SRGAP2C and ARHGAP11B . Both of these genes function in cortical development and may be involved in the expansion of human brain size 61 , 62 , 63 . The human-specific NOTCH2NL is also hypothesized to have evolved from a partial duplication event, and is implicated in increased output during human corticogenesis, another potential key contributor to human brain size 59 , 60 . Although these structural variants were probably adaptive 58 , they may have also predisposed humans to neuropsychiatric diseases and developmental disorders. Copy number variation in the region flanking ARHGAP11B , specifically a microdeletion at 15q13.3, is associated with risk for intellectual disability, autism spectrum disorder (ASD), schizophrenia and epilepsy 58 , 64 . Duplications and deletions of NOTCH2NL and surrounding regions are implicated in macrocephaly and ASD or microcephaly and schizophrenia, respectively 59 . These trade-offs also play out at the protein domain level. For example, the Olduvai domain (previously known as DUF1220) is a 1.4-kb sequence that appears in ~300 copies in the human genome; this domain has experienced a large human-specific increase in copy number. These domains appear in tandem arrays in neuroblastoma breakpoint family ( NBPF ) genes, and have been associated with both increased brain size and neuropsychiatric diseases, including autism and schizophrenia 65 . These examples suggest that the genomic organization of these human-specific duplications may have enabled human-specific changes in brain development while also increasing the likelihood of detrimental rearrangements that cause human disease 59 , 64 . Furthermore, genomic regions associated with neuropsychiatric diseases have experienced human-specific accelerated evolution and recent positive selection, providing additional evidence for the role of recent evolutionary pressures on human disease risk 66 , 67 . Schizophrenia-associated loci, for example, are enriched near human accelerated regions (HARs) that are conserved in non-human primates 68 . Variation in HARs has also been associated with risk for ASD, possibly through perturbations of gene regulatory architecture 69 .

Human immune systems have adapted in response to changes in environment and lifestyles over the past few million years; however, the rapid evolution of the immune system may have left humans vulnerable to certain diseases, such as HIV-1 infection. A similar virus, simian immunodeficiency virus (SIV), is found in chimpanzees and other primates, and studies in the early 2000s found evidence of AIDS-like symptoms (primarily a reduction in CD4 + T cells) in chimpanzees infected with SIV. Although the effects of SIV in chimpanzees mirror some of the effects of HIV in humans 70 , captive chimpanzees infected with HIV-1 do not typically develop AIDS and have better clinical outcomes. The differences in outcome are influenced by human-specific immune evolution. For example, humans have lost expression of several Siglecs, cell surface proteins that binds sialic acids, in T lymphocytes compared with great apes 71 . In support of this hypothesis, human T cells with high Siglec-5 expression survive longer after HIV-1 infection 72 . Moreover, there is a possible role for the rapidly evolving Siglecs in other diseases, such as epithelial cancers, that differentially affect humans relative to closely related primates 73 , 74 .

Another human-specific immune change is the deletion of an exon of CMP- N -acetylneuraminic acid hydroxylase ( CMAH ) leading to a difference in human cell surface sialoglycans compared with other great apes 75 , 76 , 77 . The change in human sialic acid to an N -acetylneuraminic acid (Neu5Ac) termination, rather than N -glycolylneuraminic acid (Neu5Gc), may have been driven by pressure to escape infection by Plasmodium reichenowi , a parasite that binds Neu5Gc and causes malaria in chimpanzees. Conversely, the prevalence of Neu5Ac probably made humans more susceptible to infection by the malaria parasite Plasmodium falciparum , which binds to Neu5Ac 78 , 79 , and another human-specific pathology: typhoid fever 80 . Typhoid toxin binds specifically and is cytotoxic to cells expressing Neu5Ac glycans. Thus, the deletion of CMAH was likely to have been selected for by pressure from pathogens, but has in turn enabled other human-specific diseases such as malaria and typhoid fever 81 . The rapid evolution of the human immune system creates the potential for human-specific disease. As a result, human-specific variation in many other human immune genes influences human-specific disease risk 82 , 83 .

These examples from recent human evolution highlight the ongoing interplay of genetic variation, adaptation and disease. Understanding the evolutionary history of traits along with the aetiology of related diseases can help identify and evaluate risks for unintended consequences of treatments due to trade-offs. For example, ovarian steroids have pleiotropic effects stimulating both bone growth and mitosis in breast tissues to mobilize calcium stores during lactation 54 . However, later in life this link gives rise to a clinical trade-off. Hormone replacement therapy in postmenopausal women reduces the risk for osteoporosis and ovarian cancer, but also, as a result of its effects on breast tissue, increases the risk for breast cancer. Given the commonality of the trade-off between maintenance and proliferation, this is just one of many examples of cancer risk emerging as a result of trade-offs in immune, reproductive and metabolic systems 56 , 84 . Pregnancy is also rife with clinically relevant trade-offs given the interaction between multiple individuals and genomes (mother, father and fetus) with different objectives (Box  3 ). Trade-offs at the cellular level also have medical implications. For example, cellular senescence is a necessary and beneficial part of many basic bodily responses, but the accumulation of senescent cells underlies many ageing-related disorders. Thus, individuals with different solutions to this trade-off may have very different ‘molecular’ versus ‘chronological’ ages 85 .

Identifying such trade-offs by studying disease and treatment response is of great interest, but is challenging for several reasons: the number of possible combinations of traits to consider is large; many humans must have experienced the negative effects; and data must be available on both traits in the same individuals. Here, evolution paired with massive electronic health record (EHR)-linked biobanks 5 , 86 , 87 provides a possible solution. By considering the evolutionary context and potential linkages between traits, the search space of possible trade-offs can be constrained. Then, diametric traits can be tested for among individuals in the EHRs by performing phenome-wide association studies (PheWAS) either on traits or genetic loci of interest and looking for inverse relationships 88 . The mechanisms underlying the observed associations could then be evaluated in model systems and, if validated, anticipated in future human treatments.

In addition to trade-offs, evolutionary analyses can help us identify therapeutic targets for uniquely human diseases. A small subset of humans infected with HIV never progress to AIDS — a resistance phenotype that has been generally attributed to host genomics 89 , 90 , 91 . Identifying and understanding the genes that contribute to non-progression is of great interest in the development of vaccines and treatments for HIV infection. Genome-wide association studies (GWAS) and functional studies have supported the role of the MHC class I region, specifically the HLA-B*27/B*57 molecules, in HIV non-progression 92 , 93 , 94 . Comparative genomics with chimpanzees identified a chimpanzee MHC class I molecule functionally analogous to that of the non-progressors that contains amino acid substitutions that change binding affinity for conserved areas of the HIV-1 and SIV viruses. Evolutionary analysis of this region suggests that these substitutions are the result of an ancient selective sweep in chimpanzee genomes that did not occur in humans 95 . This analysis not only helps us understand how humans are uniquely susceptible to HIV progression but also highlights functional variation in the MHC that are potential targets of medical intervention.

Recent human demographic history

Most genetic variants are young, but have diverse histories.

The complex demographic history of modern humans in the past 200,000 years has created differences in the genetic architecture of and risk for specific diseases among human populations. With genomic sequences of thousands of humans from diverse locations, we can compare genetic information over time and geography to better understand the origins and evolution of both individual genetic variants and human populations 96 , 97 , 98 . The vast majority of human genetic variants are not shared with other species 99 . Demographic events such as bottlenecks , introgression and population expansion shaped the genetic composition of human populations, whereas rapid introduction of humans into new environments and the subsequent adaptations created potential for evolutionary mismatches (Figs  2 , 3 ).

figure 2

Representative genes that have experienced local adaptive evolution over the past 100,000 years as humans moved across the globe. We focus on adaptations that also produced the potential for disease due to trade-offs or mismatches with modern environments. For each, we list the evolutionary pressure, the trait(s) influenced and the associated disease(s). The approximate regions where the adaptations occurred are indicated by blue circles. Arrows represent the expansion of human populations, and purple shading represents introgression events with archaic hominins. Supplementary Table S1 presents more details and references. COVID-19, coronavirus disease 2019; G6PD, glucose-6-phosphate dehydrogenase; UV, ultraviolet.

figure 3

Ancient human migrations, introgression events with other archaic hominins and recent population expansions have all contributed to the introduction of variants associated with human disease. Schematic of human evolutionary history, where the branches represent different human populations and the branch widths represent population size (top left). Letter labels refer to the processes illustrated in parts a – d . a | Human populations migrating out of Africa maintained only a subset of genetic diversity present in African populations. The resulting out-of-Africa bottleneck is likely to have increased the fraction of deleterious, disease-associated variants in non-African populations. Coloured circles represent different genetic variants. Circles marked with X denote deleterious, disease-associated variants. b | When anatomically modern humans left Africa, they encountered other archaic hominin populations. Haplotypes introduced by archaic introgression events (illustrated in grey) contained Neanderthal-derived variants (denoted by red circles) associated with increased disease risk in modern populations. c | In the last 10,000 years, the burden of rare disease-associated variants (denoted by yellow circles) has increased due to rapid population expansion. d | Modern human individuals with admixture in their recent ancestry, such as African Americans, can have differences in genetic risk for disease, because of each individual’s unique mix of genomic regions with African and European evolutionary ancestry. For example, each of the three admixed individuals depicted have the same proportions of African and European ancestry, but do not all carry the disease-associated variant found at higher frequency in European populations (illustrated by yellow circles). Summarizing clinical risk for a patient requires a higher resolution view of evolutionary ancestry along the genome and improved representation of genetic variation from diverse human populations.

Approximately 200,000 years ago, ‘ anatomically modern humans ’ (AMHs) first appeared in Africa. This group had the key physical characteristics of modern human groups and exhibited unique behavioural and cognitive abilities that enabled rapid improvements in tool development, art and material culture. Approximately 100,000 years ago, AMH groups began to migrate out of Africa. The populations ancestral to all modern Eurasians are likely to have left Africa tens of thousands of years later 98 , but quickly spread across Eurasia. Expansions into the Americas and further bottlenecks are thought to have occurred between 35,000 and 15,000 years ago. The details and uncertainties surrounding these origin and migration events are more extensively reviewed elsewhere 98 .

Populations that experience bottlenecks and founder effects have a higher mutation load than populations that do not, largely due to their lower effective population sizes reducing the efficacy of selection 100 (Fig.  3a ). During this dispersal, the migrant human populations harboured less genetic variation than was present in Africa. The reduction in diversity caused by the out-of-Africa and subsequent bottlenecks shaped the genetic landscape of all populations outside Africa.

AMHs did not live in isolation after migration out of Africa. Instead, there is evidence of multiple admixture events with other archaic hominin groups, namely Neanderthals and Denisovans 101 , 102 . Modern non-African populations derive approximately 2% of their ancestry from Neanderthals, with some Asian populations having an even higher proportion of archaic hominin ancestry (Fig.  3b ). African populations have only a small amount of Neanderthal and Denisovan ancestry, largely from back migration from European populations with archaic ancestry 103 . However, there is evidence of admixture with other, as yet unknown, archaic hominins in the genomes of modern African populations 104 , 105 , 106 .

Following their expansion around the globe, humans have experienced explosive growth over the past 10,000 years, in particular in modern Eurasian populations 107 , 108 (Fig.  3c ). Growth in population size modifies the genetic architecture of traits by increasing the efficacy of selection and generating many more low-frequency genetic variants. Although the impact of rare alleles is not completely understood, they often have a deleterious role in variation in traits in modern populations 109 . Although there is still debate about the combined effects of these recent demographic differences, a consensus is emerging that they are likely to have only minor effects on the efficacy of selection and the mutation load between human populations 100 , 110 , 111 , 112 , 113 , 114 . Nonetheless, there are substantial differences in allele frequency between populations that are relevant to disease risk 115 .

The exposure of humans to new environments and major lifestyle shifts, such as agriculture and urbanization, created the opportunity for adaptation 96 , 116 . Ancient DNA sequencing efforts coupled with recent statistical advances are beginning to enable the linking of human adaptations to specific environmental shifts in the recent past 96 , 117 , 118 . However, these rapid environmental changes also created new patterns of complex disease. Mismatch between our biological suitability for ancestral environments and modern environments accounts for the prevalence of many common diseases, such as obesity, diabetes or heart disease that derive from sedentary lifestyles and poor nutrition. The ancestral susceptibility model proposes that ancestral alleles that were adapted to ancient environments can, in modern populations, increase the risk for disease 119 , 120 . Supporting this hypothesis, both ancestral and derived alleles increase disease risk in modern humans 121 , 122 . However, underscoring the importance of recent demographic history, patterns of risk for ancestral and derived alleles differ in African and European populations, with ancestral risk alleles at higher frequencies in African populations 115 .

The different evolutionary histories of modern human individuals and populations described in the previous section influence disease susceptibilities and outcomes. Perhaps most striking are the mismatches and trade-offs resulting from recent immune system adaptations. Classic examples include genetic variants conferring resistance to malaria also causing sickle cell-related diseases in homozygotes 96 , 123 , or the predominantly African G1 and G2 variants in APOL1 protecting against trypanosomes and ‘sleeping sickness’ but leading to chronic kidney disease in individuals with these genotypes 96 . Similarly, a variant in CREBRF that is thought to have improved survival for people in times of starvation is now linked to obesity and type 2 diabetes 124 . In a study of ancient European populations, a variant in SLC22A4 , the ergothioneine transporter, that may have been selected for to protect against deficiency of ergothioneine (an antioxidant) is also associated with gastrointestinal problems such as coeliac disease, ulcerative colitis and irritable bowel syndrome 118 . The variant responsible did not reach high frequency in European populations until relatively recently, and current disease associations are likely to be new, perhaps as a result of mismatches with the current environment 118 . The possibility of mismatch is further supported by the varying prevalence of coeliac disease between human populations related to population-specific selection for several risk alleles 82 . Indeed, recent studies suggest that there is a relationship between ancestry and immune response, with individuals of African ancestry demonstrating stronger responses. This could be the result of selective processes in response to new environments for European populations, or a larger pathogen burden in Africa now leading to a higher instance of inflammatory and autoimmune disorders. This is still an open area of research, and more evidence is needed before strong conclusions can be drawn 125 .

In modern human environments, there is also a mismatch between the current low parasite infection levels and the immune system that evolved under higher parasite load. This mismatch is hypothesized to contribute to the increase in inflammatory and autoimmune diseases seen in modern humans 34 . For example, loci associated with ten different inflammatory diseases, including Crohn’s disease and multiple sclerosis, show evidence of selection consistent with the hygiene hypothesis 126 . Furthermore, recent positive selection on variants in the type 2 immune response pathway favoured alleles associated with susceptibility to asthma 127 . This suggests that recent evolutionary processes may have led to elevated or altered immune responses at the expense of increased susceptibility to inflammatory and autoimmune diseases. This insight has broad clinical implications, including the potential targeted use of helminths and natural products for immune modulation in patients with chronic inflammatory disease 128 , 129 .

Archaic introgression is relevant to modern medicine because alleles introduced by these evolutionary events continue to have an impact on modern populations even though the archaic hominin lineages are now extinct (Fig.  3b ). Archaic hominins had considerably lower effective population sizes than AMHs, and thus they probably carried a larger fraction of weakly deleterious mutations than AMHs 101 . As a result, Neanderthal introgression is predicted to have substantially increased the genetic load of non-African AMHs 130 , 131 . Large-scale sequencing efforts, in combination with analysis of clinical biobanks and improved computational methods, have revealed the potential impacts of introgressed DNA on modern human genomes. Several recent studies link regions of archaic admixture in modern populations with a range of diseases, including immunological, neuropsychiatric and dermatological phenotypes 102 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 . This demonstrates the functional impact of introgressed sequence on disease risk in non-African humans today. However, some of these associations may be influenced by linked non-Neanderthal alleles 140 . For example, in addition to alleles of Neanderthal origin, introgression also reintroduced ancestral alleles that were lost in modern Eurasian populations prior to interbreeding (for example, in the out-of-Africa bottleneck) 141 . Some introgressed alleles may have initially lessened adverse effects from migration to northern climates, dietary changes and introduction to novel pathogens 117 , 142 , 143 . For example, Neanderthal alleles contribute to variation in innate immune response across populations 125 , 132 , 134 , 144 and probably helped AMHs adapt to new viruses, in particular RNA viruses in Europe 145 . However, due to recent demographic and environmental changes, some previously adaptive Neanderthal alleles may no longer provide the same benefits 146 . For example, there is evidence that an introgressed Neanderthal haplotype increases risk for SARS-CoV-2 (ref. 147 ).

Physicians regularly rely on proxies for our more recent evolutionary history in the form of self-reported ancestry in their clinical practice; however, these measures fail to capture the complex evolutionary ancestry of each individual patient. For example, two individuals who identify as African Americans may both have 15% European ancestry, but this ancestry will be at different genomic loci and from different ancestral European and African populations (Fig.  3d ). Thus, one may carry a disease-increasing European ancestry allele whereas the other does not. Mapping fine-scale genetic ancestry across patients’ genomes can improve our ability to summarize clinically relevant risk 148 , but such approaches require broad sampling across populations and awareness of human diversity (Box  4 ). The profound need to increase the sampling of diverse groups is demonstrated by the lack of diversity in genomic studies, and the potential for health disparities caused by the over-representation of European-ancestry populations 149 , 150 , 151 (Fig.  4 ). In 2016, 81% of GWAS data were from studies conducted on European populations 149 . Although this is an improvement from 96% in 2009, most non-European populations still lack appropriate representation. The problem is more extreme for many phenotypes or traits of interest. For example, only 1.2% of the studies in a survey of 569 GWAS on neurological phenotypes included individuals of African ancestry 150 , 152 .

figure 4

a | Interactions between the maternal killer cell inhibitory receptor (KIR) genotype and the fetal trophoblasts illustrate evolutionary trade-offs in pregnancy. Birthweight is under stabilizing selection in human populations. The interaction between maternal KIR genotypes (a diversity of which are maintained in the population) and the fetal trophoblasts influence birthweight. African (AFR) populations, relative to European (EUR) populations, maintain larger proportions of the KIR AA haplotype 176 , which is associated with improved maternal immune response to some viral challenges; however, it is also associated with low birthweight. Alternatively, the KIR BB haplotype is associated with higher birthweight but increased risk of pre-eclampsia. b | Current strategies for predicting genetic risk are confounded by a lack of inclusion of diverse human populations. Thus, they are more likely to fail in genetic risk prediction in populations that are under-represented in genetic databases. For example, polygenic risk score (PRS) models trained on European populations often perform poorly when applied to African populations. This poor performance stems from the fact that the genetic diversity of African populations, differences in effect sizes between populations and differential evolutionary pressures are not taken into account. The weights for each variant (blue circles) in the PRS derived from genome-wide association studies are signified by w1, w2 and w3. c | Population-specific adaptation and genetic hitch-hiking can produce different disease risk between populations. Haplotypes with protective effects against disease may rise to high frequency in specific populations through genetic hitch-hiking with nearby alleles under selection for a different trait. For example, selection for lighter skin pigmentation caused a haplotype that carried a variant associated with lighter skin (blue circle) to increase in frequency in European populations compared with African populations. This haplotype also carried a variant protective against prostate cancer (blue triangle).

Ancestry biases in genomic databases and GWAS propagate through other strategies that are designed to translate population genetic insights to the clinic, such as polygenic risk scores (PRSs) 153 , 154 (Fig.  4b ). PRSs hold the promise of predicting medical outcomes from genomic data alone. However, the evolutionary perspective suggests that the genetic architecture of diseases should differ between populations due to the effects of the demographic and environmental differences discussed above. Indeed, many PRSs generalize poorly across populations and are subject to biases 155 , 156 . Prioritization of Mendelian disease genes is also challenging in under-represented populations. Generally, African-ancestry individuals have significantly more variants, yet we know less about the pathogenicity of variants that are absent from or less frequent in European populations 157 . Patients of African and Asian ancestry are currently more likely than those of European ancestry to receive ambiguous genetic test results after exome sequencing or be told that they have variants of uncertain significance (VUS) 158 . Indeed, disease-causing variants of African origin are under-represented in common databases 159 . This under-representation covers a range of phenotypic traits and outcomes, including interpreting the effects of CYP2D6 variants on drug response 160 , 161 , risk identification and classification for breast cancer across populations 162 , and disparate effects of GWAS associations for traits including body mass index (BMI) and type 2 diabetes in non-European populations 163 . In a study on hypertrophic cardiomyopathy, benign variants in African Americans were incorrectly classified as pathogenic on the basis of GWAS results from a European ancestry cohort. Inclusion of individuals of African descent in the initial GWAS could have prevented these errors 164 .

Box 4 Evolutionary medicine in clinical practice

Evolutionary perspectives have yet to be integrated into most areas of clinical practice. Notable exceptions involve diseases in which evolutionary processes act over short timescales to drive the progression of disease. For example, knowledge of the intense selective pressures underlying the evolution of drug resistance of microorganisms and the growth of tumours now guides the application of precise therapies and drug delivery strategies 210 , 211 , 212 , 213 . These examples illustrate how an evolutionary perspective can improve patient outcomes. However, they differ from the main focus of this article — the influence of human evolution on common genetic disease — where the relevant evolutionary processes have acted over thousands or millions of years.

Nonetheless, accounting for the innovations, adaptations and trade-offs that have shaped human populations should be considered in the clinical application of precision medicine to complex disease. For example, polygenic risk scores (PRSs) are a burgeoning technology with great clinical potential to stratify individuals by risk and enable preventative care 154 , 214 , but they have a fundamental dependence on underlying evolutionary processes. Individuals have different genetic backgrounds based on their ancestry, and these different histories alter the relationships between genotypes, environmental factors and risk of disease (Fig.  4 ). From this evolutionary perspective, PRSs should not be expected to generalize across populations and environments given the varied demographic histories of human populations that shape genetic variation 155 , 156 , 215 . Indeed, failure to account for this diversity in the application of PRSs and other genetics-based prediction methods can cause substantial harm and contribute to health disparities by producing misdiagnosis, improper drug dosing and inaccurate risk predictions 149 , 150 , 151 , 158 , 160 , 161 , 162 , 163 , 164 . An evolutionary approach is integral to solving this problem. PRSs must be developed and critically evaluated across the full range of human diversity to determine when genetic factors can provide an accurate risk profile for individuals. This is crucial in individuals with recent admixture in their ancestry, as risk profiles can vary based on the unique patterns of ancestry in each individual (Fig.  3 ). If genetic information is to inform personalized predictions about disease risk, explicitly considering evolution by quantifying genetic ancestry must be a critical component of this process.

The development of PRSs provides a timely and illustrative case study of how evolutionary perspectives can move from research contexts to inform clinical application. It also highlights the pitfalls of ignoring the implications of human evolutionary history when generalizing findings across populations. The establishment of a new technology (genome sequencing) enabled the measurement of a signal that is informative about disease risk (genetic variation) but is also influenced by evolutionary history. The knowledge gained from 100 years of basic research in population genetics about how human populations have evolved provides the context for these new technologies and the path towards ensuring that new treatments are not biased against specific populations.

Beyond providing context for existing analyses and treatments, new approaches are needed to translate our understanding of the history of human evolution from basic research to clinical relevance. In the main text, we highlight examples of how trade-offs, caused by competition for resources or antagonistic pleiotropy, may produce contrasting effects on disease risk within an individual. Similarly, new environmental conditions, such as a new pathogen, may rapidly create genetic mismatches in some populations. We propose that evolution-guided analysis of large-scale phenotype databases, such as those in electronic health record (EHR)-linked biobanks, are a promising approach for identifying novel patterns of diametric disease or mismatches in patient populations. For example, if a gene with pleiotropic functions is targeted by a treatment, such as a drug, knowledge of the gene’s evolution and functions can suggest specific phenotypes to test for diametric occurrence in the biobank. Given the overlapping evolutionary histories of molecular pathways involved in most traits, we anticipate that many clinically relevant trade-offs are waiting to be discovered.

Conclusions and future perspectives

All diseases have evolutionary histories, and the signatures of those histories are archived in our genomes. Recent advances in genomics are enabling us to read these histories with high accuracy, resolution and depth. Insights from evolutionary genomics reveal that there is not one answer to the question of why we get sick. Rather, diseases affect patchworks of ancient biological systems that evolved over millennia, and although the systems involved are ancient, the variation that is relevant for human disease is recent. Furthermore, evolutionary genomics approaches have the power to identify potential mechanisms, pathways and networks and to suggest clinical targets. In this context, we argue that an evolutionary perspective can aid the implementation of precision medicine in the era of genome sequencing and editing 165 (Box  4 ).

Combining knowledge of evolutionary events along the human lineage with results from recent genomic studies provides an explanatory framework beyond descriptions of disease risk or association. For example, a recent analysis of the higher incidence of prostate cancer among men of African ancestry not only discovered a set of genetic variants associated with increased risk, but also used measures of selection to propose an evolutionary explanation of genetic hitch-hiking for the lower incidence in non-African populations 166 . Haplotypes with protective effects against prostate cancer may have risen to higher frequency in non-African populations because of selection on the nearby variants associated with skin pigmentation (Fig.  4c ). Thus, evolutionary perspectives not only help answer the question of how we get sick but also why we get sick.

As the genetic information available from diverse populations increases, we can specifically map the genetics of traits in different populations and more precisely define disease risk on an individual basis 167 , 168 . However, we emphasize that environmental and social factors are major determinants of disease risk that often contribute more than genetics, and thus must be prioritized. Studying diverse human populations will provide additional power to discover trait-associated loci and understand genetic architecture across different environmental exposures and evolutionary histories 150 , 169 . For example, a GWAS with small sample size in a Greenlandic Inuit population found a variant in a fatty-acid enzyme that affects height in both this population and European populations 170 . Previous GWAS probably missed this variant due to its low frequency in European populations (0.017 compared with 0.98 in the Inuit); nevertheless, it has a much greater effect on height than other variants previously identified through GWAS 170 . Similarly, a recent study of height in 3,000 Peruvians identified another variant with an even greater influence on height 171 . The growth of large DNA biobanks in which hundreds of thousands of patients’ EHRs are linked to DNA samples represents a substantial untapped resource for evolutionary medicine 5 , 86 , 87 . These data enable testing of the functional effects of genetic variants on diverse traits at minimal additional cost. Shifting from single-ancestry GWAS to trans-ethnic or multi-ethnic GWAS will capitalize on the benefits of both a larger sample size and the inherent diversity of human populations for replication of established signals and discovery of new ones 172 , 173 , 174 , 175 .

Although evolutionary assumptions are tacit in medical practice, until recently self-reported family history remained the best representation of our evolutionary ancestry’s imprint on our disease risk. However, a family history cannot fully capture the complex evolutionary and demographic history of each individual. New technologies now enable the collection and interpretation of an individual’s family history in a much longer and complementary form — their genome. New data and methods are substantially increasing the resolution and depth with which these histories can be quantified, providing opportunities for evolution to inform medical practice.

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Acknowledgements

The authors thank L. Muglia and members of the Capra, Rokas and Abbot laboratories for helpful discussions. They also thank the National Institutes of Health (NIH) (T32LM012412 to M.L.B. and R35GM127087 to J.A.C.), the Burroughs Wellcome Fund Preterm Birth Initiative (A.R. and J.A.C.), the March of Dimes Prematurity Research Center Ohio Collaborative (P.A., A.R. and J.A.C.) and the American Heart Association (A.A.) for support.

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Supplementary table s1.

All aspects of the genetic variants that influence variation of a trait in a population. Commonly studied attributes of genetic architecture include the number of genetic loci that influence a trait, the frequency of these variants, the magnitudes of their effects and how they interact with one another and the environment. The genetic architectures of traits vary along these axes; for example, some traits are influenced by many common variants of small effect, whereas others are driven by a few rare variants of large effect.

Representations of how the expressed phenotype for a genotype varies in response to a range of environments. Reaction norms can be used to illustrate many of the concepts described in this Review, including evolutionary mismatches and antagonistic pleiotropy.

Adaptations that are advantageous for one phenotype have costs for others. Evolutionary trade-offs often result when genes influence multiple phenotypes (pleiotropy) or when there is a limited resource that must be apportioned to different functions. Because of trade-offs, there is not an optimal genotype across all environments.

Pertaining to pleiotropy, which is when a genetic locus (for example, a gene or regulatory element) has effects on multiple unrelated phenotypes. Antagonistic pleiotropy results when a locus has a beneficial effect on one trait and a detrimental effect on another.

Similarity in traits, bodily structures or genomic sequences due to shared ancestry between two species. Homology is considered when selecting model systems to study a particular phenotype; however, it does not guarantee underlying functional or mechanistic similarity.

Linked diseases for which decreasing the risk for one increases the risk for the other, such as protection from infectious disease increasing risk for autoimmune disease. Diametric disorders result from evolutionary trade-offs.

An animal that gives birth to live young, rather than laying eggs.

(HARs). Genomic loci conserved across mammalian species that experienced an increase in substitution rate specific to the human lineage. Genetic changes in HARs are responsible for some attributes of human-specific biology.

Rapid decreases in the size of populations that lead to a decrease in genetic diversity. Genetic bottlenecks can be caused by environmental factors (such as famine or disease) or demographic factors (such as migration). The ancestors of most modern non-African populations experienced a bottleneck as they left Africa, which is often referred to as the out-of-Africa bottleneck.

The flow of genetic material between two species through interbreeding followed by backcrossing. Analyses of ancient DNA have revealed that introgression was common in human history over the past several hundred thousand years.

(AMHs). Individuals, both modern and ancient, with the physical characteristics of humans ( Homo sapiens ) living today.

Reduced genetic diversity as a result of a small number of individuals establishing a new population from a larger original population. Founder effects can lead to genetic conditions that were rare in the original population becoming common in the new population. Serial founder effects occurred as anatomically modern humans spread out of Africa and colonized the world.

The component of the genetic load contributed by recent deleterious variants; other factors that contribute to the overall genetic load include the amount of heterozygote advantage and inbreeding.

The creation of novel genotypes from interbreeding between two genetically differentiated populations.

Ancient individuals on the human lineage, such as Neanderthals and Denisovans, that diverged before the origin of anatomically modern humans. Use of this terminology is established in human evolutionary genetics, but is not consistent across fields due to historical differences in the use of taxonomic terms and the fluidity of the species concept in the presence of substantial introgression.

A model proposing that ancestral alleles adapted to ancient environments can increase disease risk in modern environments due to evolutionary mismatches. Many human populations are likely to be subject to such mismatches due to rapidly changing environments.

A hypothesis proposing that immune systems adapted for environments with a high pathogen load are now mismatched to current environments with low pathogen load. This mismatch is further hypothesized to contribute to the higher incidence of autoimmune and inflammatory diseases.

The decrease in population fitness caused by the presence of non-optimal alleles compared with the most fit genotype: ( W max  –  W mean )  /  W max , where W max is the maximum possible fitness and W mean is the average fitness over all observed genotypes.

(PRSs). Results of a mathematical model to estimate the genetic risk of a disease for an individual based on the sum of the effects of all their genetic variants as estimated in a genome-wide association study. The clinical utility of PRSs is a topic of current debate (Box  4 ).

A disease caused by a variant in a single gene, such as sickle cell anaemia, cystic fibrosis and phenylketonuria. Mendelian (also known as monogenic) disorders are usually rare and follow simple dominant or recessive inheritance patterns.

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Benton, M.L., Abraham, A., LaBella, A.L. et al. The influence of evolutionary history on human health and disease. Nat Rev Genet 22 , 269–283 (2021). https://doi.org/10.1038/s41576-020-00305-9

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How scientists perceive the evolutionary origin of human traits: Results of a survey study

Hanna tuomisto.

1 Department of Biology, University of Turku, Turku, Finland

Matleena Tuomisto

Jouni t. tuomisto.

2 National Institute for Health and Welfare, Kuopio, Finland

Associated Data

Data are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.s9r98

Various hypotheses have been proposed for why the traits distinguishing humans from other primates originally evolved, and any given trait may have been explained both as an adaptation to different environments and as a result of demands from social organization or sexual selection. To find out how popular the different explanations are among scientists, we carried out an online survey among authors of recent scientific papers in journals covering relevant fields of science (paleoanthropology, paleontology, ecology, evolution, human biology). Some of the hypotheses were clearly more popular among the 1,266 respondents than others, but none was universally accepted or rejected. Even the most popular of the hypotheses were assessed “very likely” by <50% of the respondents, but many traits had 1–3 hypotheses that were found at least moderately likely by >70% of the respondents. An ordination of the hypotheses identified two strong gradients. Along one gradient, the hypotheses were sorted by their popularity, measured by the average credibility score given by the respondents. The second gradient separated all hypotheses postulating adaptation to swimming or diving into their own group. The average credibility scores given for different subgroups of the hypotheses were not related to respondent's age or number of publications authored. However, (paleo)anthropologists were more critical of all hypotheses, and much more critical of the water‐related ones, than were respondents representing other fields of expertise. Although most respondents did not find the water‐related hypotheses likely, only a small minority found them unscientific. The most popular hypotheses were based on inherent drivers; that is, they assumed the evolution of a trait to have been triggered by the prior emergence of another human‐specific behavioral or morphological trait, but opinions differed as to which of the traits came first.

1. INTRODUCTION

Human evolution is a topic that interests not just researchers specialized in paleoanthropology, but also other scientists and the general public. A number of conflicting hypotheses have been put forward to explain why humans have become strikingly different from other primates. Most scientists in relevant fields (such as paleoanthropology, paleontology, ecology, evolution and human biology) have never published their views on the drivers of human evolution in general, nor on which of the proposed hypotheses on the origin of specific human traits they find most substantiated. No recent summary of the mainstream view among paleoanthropologists has been published either, so there is uncertainty as to whether scientists agree on the driving forces behind human evolution or not. The idea of carrying out a survey to find out emerged when one of us was teaching a university course on human evolution, happened to check what Wikipedia had to say on the subject, and noticed that some Talk pages (especially the one behind the article “Aquatic ape hypothesis”) contained definite but unreferenced claims about what the opinions of “all scientists” or “all paleoanthropologists” are.

Humans differ from all the other 400 primate species in many respects, some of the most striking ones being that they walk fully upright on their hind legs, have unusually big brains, and have an effectively naked rather than fur‐covered skin (Figure  1 ). Other features that among primates are uniquely human include descended larynx, articulated speech and the capacity to accumulate fat in a thick subcutaneous layer.

An external file that holds a picture, illustration, etc.
Object name is ECE3-8-3518-g001.jpg

Male and female human figures from the plaque of the Pioneer 10 and 11 spacecrafts. The pictorial message was intended to describe the origin of the probe for potential extraterrestrial life. It shows several typically human traits, such as bipedalism, nakedness, arched nose, large head, and opposable thumbs. Source: NASA ; vectors by Mysid (Public domain), via Wikimedia Commons

A number of conflicting hypotheses have been proposed to explain why these and other traits originally evolved in the lineage leading to humans but in none of the lineages leading to other extant primates. One line of argumentation is based on the widely accepted idea that animal species adapt to their environment by natural selection: Traits that give the animal a higher probability of survival and reproduction become more common over time and traits related to lower survival and reproduction rates become less common. Adaptive traits are often morphological (like long legs that increase running speed and facilitate escaping from predators, or thick fur that protects from heat loss in cold weather), but they can also be behavioral (like building a nest or being nocturnal). The corollary of viewing traits of a species as adaptations to its environment is that traits are expected to change if the environment changes, because then also the adaptive pressures change. In particular, if sister species have very different traits in spite of close genetic relatedness, the adaptationist scenario suggests that the lineages experienced different environments during their evolutionary past.

It has indeed been proposed that the ancestors of humans came to live in a different kind of environment than the ancestors of chimpanzees and gorillas, and adapted by evolving a suite of novel traits. One of the early proposals along these lines, suggested already by Lamarck and Darwin, was that human ancestors descended from the trees and moved to the open savanna (Bender, Tobias, & Bender, 2012 ; Dart, 1925 ; Domínguez‐Rodrigo, 2014 ; Leakey & Lewin, 1977 ). Because terrestrial life in the dry savanna is very different from arboreal life in wet forests, this change in habitat would have shifted the prevailing selection pressures: Traits that were adaptive in the old environment could become maladaptive in the new one, and novel morphological traits could be favored if they gave a higher probability of survival and reproduction. The ancestors of the great apes stayed in the forest and, therefore, remained more similar to other primates.

The savanna scenario has lost some of its appeal since paleoenvironmental reconstructions started to show that the environmental setting has been more complex than was originally thought. Accordingly, more recent accounts describe the environment of early human ancestors as a mosaic of woodlands, savanna, and water bodies with considerable temporal fluctuations between climatically arid and wet periods (Bender et al., 2012 ; Domínguez‐Rodrigo, 2014 ; Kingston, 2007 ; Kovarovic & Andrews, 2007 ; Maslin & Christensen, 2007 ). Environmental variability itself has also been proposed to have selected for versatility of adaptations (Potts, 1998a , b ).

There have been different views on which aspects of terrestrial life would have required the morphological changes that the human lineage has experienced, so a large number of different explanations have been put forward for each trait. For example, the origin of the bipedal gait has been attributed to (among other things) gaining better visibility over the savanna grass (Ravey, 1978 ), reaching for food on low branches (Hunt, 1994 , 1996 ), collecting small food items from the ground (Jolly, 1970 ; Kingdon, 2003 ), exposing a smaller part of the body to the scorching sun (Wheeler, 1984 , 1991 ), allowing more energy‐efficient long‐distance travel (Carrier et al., 1984 ; Pontzer, Raichlen, & Sockol, 2009 ; Rodman & McHenry, 1980 ), and freeing the hands to carry food, tools, weapons, or babies (Bartholomew & Birdsell, 1953 ; Hewes, 1961 ; Lovejoy, 1981 ; Sutou, 2012 ; Washburn, 1960 ). It has also been proposed that bipedalism originated already in the trees for hand‐supported walking on small branches too weak for brachiation (Crompton, Sellers, & Thorpe, 2010 ; Thorpe, Holder, & Crompton, 2007 ).

Another adaptationist proposal is that the human ancestors moved from the trees to the waterside, and started to adapt to a partly aquatic way of life (Hardy, 1960 ; Morgan, 1982 ; Verhaegen, Puech, & Munro, 2002 ). This would have exposed them to similar selection pressures than semi‐aquatic mammals, rather than to selection pressures typically experienced by other primates. Under this scenario, bipedal gait would have emerged because it allowed wading to deeper water and made the body more streamlined when swimming and diving for food (Kuliukas, 2002 ; Morgan, 1990 ; Niemitz, 2010 ; Verhaegen et al., 2002 ).

Not all traits need to have originated to enhance survival, however, and critical voices have been raised against interpreting all uniquely human traits as adaptations driven by natural selection (Gee, 2013 ). Sexual selection is known to have produced spectacular new traits in various animals, typically ornaments whose sole purpose is to attract the attention of the opposite sex. These confer no survival advantage or may even be harmful to the bearer. At least human bipedalism, nakedness, and subcutaneous fat layer have been explained by this mechanism (Barber, 1995 ; Giles, 2011 ; Tanner, 1981 ). Especially in small populations, traits may even emerge due to chance fixation of random variation (Sutou, 2012 ).

For someone interested in the “why” of human evolution, it is currently hard to find a comprehensive account of the scientific state of the art. Journal articles typically address only one or a few hypotheses in isolation of the others and often their focus is more on “how” than on “why” a given trait originally emerged (e.g., Crompton et al., 2010 ; Cunnane & Crawford, 2014 ; Isler & Van Schaik, 2014 ; Stout & Chaminade, 2012 ; Watson, Payne, Chamberlain, Jones, & Sellers, 2008 ; Wells, 2006 ). Only proponents of the aquatic/waterside hypotheses (collectively known as the aquatic ape hypothesis or AAH) seem to maintain that it is possible to explain most of the uniquely human traits as adaptive responses to a specific external factor (e.g., Morgan, 1997 ; Vaneechoutte, Kuliukas, & Verhaegen, 2011 ), but these views have found little resonance in paleoanthropological journals (Bender et al., 2012 ). Indeed, AAH has been fiercely opposed and criticized for being an umbrella hypothesis that attempts to explain everything, for being unparsimonious, for lacking evidence and even for being pseudoscience (Hawks, 2005 ; Langdon, 1997 ; Moore, 2012 ).

Here, we aim to find out what scientists really think about why some of the most striking human traits have emerged. We do so by analyzing the results of an online survey where scientists were directly asked for their views on the issue.

2. MATERIALS AND METHODS

2.1. survey.

A survey was performed using an online form in early 2013. Invitation to participate in the survey was sent by email to the authors of articles and review papers that had been published in a scientific journal of a relevant field during the three previous years (2010–2012). A 3‐year period was thought to be long enough for most researchers to have published at least one scientific paper, but short enough for most of the email addresses given in those papers not to have become obsolete. The focus was on journals of paleontology, zoology, ecology, evolutionary biology, and human biology. Only journals with an ISI impact factor equal to or larger than 1.0 were considered. The exact criteria used to select the journals, as well as a full list of journal names, can be found in Appendix S1 .

Almost 58,000 unique email addresses were found in the information available online for the papers published in the selected journals during the selected time period. The full address list exceeded the capacity of the online survey system (Webropol), so the addresses were sorted in alphabetical order, and an invitation to participate in the survey was sent to the first 29,000 addresses. The remaining addresses were used for a different survey, whose results will be reported elsewhere. The first page of the online survey informed participants about the purpose of the survey. The survey was performed anonymously, and all who responded did so voluntarily. After a few reminders had been sent, a total of 1,266 persons had submitted their responses to the survey.

Although the initial sample was large and can be considered representative of the scientific community in relevant fields, the proportion of invitees who answered the survey was very small (4.4%). The sample is no doubt biased toward people who have a larger than average interest in human evolution. Therefore, the obtained answers do not reflect the opinions of the entire scientific community. Nevertheless, they can indicate whether any of the hypotheses proposed to explain the evolutionary origin of a specific human trait is universally accepted or rejected. Even if this were not the case, the survey gives indication of which hypotheses are most or least popular, although conclusions in this respect remain tentative.

The survey first asked background information of the respondent, such as gender, age, the highest academic degree obtained, number of scientific publications authored (both overall and on human evolution), degree of knowledge about human evolution, and whether the respondent has taught courses on human evolution. The second part listed fifteen human traits (such as bipedalism) and asked the respondents to rate the credibility of 51 alternative hypotheses that have been proposed to explain their evolutionary origin (such as freeing the hands for tool use or seeing over tall grass). The credibility scoring was done using a five‐point scale: very unlikely, moderately unlikely, no opinion, moderately likely, and very likely. The number of alternative hypotheses considered was ten for both bipedalism and brain size, eight for hairlessness, seven for speech, four for subcutaneous fat, and three for descended larynx. In addition, there were nine traits for which only one explanation has been proposed in the literature, and this was related to the aquatic ape hypothesis. The third part asked about the respondents’ views on criticism against AAH. All questions and a summary of the answers are presented in Appendix S2 .

2.2. Data analyses

The respondents were asked for their professional field of expertise by offering 15 alternatives. For statistical analyses, these were simplified to four categories to ensure sufficient sample size in each. The group “(paleo)anthropologist” was formed by lumping the originally separate fields “paleoanthropology” and “anthropology or archaeology.” The group “biologist” was formed by lumping all the original subfields of biology (animal physiology, anatomy, or morphology; ecology; evolution; genetics or molecular biology; other) and the group “human biologist” by lumping all subfields of human biology (cardiovascular or respiratory system, musculoskeletal system, nervous system, nutrition, other aspects of human biology). The fourth group was “other,” which contained the remaining fields (geology, paleontology, other).

Overall relationships among the hypotheses were visualized by principal coordinates analysis (PCoA), where the objects were the hypotheses and the descriptors were individual respondents, with the variable of interest being the credibility score each respondent had given to each hypothesis. A Euclidean distance matrix was calculated, such that the distance between two hypotheses reflects how differently the respondents scored their credibilities. Every respondent who gave one of the hypotheses a higher score than the other increased the final distance between the hypotheses, with the overall distance between the hypotheses equaling zero if every respondent had scored both hypotheses similarly (irrespective of whether the score itself was high or low). PCoA visualizes these pairwise distances, so the closer together two hypotheses get plotted in the ordination diagram, the more similar their explanatory value is in the opinion of an average individual respondent.

The respondents themselves were plotted in the PCoA ordination space on the basis of the scores they had given to the hypotheses. Therefore, the relative positions of the respondents reflect their opinions on the hypotheses: Respondents get plotted toward the same part of the ordination space as the hypotheses they gave highest credibility scores, and far away from the hypotheses they gave lowest scores.

Relationships between the respondents’ opinions and their backgrounds were first assessed visually with the help of the ordination diagram. We then used analysis of variance to test whether there were differences in the average opinions of respondents of different backgrounds. If so, a post hoc Tukey's honest significance test was carried out to assess which aspects of the respondents’ background were associated with differences in opinion. A more detailed breakdown of the respondents’ opinions was obtained by visually comparing the distributions of the credibility scores given to the different hypotheses. This was done both to obtain an idea of which hypotheses are most popular overall, and to see if there were differences among respondents representing different scientific fields and/or having different levels of scientific experience.

R statistical software version 3.3.2 ( https://cran.r-project.org/ ) was used both to run the analyses and to produce the graphs. The vegan package (Oksanen et al., 2015 ) was used for principal coordinates analysis. The survey data and all R code used to manipulate and analyze the data are available at Opasnet web‐workspace http://en.opasnet.org/w/Evolutionary_origin_of_human_traits . The survey data are also available from the Dryad Digital Repository https://doi.org/10.5061/dryad.s9r98 .

Principal coordinates analysis revealed some clear patterns among the hypotheses proposed to explain the evolutionary origin of specific human traits. The most eye‐catching feature of the ordination diagram in Figure  2 a is that the hypotheses got divided into two elongated groups that parallel each other but are clearly separated (the abbreviations of Fig. ​ Fig.2 2 are explained in Table  1 ). The smaller group contains all the hypotheses that evoke adaptation to swimming or diving as an explanatory factor for the emergence of a trait, and the larger group contains all other hypotheses, whether they refer to adaptation to a specific environment or to needs that emerge from a specific behavior. Because all the hypotheses in the smaller group refer to locomotion in water and have been included in the aquatic ape hypothesis (AAH), this group will be referred to as the water‐related or AAH group. For lack of a better unifying term, the larger group will be referred to as the dryland group.

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Principal coordinates analysis ( PC oA) of different hypotheses proposed to explain the evolutionary origin of specific human traits. Distances between hypotheses are based on scores given by (a) all respondents, or only respondents whose main field of expertise is (b) anthropology or paleoanthropology, (c) biology, (d) human biology, or (e) other. Each colored point corresponds to one hypothesis, and the color indicates which of the traits listed in the inset the hypothesis aims to explain. Points are scaled to reflect the average credibility score given to the corresponding hypothesis by the respondents of the mentioned expertise group. The hypothesis name abbreviations are explained in Table  1 . Each gray point in (a) corresponds to one respondent, whose position within the ordination space reflects the scores given to the hypotheses. For example, respondents plotted toward the bottom left part of the respondent cloud found the hypotheses plotted toward the bottom left of the hypothesis cloud more credible than the hypotheses at the top, and vice versa. More details on the respondent ordination are shown in Figure  3

The hypotheses on the evolutionary origin of human traits that were included in an online survey to find out how popular they are among scientists. The abbreviations are used in the figures, and the full text is copied verbatim from the survey. If ambiguous, the abbreviated hypothesis is followed by a letter depicting the trait: B = bipedalism, E = encephalization (big brain), F = subcutaneous fat, N = nakedness, L = descended larynx, S = speech, O = other

Within each of the two groups, the hypotheses got sorted by their popularity, with the average credibility score increasing toward the bottom left in Figure  2 a. A tight cluster at the extreme left of the dryland group was formed by five hypotheses with high average credibility scores (4.08–4.26 on a 1–5 scale, with 1 corresponding to “very unlikely” and 5 to “very likely”). This cluster included the most popular hypothesis for the subcutaneous fat layer (energy reserve especially for the developing brain), the descended larynx (required by articulate speech), bipedalism (use of tools and weapons), speech (social pressure for elaborate communication), and the big brain (complex social organization).

This combination might be the most popular overall scenario for the origin of these traits, but the next most popular 2–3 explanations for bipedalism (freeing hands for foraging, better view over tall grass), large brain (required by either language or collaborative hunting), and speech (required by either collaborative hunting or transmitting cultural tradition; triggered by the descended larynx) also received high average credibility scores (3.53–3.96). Their proximity in ordination space indicated that they were found credible by the same respondents, which makes it difficult to identify a single most popular overall scenario. The hypotheses explaining hairlessness were not found convincing by the respondents, as even the two most popular ones (avoidance of overheating when hunting, avoidance of ectoparasites) had average credibility scores of only 3.48 and 3.17, respectively.

Eleven of the twelve most popular hypotheses were based on inherent drivers of evolution, that is, proposing that morphological traits emerged in response to selection pressure either from a novel behavior or from a pre‐existing morphological trait. Hypotheses based on selection pressure from a new kind of external environment were less popular even within the dryland group, and the credibility scores of all the hypotheses in the water‐related group were low to intermediate (2.26–2.99). The hypotheses proposing that encephalization was triggered by improved nutrition also received intermediate popularity scores, whether achieved by cooking or by increased consumption of fish or meat (all three with credibility scores in the range 2.61–2.77). The four least popular hypotheses of all (credibility scores 1.95–2.20) were based on inherent drivers operating on dry land.

The ordination results suggest that the respondents viewed the water‐related hypotheses as an ensemble whose overall credibility they assessed independently of how they scored the credibilities of the other hypotheses. This impression is strengthened when viewing the ordination of the respondents (the gray cloud in Figure  2 a) in more detail (Figure  3 ). The main gradient among the respondents follows the average credibility score they gave for the water‐related hypotheses (Figure  2 a), and this is almost perpendicular to the (less clear) gradient of average credibility scores given for the twelve most popular hypotheses (Figure  3 b).

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The positions of the survey respondents in the space of the principal coordinates analysis shown in Figure  2 a. The ordination is the same in each panel, but colors illustrate different kinds of information related to each respondent. The colored crosses indicate the mean position of the respondents belonging to the respective subgroup. (a) Average credibility score given to the hypotheses in the water‐related group (the smaller cloud of points in Figure  2 a). (b) Average score given to the 12 most popular hypotheses in Figure  2 a. (c) Number of scientific publications authored or co‐authored (crosses of all three categories overlap). (d) Field of expertise. (e) Familiarity with hypotheses on human evolution. (f) Experience in teaching human evolution

The respondents’ position in the ordination did not seem to be related with how much scientific experience they had in general, as measured with the total number of scientific publications they had authored (Figure  3 c), but it was related with how much they knew about human evolution. Those having more background information on this specific topic (by self‐assessment, by main field of expertise being paleoanthropology or anthropology, or by having taught university courses on the topic) appeared to be more often plotted in the upper part of the ordination than respondents representing other backgrounds (Figure  3 d–f).

The visual impressions were confirmed by statistical analyses. These were carried out separately for five different subgroupings of the hypotheses. Three of these were chosen because they formed clear groups in the ordination of Figure  2 a (the dryland hypotheses, the water‐related hypotheses, the 12 most popular dryland hypotheses). The dryland hypotheses were also split into those based on environmental adaptation and those evoking behavioral drivers.

The largest effect by far on the responses was that of the field or expertise, with (paleo)anthropologists being more critical overall than representatives of any other expertise group (Table  2 ). The difference was especially large for the water‐related hypotheses: The average credibility score given by (paleo)anthropologists to this group of hypotheses (2.10 on the 1–5 scale) was much lower than the average score given by human biologists (3.02), with biologists (2.70), and others (2.67) being intermediate. For the dryland hypotheses, the difference between (paleo)anthropologists (2.97) and human biologists (3.22) was only 0.25 (vs. 0.92 in the case of the water‐related hypotheses), and the differences in the scores given by biologists, human biologists, and others were not statistically significant.

Results of Tukey's HSD test between different subgroups of respondents (line starting with Test result ~) and their average credibility scores (standard deviation in parentheses) for different groups of hypotheses: the most popular 12 hypotheses; the dryland hypotheses (the larger hypothesis group in Figure 2a); the water‐related hypotheses (the smaller hypothesis group in Figure 2a); dryland hypotheses based on behavioural demands; dryland hypotheses based on adaptation to the external environment

The results obtained with respondent subgroups based on total number of authored peer reviewed publications and total number of authored popular science publications are not shown, because they were not associated with significantly different ( p  < .05) means in any comparisons.

*** p  < .001; ** p  < .01; * p  < .05.

Overall scientific experience (as measured with the number of scientific publications authored) had no effect on the scores given to either the dryland or the water‐related hypotheses (Table  2 ). However, the more knowledge the respondents had on human evolution specifically (self‐assessed familiarity with the hypotheses, number of scientific publications on human evolution or experience in teaching human evolution), the lower the scores they gave to the water‐related hypotheses. Among biologists, those who knew more about human evolution were more critical than the less knowledgeable ones, and (paleo)anthropologists were more critical than human biologists with the same self‐assessed knowledge level.

When the dryland hypotheses were split into two groups depending on whether they were based on behavioral arguments or environmental adaptation, both groups obtained rather similar results. The main difference was that the behavioral hypotheses received somewhat higher average credibility scores, which reflects the fact that 10 of the 12 most popular hypotheses were based on behavior (on the other hand, so were the four least popular hypotheses).

To visualize the differences in opinion among the (paleo)anthropologists and representatives of other fields, we repeated the ordination of the hypotheses for each of the four respondent groups separately. In accordance with the fact that most respondents were biologists, the ordination based on the biologists’ data only (Figure  2 c) was very similar to the ordination based on all respondents (Figure  2 a). The ordination based on (paleo)anthropologists’ views (Figure  2 b) differed especially in relation to the hypotheses for bipedalism: Hypotheses that explained bipedalism by foraging, tool use, or carrying were very far removed from the main cloud and toward the opposite side than the water‐related hypotheses. In addition, the average credibility scores given to the water‐related hypotheses were among the lowest of any hypotheses. This contrasted with the situation in the ordination based on human biologists’ data (Figure  2 d), in which the water‐based hypotheses had intermediate credibility scores.

The hypotheses differed clearly from each other in the frequencies of different credibility scores, but there were some similarities in the overall pattern among those six traits for which three or more hypotheses were evaluated (Figure  4 ). None of the hypotheses received the “very likely” score from more than 46% of the respondents, but most traits had at least one hypothesis that was considered “very likely” by more than 23% and likely (either “very likely” or “moderately likely”) by 72%–90%. Many of the intermediately popular hypotheses divided the respondents rather evenly between those who found them likely and those who found them unlikely (the latter referring to the scores “very unlikely” and “moderately unlikely” combined).

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Credibility scores given by survey respondents to hypotheses that aim to explain the evolutionary origin of specific human traits. The hypotheses are sorted in order of decreasing popularity as estimated by the percentage of respondents who scored them likely (i.e., either “very likely” or “moderately likely”). Descriptions of the hypotheses as they were given in the survey are shown in Table  1

A causal relationship between articulate speech and descended larynx was accepted by most respondents, but there was no consensus on the direction of the causality. That the larynx descended because this was required by articulate speech was found likely by 84% and very likely by 43%. At the same time, that the evolution of speech was triggered by the descended larynx was found likely by 61% and very likely by 18%. In fact, 36% of the respondents scored both directions as equally likely.

Traits in the category “other” had only one explanatory hypothesis each in the survey, and this was water‐related. All of these hypotheses received many more “very unlikely” than “very likely” scores. However, four hypotheses (that baby swimming, profuse sweating, diving ability, and magnitude of diving reflex evolved as adaptations to a semi‐aquatic way of life) received so many “moderately likely” scores that the percentage of respondents who found them likely was slightly larger than the percentage who found them unlikely (Figure  4 ).

Details on how the hypotheses were scored by respondents representing different fields of expertise are shown in Figure  5 . In accordance with the statistical test results, most hypotheses received rather similar scores from respondents of all fields of expertise. However, (paleo)anthropologists were clearly more critical than representatives of the other fields in relation to several hypotheses, including: that nakedness evolved to avoid ectoparasites, that the big brain evolved because warfare caused pressure for higher intelligence, and that any traits evolved as adaptations to swimming or diving.

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Frequencies of credibility scores given to hypotheses aiming to explain different traits (columns) by respondents of different fields of expertise (rows). In each panel, the answers are, from left to right, “very likely,” moderately likely,” “no opinion,” “moderately unlikely,” and “very unlikely.” Hypotheses that have been included in the aquatic ape hypothesis are shown in shades of blue and green. Those dryland hypotheses for which the opinions of anthropologists and other expertise groups clearly diverged are shown in magenta. The other hypotheses are in shades of brown, with darker colors given to hypotheses that received higher average credibility scores in the survey

There was a lot of variation among the traits in how many of the proposed explanations the respondents found convincing (Figure  6 ). For any one trait, 33%–64% of the respondents did not find any of the proposed hypotheses “very likely,” while 19%–38% found exactly one and 8%–45% more than one. Ten respondents (0.8%) explained that they did not score any of the hypotheses as likely, because they do not believe that humans have evolved at all (most of them explicitly referred to special creation by God).

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The number of hypotheses (colors) proposed to explain each human trait (rows) that each respondent found very likely (left panel) or likely (either very likely or moderately likely; right panel). The total number of hypotheses included in the survey is shown after the name of each trait

The survey asked respondents’ opinions on twenty critical arguments that have been presented against the aquatic ape hypothesis. For most arguments, the modal response was “no opinion,” especially among those 43% of the respondents who had never heard of AAH before. Nevertheless, some arguments were clearly more frequently agreed with than others (Figure  7 and Table  3 ). The most widely accepted critique was that not all aquatic mammals have naked skin, so hairlessness cannot be considered an aquatic adaptation. In the other extreme, less than 3% of the respondents fully agreed and less than 12% mostly agreed with the critique that AAH is unscientific or not worthy of attention for the reasons given; in most cases, the number of respondents who strongly disagreed with these critiques was larger than the number who mostly or fully agreed.

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The degree to which respondents representing different expertise fields agree with critique presented against the aquatic ape hypothesis. The full description of each point of critique can be found in Table  3

Points of critique presented against the aquatic ape hypothesis (AAH). The abbreviations are used in Figure  7 , and the full text is copied verbatim from the survey

4. DISCUSSION

The main results of our survey can be summarized as follows: (1) There was no general agreement among the respondents on why any of the uniquely human traits have evolved: None of the proposed hypotheses was universally either accepted or rejected. (2) For any individual trait, the percentage of respondents who found none of the hypotheses “very likely” was between >30% (bipedalism) and >65% (nakedness). (3) In general, opinions on the credibility of the hypotheses were independent of a person's background (gender, age, field of expertise, degree of scientific experience), but (paleo)anthropologists were clearly more critical than representatives of other fields. (4) The hypotheses that mention adaptation to swimming or diving as an explanatory factor were found much less credible by (paleo)anthropologists and slightly more credible by human biologists than by biologists and representatives of other fields. (5) Most respondents were critical about the aquatic ape hypothesis (AAH), but only a small minority considered it to be unscientific.

Of course, all conclusions based on the survey data must be considered tentative only, because the response rate was very low, and it is possible that the results are biased. Members of some subgroup might have been more likely to respond than members of some other subgroup, and the average credibility scores given to the different hypotheses by the respondents may not be representative of the opinions of all scientists in the background population. However, it is unlikely that a lack of general agreement on the drivers of trait evolution or such a clear difference in opinion between (paleo)anthropologists and others could have emerged just as a result of biased sampling.

Our results did not reveal a set of explanations that would collectively provide a coherent and popular scenario for the origin of all (or even many) human traits. Indeed, some of the hypotheses that had almost equal and rather high average credibility scores explained the same trait, whereas for other traits, no hypothesis emerged as particularly popular. Against this background, it is interesting that almost half of the respondents fully or mostly agreed with the statement that the aquatic ape hypothesis “is not needed, because all human traits can be explained by terrestrial scenarios”.

The lack of agreement on why humans evolved the traits we have today is very obvious in our results: No hypothesis was universally accepted, and for most traits, there were several almost equally popular alternative hypotheses rather than one that would generally be considered superior to the others. None of the hypotheses received the score “very likely” from more than half of the respondents or obtained an average credibility score higher than 4.26 (of 5). For hairlessness, the most popular hypothesis was thought to be “very likely” by only 16% of the respondents, and its average credibility score (3.48) was closer to 3 (which is the limit between being considered more likely than unlikely) than to 4 (moderately likely). In addition, for only two of the traits (subcutaneous fat layer and descended larynx), the most popular hypothesis was found at least moderately likely by almost all respondents at the same time as the next most popular hypothesis was found clearly less likely. This may partly reflect the fact that fewer alternative hypotheses have been proposed for these traits than for many of the others included in the survey.

Importantly, lack of agreement did not reflect just ignorance on the topic among nonspecialists, because the responses were, in general, very similar between anthropologists and respondents representing other fields of science. In fact, anthropologists were even more skeptical about all hypotheses than representatives of the other fields were. In other words, outsiders were slightly more convinced that the proposed hypotheses are plausible than those who work in the field. Maybe anthropologists (especially paleoanthropologists) are more systematically trained to be wary of just‐so‐stories (explanations of past events and processes backed up by little or no evidence) than students in nearby fields are. It is also possible that outsiders are somewhat less likely to question hypotheses proposed within an unfamiliar field. This could be because they do not feel qualified to do so, or because they have not heard of the debates that draw attention to the weaknesses of the hypotheses.

Our results conform with the widespread belief that professionals in the field of human evolution are more critical toward the aquatic ape hypothesis (AAH) than outsiders are (Langdon, 1997 ; Bender et al., 2012 ; see also nonscientific sources such as Hawks, 2005 ; Moore, 2012 and Wikipedia: Aquatic Ape Hypothesis: Talk). However, this did not seem to be due to overall scientific ignorance, because how respondents assessed the credibility of the hypotheses proposing adaptation to swimming or diving was independent of both their overall scientific experience level and how they assessed the credibility of the other hypotheses. Interestingly, those whose main field of expertise is human biology had the most positive attitudes toward the water‐related hypotheses, giving them an average credibility score that was as much as 0.9 units higher (on a 1–5 scale) than the average score given by (paleo)anthropologists.

The difference in average opinion between (paleo)anthropologists and other scientists can be interpreted in two opposite ways. On the one hand, those who know the field of human evolution best may be best positioned to make a justified evaluation of the validity of the alternative hypotheses. On the other hand, prior knowledge may induce one to reject unconventional hypotheses offhand merely because they challenge the established paradigms of a field (Bender et al., 2012 ; Klayman, 1995 ). Obviously, the two interpretations lead to opposite conclusions on whether or not the critical attitude of the (paleo)anthropologists can be taken as evidence that AAH is flawed. In our survey, a vast majority of the respondents who had an opinion on the issue disagreed with the statement that AAH can be ignored because its main proponents are not professionals in the field of human evolution. This was the case both overall and within each field of expertise separately, although the proportion of respondents who agreed with the statement was higher among (paleo)anthropologists than among representatives of the other fields.

In this context, it is also interesting that the respondents’ assessment of the credibility of the water‐related hypotheses did not depend on the number of scientific papers they had authored. This indicates that established scientists are no more likely to reject or accept these hypotheses than junior scientists are—unless their scientific experience relates directly to the field of human evolution. A vast majority of the respondents disagreed with the critique that AAH is unscientific. Of course, this does not mean that they would consider the explanations proposed by AAH to be correct, and indeed, all the hypotheses related to AAH received relatively low credibility scores (although not as low as the least popular dryland hypotheses).

If, for the sake of argument, we accept the most popular explanation for each trait to be the correct one, a scenario of evolution by internal drive emerges: The large brain evolved because complex social organization required higher intelligence, the subcutaneous fat layer evolved to serve as an energy reserve for the developing brain, articulate speech evolved because there was social pressure for elaborate communication, the larynx descended because this was required by articulate speech, bipedalism evolved to make the use of tools and weapons easier, and nakedness evolved to avoid overheating when hunting. For most traits, the next most popular explanation was not far behind in popularity. Most of these were also based on inherent drivers, but sometimes in the opposite temporal sequence (e.g., articulate speech was triggered by the descended larynx; large brain evolved because it was required by articulate speech). We found this result disturbing, because the overwhelming popularity of hypotheses based on inherent drivers gives the impression that human evolution is generally thought to have been goal‐directed. This would be in conflict with the current understanding (explained in every evolutionary biology textbook) that evolution has no foresight.

Overall, the survey revealed no general agreement among the respondents: None of the proposed hypotheses on why specific uniquely human traits have evolved was universally either accepted or rejected. Nevertheless, identifying and quantifying what is not generally known and agreed upon can be useful in itself, as it may help to focus future research on answering the most important open questions. Clearly, there is still a long way to go before the question “why are humans so different from other primates” has been answered in a comprehensive and generally satisfactory way.

DATA ACCESSIBILITY

Conflict of interest.

None declared.

AUTHOR CONTRIBUTIONS

HT designed and conducted the survey and led the writing. All authors discussed the results and planned the data analyses together. The R code used to analyze the data and draw the figures was written by MT with contributions from JT.

Supporting information

Acknowledgments.

We thank Carlos Peña for writing the code to extract respondents’ email addresses from the Internet; Mirkka Jones, Kalle Ruokolainen, and Timo Vuorisalo for comments that helped to improve the survey questions; and Jouko Tuomisto for comments on the manuscript.

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History: Evolution of Humans Essay

The first picture demonstrates the areas of the settlement of modern humans’ predecessors, namely, Homo erectus , Homo neanderthalensis , and Homo sapiens , as well as the times of the migration of Homo sapiens to different regions. This map is directly related to chapter 1, which describes how and when evolution led to the emergence of modern humans and what distinctive features humans’ predecessors possessed. The chapter also pays detailed attention to the description of Homo sapiens and their way of life because modern people belong to this species.

The emergence of Homo erectus was a significant stage of human evolution. This species appeared about 1.8 million years ago and was distinguished by walking upright and having a considerable brain capacity (Pollard et al., 2019). Homo erectus could travel long distances and use fire; because of their large brain size, these human predecessors had a long period of maturation, which caused them to live in extended families (Pollard et al., 2019). As the map shows, Homo erectus originated in Africa and migrated to Southwest, South, and Southeast Asia, as well as to the territory of modern China.

The map also demonstrates that Homo sapiens emerged in eastern Africa 200,000 years ago. Like their predecessors, Homo sapiens migrated across Southwest Asia to central Asia about 120,000 to 50,000 years ago (Pollard et al., 2019). They also occupied the northeastern part of East Asia, where they adapted to the cold climate (Pollard et al., 2019). Around 30,000 years ago, Homo sapiens moved to the area linking North America and Siberia, and 16,000 years ago, they migrated to North America, where they traveled eastward and southward to South America (Pollard et al., 2019). Finally, the map shows the area inhabited by Homo neanderthalensis , which was an unsuccessful branch of human evolution (Pollard et al., 2019). This species occupied Europe and Southwest Asia but died out 40,000 years ago because of environmental changes.

The second picture portrays the world in the third millennium BCE and is related to chapter 2, which describes life in early cities, villages, and pastoral nomads. The map shows that river-basin societies emerged in the basins of large rivers. Mesopotamia appeared between the Tigris and Euphrates Rivers, and Egypt emerged on the banks of the Nile River (Pollard et al., 2019). The Indus urban culture was established along the Ravi River, and China was based on the area between the Yellow and Yangzi Rivers (Pollard et al., 2019). River-based communities were located near rivers and were not situated in the steppes or rugged areas because the water was crucial for the development of urban cultures. Water allowed people to develop agriculture and create a surplus of food, which was why cities attracted more people and enabled them to engage in occupations other than growing crops.

In less geographically advantageous places, people lived in villages or led a nomadic lifestyle. Pastoral nomadic communities were small and did not have permanent dwellings (Pollard et al., 2019). They inhabited arid environments and steppes of Africa and Eurasia, moving according to a seasonal pattern (Pollard et al., 2019). Transhumant herders lived alongside agrarian communities, and these types of communities were involved in a mutually beneficial interaction. Since transhumant herders changed places and were engaged in hunt and livestock breeding, they supplied agrarian communities with meat and animal products. In exchange, agrarian communities gave them tools, pottery, and grains. In the places where pastoral nomadic communities were prevalent, cities could not emerge because the environment did not allow for large-scale farming, which was necessary for creating product surplus. The map also shows areas of widespread village culture in Europe and the Tehuacán Valley. In these regions, agriculturally productive areas were small, and people were often involved in wars for resources.

Pollard, E., Rosenberg, C., Tignor, R., Adelman, J., Aron, S., Brown, P., Elman, B., Kotkin, S., Liu, X., Marchand, S., Pittman, H., Prakash, G., Shaw, B., & Tsin, M. (2019). Worlds together, worlds apart with sources (2 nd ed., vol. 1). W. W. Norton & Company.

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Evolution of Human

Updated 30 June 2021

Subject Biology

Downloads 34

Category Science

Topic Evolution ,  Human

The human evolution has gone through several steps. In this essay, the focal point is on the gradual change of the heritable and biological traits of human organisms with emphasis on the difficulties they undergo within the environment. The evolutionary methods give rise to biodiversity at all tiers of human species. The focus is also on human viruses and how the physique immune system reacts to the pathogens. In human evolution, the new groups emerge in response to the desires of the difficult physical, economic and social surroundings. At this juncture, the need for food is cosy by literally gathering the uncommon or limited food commodities. At some point, looking becomes a source of obtaining food items for the people. The human society, therefore, is determined by the levels of political and sexual/biological relations they engage in. The modern human evolution is also ratified by the rapid development of language and culture which is said to have transformed humankind to its states presently. The scientific study of human development is known as paleoanthropology, and it involves analysis of human biological make up, cultural traits, and society. Through the field, it is possible for scientists make appropriate comparison between humans and other species. Here, the emphasis is made on the genes, behavior, body forms and the physiological make up. The scientists can also understand how limitations and potentials of people have changed over time due to evolution. Paleoanthropology also focuses on investigating the scientific origin of the defining traits of people, over millions of years ago. Early human fossils, offers the most reliable clues about the human ancient past. Evidences such as bones, pottery, skulls, tools, footprints, butchery marks on animal bones, tools, weapons, clothing, ornaments, settlements among others. Some of the remains were buried and preserved naturally but were later exposed to the ground surface by rain, floods, rivers, wind, digging or soil erosion. Through the study of the bone fossils, scientists can understand human physical appearance and how such traits have transformed over time. The fossilized bones are of various sizes, shapes, and markings that are believed to be left by muscles. Through close examination of the bones, the scientists can detect how the brains size of early humans have changed over time. Also, by studying the archeological shreds of evidence, the scientists can understand how early human beings made and utilized their tools. It is also possible to recognize the kind settlements that people lived in in the past. How their lifestyles have changed over time is a clear indication of the gradual human evolution, and this depends fully on the type of archeological evidence at stake.All human beings and other species originated through biological evolution (Relethford, 2008). The process of evolution analyzes the various changes that species undergoes through before their extinct or death. For instance, human beings can reproduce sexually resulting in fertile offspring. Upon maturation, the offspring too can breed and give birth to other productive humans. In this system, the scientists classify the modern human system as Homo sapiens. The surviving of the offspring depends on a lot of factors, parental care being the primary factor. Other factors include things such as environmental conditions (weather and climate), diseases, nutritional values administered to the young ones, culture, and beliefs of the people.The evolution process also occurs as a result of the changes in the genetic make-up of the organisms which determines the particular characteristics of the species. Genes constitute the DNA information that is significant to the overall growth and development of an individual. DNA is a chemical molecule that is inherited specifically from the parents. The molecular expressions of the DNA gene embedded in the population connected to hereditary and kinship. It is present in all nucleus cells of human beings, and it determines their appearance and how they respond to specific occurrences in the environment. The information in the DNA can be altered through the process of mutation (Plyusnin et al, 1996). Genes influences the behavior and of the body over time. Therefore, the characteristics one inherits genetically would ascertain the chances of the organism to survive or reproduce. Evolution alters the genetically acquired ways of growing and developing that characterizes a given populace (individuals of the same species occupying a given habitat). Offspring inherit the adaptive genetic components from their parents. The changes are than replicated in the entire population. Such changes enhance the ability of the offspring to survive and for conception. Changes in the environment may change the genetic make-up of the human species, and this can alter overall ways of life of the species, for instance, what they consume as food, where they live and how they grow. Human evolution takes place since the new variations in the early ancestors facilitates new capabilities to adapt to fluctuations in the environmental conditions, and so transformed the way of life of the humans (Balter, 2005). Other factors that show humans are evolving includes, human brains are still shrinking, the persistent resistance to diseases which is as a result of body cell mutations, human fertility rates which determine their ability to give birth to more offspring (Stock, 2008). Upon reaching the environment, their chances of survival are determined by natural selection. In this case, once survival depends on their ability to resist diseases and how they respond to treatments.The Role of Viruses in Human Evolution.Viruses are said to be the major drivers of human evolution, that is, the constant battles between the viruses and the host (humans) all along is what biologists believe that is a major driving force of evolution (Van Blerkom, 2003). Animal viruses are classified into various families depending on the viral genome i.e. DNA or RNA. The adaptive patterns caused by the viruses are too much strong and clear. The adaptations mainly occur in proteins which primarily interacts with the viruses. Proteins consist of essential nutrients necessary for the body of mammals. The nutrients are crucial to a vast array of functions that is responsible for the cells’ functioning. Recent studies reveal that certain variations in the size, shape, composition of proteins are what have assisted human beings and other mammals to respond to viruses. The revelation is what has helped scientists to come up with the new therapeutic leads to conquer or take control of the threats that results from virus attack. Like any other pathogens, the virus is a disease-causing germ. The body should have defensive mechanisms to respond to any threat that occurs as a result of the virus invasion. The viruses alter the functions of the body cells and organs. Presumably, certain parts of the cells have been used in the fight against viruses, and this is done without causing detrimental threats to the organs' functionality.When the virus hijacks the body, proteins react to enhance the needed immunity against the threat that may be due to the disease (Feschotte & Gilbert, 2012). The immune system, therefore, assists the body to adapt. Therefore, viruses have affected the humans in almost all aspects of their lives. The availability of proteins in the body makes essential cellular functions possible. Hence the scientists can use the analogy to be able to enact ways or cures to face future threats by the virus. Whenever a pandemic or epidemic strike, the humans must be able to develop the means to adapt to such conditions. Failure to which implies that their chances of survival diminish. Hence, they risk becoming extinct. It is, therefore, the duty of the health practitioners and scientists to apply the visible changes in protein to establish new ways that would help the body adapt. Through this knowledge, the scientists are in a position to explain why similar species evolve completely different methods in performing the same cellular functions like DNA duplication or creation of cell membrane (Deininger et al, 2003). Therefore, viruses are believed to be withholding vital information concerning how humans have evolved over time.When the virus invades the body, it hijacks nearly all the functions of the host human cells. After that, the virus can replicate and spread to the majority of the parts of the body cells and organs (Plyusnin et al, 1996). This suggests that viruses are responsible drivers of the human cellular evolution. Because it stays within the body, the virus is believed to have more impact on the human evolution than other evolutionary pressures such as environmental conditions, socialization or tradition, and cultural beliefs. Virus invasion into the body has been a cause of some biological mysteries such as the following: closely related species evolving different machinery to perform same cellular functions, production of membranes or replications of the DNA (Van Blerkom, 2003). Human beings have involved in constant wars with the virus, for instance, the Human Immune Deficiency Virus which severely harms the body. The HIV is what causes AIDS, and once it enters the body, it multiplies rapidly and can result in the death of the victims. AIDS is one of the leader killers of people living on earth. Some believe it is a curse, but it is a product of viral infection of the body. Considering such effects, the humans have engaged in constant battles with the virus to control its spread or acquisition amongst different individuals. The insight is to help in the fighting of diseases today.Unlike most of the viruses that infect, replicate, spread and later disappear away from the host, the retroviruses nudge their way into the genome of the host where they are copied and passed to daughter cells for the life of the hosts (Feschotte & Gilbert, 2012). The retrovirus cell is said to have sneaked its way into one of the sperm or egg cells of the human ancestors. The virus is, therefore, able to be passed on through subsequent generations. Hence, the finding that the host and virus have become one and the same thing. This goes by the saying that without the retroviruses, humans might have never evolved their placentas, and this means humans would be extinct by now. The viral DNA uses its genes to replicate itself into the host’s genome. The copies spread in different parts of the body at a different point in time. Such symbiotic relationship between the virus and the host is what constitute raw materials for developing new body functions (Stock, 2008).Therefore, if humans or other mammals lived millions of years ago, the symbiotic relationships between them and the retroviruses is what enabled them to evolve a placenta over the years and the upcoming generations. For the fetus to get mature in the mother’s womb/uterus, the human enacts certain ways to get oxygen and specific nutrients (Deininger et al, 2003). The animal also would remove wastes and keep blood supplies separate. The early animals had a way of sparing the viral parts left in the junk drawers of the genome and utilize the viral gene to produce a placenta. The process, together with other symbiotic viruses is what transform the ball cells into a fully formed squalling newborn. It also protects the infants from pathogens. Junk DNA is a portion of the symbiotic viruses that is a significant catalyst in the evolution of new species. Therefore, the evolution of pregnancy through the placenta is considered a clear evidence that the viruses occupying the human genome are responsible for the rise in new species. Hence, the role of the endogenous retroviruses in human evolution implies that the DNA diminishes the boundary between humans and virus. In other words, human and virus are part of each other. Thousands of viruses are embedded in the human genomes, and each of them has got potential effects (Van Blerkom, 2003). According to Cedric Feschottea, Geneticist at the University of Utah, viruses take a crucial role enhancing evolution of the mammalian immune system. According to him, the viruses are equipped with specified weapons that are destined to evade the human immune system. For instance, Mer41, a virus that infiltrated the genome forty- five to sixty million years ago, controls one of the proteins in humans, and this also has an effect on the human immune system. Due to the human vulnerability to infectious diseases, there is need to improve ones’ ability to survive the pathogens. Such protection can be derived from viruses, and this has an influence in the evolutionary process of human beings. Therefore, endogenous viruses have had impacts on human evolution and still affects our ways of life. The retroviruses also have an influence on how people think as species. That there exists an intimate relationship between the virus and the human self, hence, through a constant exchange of useful DNA, humans have molded the perceptions about themselves as components of the DNA which are infiltrated by the viruses.However, like any other pathogens, the effects of viruses on human are not always beneficial as they also result to infiltration of deadly diseases and infections into the body. For example, diseases like common cold, HIV/aids, chickenpox, herpes, human papillomavirus (HPV), Mumps, Measles, and Rubella, viral meningitis, viral pneumonia, viral gastroenteritis, Ebola and viral hepatitis (Plyusnin et al, 1996). The viral diseases are contagious hence can easily be spread from one person to the other, for instance, through engaging in sexual intercourse with a person infected with a virus transmitted sexually. Other ways include: eating contaminated food or drinks contaminated with a virus, breathing in air droplets from a person infected by a virus, indirect transmission e.g. through insects such as mosquitoes, tick, or mouse. Upon entering the body, the virus multiplies and occupy the entire body system. The viral diseases portray a variety of symptoms which vary depending on factors such as; type of viral infection, age, and overall ones’ health. The antibiotics only treat diseases caused by bacteria, hence cannot be applied in the treatment of a viral infection. The common cold is the most common viral disease, and it is caused by the virus attacking the upper respiratory tract which is made up of the nose and the throat (Krug et al (2003). It is generally self-limiting on the healthy individuals. Therefore, it implies that the viral infection only increases illness for a particular period. After which, the body immune system responds by attacking the virus, the symptoms disappear and then the person recovers. In some cases, viral infections develop serious and life-threatening complications, for instance, pneumonia, dehydration or secondary bacterial infections. People who are most vulnerable to such complications possess certain symptoms like; weak or suppressed immune system and are usually the very young or old individuals. Some of them have chronic infections (Feschotte & Gilbert, 2012). Furthermore, some of the viral infections transmitted sexually are more dangerous and lead to death and sufferings. The reason is that they have no permanent cure. Such diseases include HIV/AIDS, EBOLA, and HPV. It is, therefore, advisable that one seeks immediate medical attention if he or she suspects having a viral disease or is exposed to any sexually transmitted infection.According to Krug et al (2003), viruses are responsible for the taking of countless lives, for instance, the Hantavirus comprises multiple viruses that can result in lung diseases, fever or kidney infection. Others are like the Lass and bird flu which is usually transmitted by rodents, Marburg virus which constitutes 90% of mortality rate, Machupo virus which causes constant bleeding and high fever, Junin virus responsible for tissue inflammation, Kyasunur forest virus causing muscle pain, high fever and bleeding. Apart from the above examples is Dengue fever which is spread by mosquito and boast extremely high rates of fatality. It affects between fifty to hundred million people annually. It is also a famous disease in most tourist’s destinations such as Thailand, Philippines, and India. Consequently, there exists the Ebola virus which is also very deadly and has resulted in thousands of deaths in the West Africa and beyond.To treat the viral infections, it is vital that the scientists try their best in addressing the specific complications and symptoms of the diseases (Münz et al, 2009). For instance, the spread of Ebola virus is controlled by maintaining oxygen levels, treating every infection that arises, providing fluids as well as keeping stable the electrolyte levels. Above all, maintaining the blood pressure level would be a meaningful remedy. For other viruses, the scientists are currently engaged in continuous research to develop appropriate vaccines that would help in keeping them at bay. Enhancing the protein adaptations while responding to the particular symptoms would also be a necessary move for the scientists. Nevertheless, in this highly mobile world, the development of the international trade, as well as the presence of millions of people traveling through the air at any moment, has given the viruses more opportunities to spread and disseminate globally. The growth in human mobility across the world has connected pathogens e.g. bacteria, fungi, and viruses to new and growing hosts of the population thus contribute to the emergence and reemergence of disease epidemics.ReferencesBalter, M. (2005). Are humans still evolving? Science, 309(5732), 234-237.Deininger, P. L., Moran, J. V., Batzer, M. A., & Kazazian, H. H. (2003). Mobile elements and mammalian genome evolution. Current opinion in genetics & development, 13(6), 651-658.Feschotte, C., & Gilbert, C. (2012). Endogenous viruses: insights into viral evolution and impact on host biology. Nature Reviews Genetics, 13(4), 283-296.Krug, R. M., Yuan, W., Noah, D. L., & Latham, A. G. (2003). Intracellular warfare between human influenza viruses and human cells: the roles of the viral NS1 protein. Virology, 309(2), 181-189.Münz, C., Lünemann, J. D., Getts, M. T., & Miller, S. D. (2009). Antiviral immune responses: triggers of or triggered by autoimmunity? Nature Reviews Immunology, 9(4), 246-258.Plyusnin, A., Vapalahti, O., & Vaheri, A. (1996). Hantaviruses: genome structure, expression and evolution. Journal of General Virology, 77(11), 2677-2687.Pritchard, J. K. (2010). How we are evolving. Scientific American, 303(4), 40-47.Relethford, J. H. (2008). Genetic evidence and the modern human origins debate. Heredity, 100(6), 555-563.Stock, J. T. (2008). Are humans still evolving? EMBO reports, 9(1S), S51-S54.Van Blerkom, L. M. (2003). Role of viruses in human evolution. American journal of physical anthropology, 122(S37), 14-46.

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What Is the Difference Between Early Modern Humans and Ancient Humans?

S ome 300,000 years ago, Homo sapiens split off from a long line of human-ish primates to become the first fully human species, with abilities and ingenuity unrivaled in Earth's history. But back then, in terms of behavior and intelligence, those early humans wouldn't have seemed so different from the other hominins they shared the landscape with - Neanderthals, Denisovans, Homo erectus and so on.

Now picture one of these ancient people beside a 21st-century counterpart, and consider how wide the gap has grown. The average person today zips from place to place in a personal metal shell that would put any cheetah to shame. They seek beauty in paintings, novels and other depictions of worlds that don't even exist. They are embedded in socio-political networks vastly larger than the entire population of our prehistoric ancestors.

And yet! Genetically (more or less), we are them. We, with our spaceships and particle colliders, our operas and crème brûlées, our megacities and globe-spanning systems of cooperation, are made of the same essential stuff as those club-wielding nomads cooking mastodon steaks on a spit.

So, how did we get from there to here?

What Is an Ancient Human?

An ancient human is identified not by a single moment in evolution, as this process is too gradual to pinpoint when exactly we became "human." We all share a single genetic ancestor, certainly, but that doesn't mean there was any significant difference between them and their contemporaries; they just won the reproductive lottery.

When Did Modern Humans First Appear?

Based on fossil and DNA evidence, people that looked like us (anatomically modern) appeared in Africa about 300,000 years ago . But the archaeological record of tools and artifacts suggests they only started to act like us (behaviorally modern) 50,000 to 60,000 years ago, after thousands of generations of stasis.

This abrupt shift is sometimes called the "great leap forward" (not to be confused with Mao Zedong's disastrous economic campaign of the same name). Experts disagree on how to explain the lag between anatomic and behavioral modernity, but for whatever reason, it seems that humans only reached an intellectual apex long after they'd come to resemble us in most other ways.

Read More: What Did Ancient Humans Look Like?

Ancient Humans vs. Modern Humans Behavior

(Credit: maradon333/Shutterstock)

If we compare ourselves with pre-leap humans, then, we find vast differences. Take the development of the concept of symbolism, for example: The use of objects, images, and signs to represent ideas , is a huge part of what makes us, us. It's the key that unlocked language, along with cultural, religious, and technological innovation. That's why archaeologists are always on the lookout for evidence of " symbolically mediated behavior ," like ritual burials, bone flutes, and cave paintings.

Problem Solving and Long-Range Planning

Another staple of modern behavior is a knack for problem-solving and long-range planning. In the archaeological record this shows up as a sudden surge, beginning roughly 60,000 years ago, in the production of advanced artifacts like fish hooks , bows , and sewing needles . Around the same time, our species was rapidly colonizing the planet, including voyages to Australia and other Pacific islands that demanded maritime expertise.

What drove this unprecedented, world-girdling success? "It was not their technology alone," as cognitive archaeologists Frederick L. Coolidge and Thomas Wynn write in The Rise of Homo Sapiens. "It was something about their minds, an ability they possessed that their cousins did not."

Executive Function

That "something," in their view, is executive function : A set of complex mental processes that, among other things, enable us to achieve our goals by planning ahead, focusing our attention, reasoning abstractly and exercising self-control. The neuropsychologist Muriel Lezak has called it "the heart of all socially useful, personally enhancing, constructive, and creative abilities."

It's doubtful our species would've gotten far without executive function, a feature of the brain's evolutionarily recent frontal lobe . These capacities allowed ancient humans to refine tools, coordinate elaborate hunts, and even sail to distant, unseen lands.

Read More: How Did Humans Evolve?

The Evolution of Human Societies: From Stone Age to Modernity

(Credit: Vara I/Shutterstock)

But this isn't the full story - in case you didn't notice, there have been some major developments since behavioral modernity emerged near the end of the Stone Age. The mental landscape of our upper-paleolithic progenitors may have been similar to our own, but in many ways, they were still closer to the earliest humans than to those in the present day.

One possible explanation of what's happened since then is that, in fact, we haven't changed a whole lot as individuals . Evolutionary psychologist Nicholas R. Longrich notes that the great thinkers of antiquity, like Aristotle and Buddha, were clearly just as well-endowed with intellect as anyone alive now.

The Role of Global Networks in Human Evolution

What has changed are the increasingly larger and more global networks in which we live. "Much of the difference between our ancient, simple hunter-gatherer societies and modern societies," he writes, "just reflects the fact that there are lots more of us and more connections between us."

That's important because innovation grows in step with population: The more people, the more likely one of them will be the genius who invents a better spearhead (or wheel, or combustion engine, or supercomputer), setting off an intricate feedback loop in which culture evolves to ever greater levels of sophistication. And a handful of special innovations, like agriculture and writing, truly turbocharged human progress, launching us far beyond the horizons of prior generations.

In other words, it's not that our cognitive hardware has improved since the first behaviorally modern humans, just that we enjoy the benefits of thousands of years of accumulated knowledge.

  Read More: 7 Groundbreaking Ancient Civilizations That Influence Us Today

Genetic Mutation and Evolution Across Continents

(Credit: Lightspring/Shutterstock)

So much for our brains. When it comes to physical appearance, a glance at any diverse crowd shows that evolution was hard at work as humans fanned out across the continents.

When they embarked on their long journey out of Africa, our ancestors encountered all sorts of new environments and were forced to continuously adapt. Some of the results are visible: Genetic mutations for dark skin allowed them to withstand the harmful UV radiation of sunny locales, while small noses could better warm the cold air they inhaled in northern climates.

Other adaptations were subtler, but just as influential. Lactase persistence , for example, evolved in populations with domesticated livestock, allowing them to digest milk throughout their lives rather than only during infancy. And in mountainous Tibet, people living at high altitude acquired larger lungs to make efficient use of the region's thin air.

Read More: Human Evolution in the Modern Age

Are There Ever Evolutionary Mismatches?

(Credit: Maksim Denisenko/Shutterstock)

Amid all the changes of the past few millennia, the monumental shifts in our world and way of life, it's also surprising how much we've stayed the same. Much of our behavior is calibrated for a long-gone ancestral environment, and we're now often confronted by evolutionary mismatches - many traits that helped our forebears have negative consequences for us today.

Take our nearly insatiable cravings for tasty food. Ancient people often dealt with food scarcity, so it made sense for them to gorge whenever the opportunity arose. In the modern context of perpetual abundance, however, this instinct has fueled an epidemic of overeating and obesity.

All of this, the good and the bad, makes up our species' legacy - at once fluid and enduring, it shapes our lives, our civilizations and, increasingly, the world around us. Maybe, once we brought them up to speed on spaceships and crème brûlées and what not, those early humans would even see in our world something of themselves.

Read More: Finding Human Ancestors in New Places

Article Sources

Our writers at  Discovermagazine.com  use peer-reviewed studies and high quality sources for our articles, and our editors review for accuracy and trustworthiness. Review the sources used below for this article:

Nature . New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens.

The Nature Education. The Transition to Modern Behavior.

Research Gate. The origin of symbolically mediated behaviour.

Science Direct . Middle Stone Age bone tools from the Howiesons Poort layers, Sibudu Cave, South Africa.

Nature. Human occupation of northern Australia by 65,000 years ago.

National Library of Medicine . Executive Functions.

Science Direct . Frontal Lobe.

The Conversation. When did we become fully human? What fossils and DNA tell us about the evolution of modern intelligence.

National Library of Medicine. The Protective Role of Melanin Against UV Damage in Human Skin.

PennState. Nose form was shaped by climate.

National Library of Medicine. Evolution of lactase persistence: an example of human niche construction.

National Library of Medicine. High altitude adaptation in Tibetans.

National Library of Medicine. Evolutionary mismatch.

National Library of Medicine. Evolutionary Considerations on Social Status, Eating Behavior and Obesity.

What Is the Difference Between Early Modern Humans and Ancient Humans?

EU AI Act: first regulation on artificial intelligence

The use of artificial intelligence in the EU will be regulated by the AI Act, the world’s first comprehensive AI law. Find out how it will protect you.

A man faces a computer generated figure with programming language in the background

As part of its digital strategy , the EU wants to regulate artificial intelligence (AI) to ensure better conditions for the development and use of this innovative technology. AI can create many benefits , such as better healthcare; safer and cleaner transport; more efficient manufacturing; and cheaper and more sustainable energy.

In April 2021, the European Commission proposed the first EU regulatory framework for AI. It says that AI systems that can be used in different applications are analysed and classified according to the risk they pose to users. The different risk levels will mean more or less regulation. Once approved, these will be the world’s first rules on AI.

Learn more about what artificial intelligence is and how it is used

What Parliament wants in AI legislation

Parliament’s priority is to make sure that AI systems used in the EU are safe, transparent, traceable, non-discriminatory and environmentally friendly. AI systems should be overseen by people, rather than by automation, to prevent harmful outcomes.

Parliament also wants to establish a technology-neutral, uniform definition for AI that could be applied to future AI systems.

Learn more about Parliament’s work on AI and its vision for AI’s future

AI Act: different rules for different risk levels

The new rules establish obligations for providers and users depending on the level of risk from artificial intelligence. While many AI systems pose minimal risk, they need to be assessed.

Unacceptable risk

Unacceptable risk AI systems are systems considered a threat to people and will be banned. They include:

  • Cognitive behavioural manipulation of people or specific vulnerable groups: for example voice-activated toys that encourage dangerous behaviour in children
  • Social scoring: classifying people based on behaviour, socio-economic status or personal characteristics
  • Biometric identification and categorisation of people
  • Real-time and remote biometric identification systems, such as facial recognition

Some exceptions may be allowed for law enforcement purposes. “Real-time” remote biometric identification systems will be allowed in a limited number of serious cases, while “post” remote biometric identification systems, where identification occurs after a significant delay, will be allowed to prosecute serious crimes and only after court approval.

AI systems that negatively affect safety or fundamental rights will be considered high risk and will be divided into two categories:

1) AI systems that are used in products falling under the EU’s product safety legislation . This includes toys, aviation, cars, medical devices and lifts.

2) AI systems falling into specific areas that will have to be registered in an EU database:

  • Management and operation of critical infrastructure
  • Education and vocational training
  • Employment, worker management and access to self-employment
  • Access to and enjoyment of essential private services and public services and benefits
  • Law enforcement
  • Migration, asylum and border control management
  • Assistance in legal interpretation and application of the law.

All high-risk AI systems will be assessed before being put on the market and also throughout their lifecycle.

General purpose and generative AI

Generative AI, like ChatGPT, would have to comply with transparency requirements:

  • Disclosing that the content was generated by AI
  • Designing the model to prevent it from generating illegal content
  • Publishing summaries of copyrighted data used for training

High-impact general-purpose AI models that might pose systemic risk, such as the more advanced AI model GPT-4, would have to undergo thorough evaluations and any serious incidents would have to be reported to the European Commission.

Limited risk

Limited risk AI systems should comply with minimal transparency requirements that would allow users to make informed decisions. After interacting with the applications, the user can then decide whether they want to continue using it. Users should be made aware when they are interacting with AI. This includes AI systems that generate or manipulate image, audio or video content, for example deepfakes.

On December 9 2023, Parliament reached a provisional agreement with the Council on the AI act . The agreed text will now have to be formally adopted by both Parliament and Council to become EU law. Before all MEPs have their say on the agreement, Parliament’s internal market and civil liberties committees will vote on it.

More on the EU’s digital measures

  • Cryptocurrency dangers and the benefits of EU legislation
  • Fighting cybercrime: new EU cybersecurity laws explained
  • Boosting data sharing in the EU: what are the benefits?
  • EU Digital Markets Act and Digital Services Act
  • Five ways the European Parliament wants to protect online gamers
  • Artificial Intelligence Act

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ScienceDaily

Early-stage subduction invasion

Our planet's lithosphere is broken into several tectonic plates. Their configuration is ever-shifting, as supercontinents are assembled and broken up, and oceans form, grow, and then start to close in what is known as the Wilson cycle.

In the Wilson cycle, when a supercontinent like Pangea is broken up, an interior ocean is formed. In the case of Pangea, the interior ocean is the Atlantic. This ocean has a rift in the middle, and passive margins on the side, which means no seismic or volcanic activity occurs along its shores. Destined to keep expanding, an Atlantic-type ocean will eventually become the exterior ocean of the next supercontinent. Currently, Earth's exterior ocean is the Pacific. The Pacific also has a rift in the middle, but it is bounded by subduction zones and thus will eventually close. Along its margins, earthquakes and eruptions abound -- a pattern known as the ring of fire.

The ocean-closing phase of each Wilson cycle requires the transition from passive to active (subducting) margins at the edges of the interior ocean. The oceanic crust along the coast of the Atlantic is old and heavy, so it is primed to subduct, but before it can do so, it must break and bend. The only force in nature that can break oceanic plates like these is slab pull from another subduction zone.

But this doesn't happen spontaneously. So how does subduction initiate around interior oceans?

There currently are two subduction zones in the Atlantic: the Lesser Antilles and Scotia. But neither of them formed spontaneously in the Atlantic; they were forced by subduction zones in the Pacific during the Cretaceous and then propagated along transform margins, where the continent is narrow and there is barely a land bridge. They jumped oceans.

Today, on the eastern shore of the Atlantic, in Gibraltar, we have the opportunity to observe the very earliest stages of this process, known as subduction invasion, while the jump occurs from a different basin -- in this case, the Mediterranean.

This is an incredibly valuable opportunity because the chances of observing the very start of any given tectonic process are limited. And subduction initiation is difficult to observe because it leaves almost no traces behind. Once subduction starts, it erases the record of its initial stages; the subducted plate ends up in the mantle, never to be exposed at the surface again (except in the rare case of ophiolites).

The activity of the Gibraltar subduction zone in the Mediterranean has been hotly debated. The Gibraltar arc formed in the Oligocene as a part of the Western Mediterranean subduction zones. While we can see a subducted plate in the mantle underneath it, almost no further movement is currently happening.

A new paper by Duarte et al., just published in Geology , suggests that Gibraltar is active -- it is just currently experiencing a slow movement phase because the subducting slab is very narrow, and it is trying to pull down the entire Atlantic plate.

"[These are] some of the oldest pieces of crust on Earth, super strong and rigid -- if it were any younger, the subducting plate would just break off and subduction would come to a halt," explains Duarte. "Still, it is just barely strong enough to make it, and thus moves very slowly."

A new computational, gravity-driven 3-D model, developed by the authors, shows that this slow phase will last for another 20 million years. After that, the Gibraltar subduction zone will invade the Atlantic Ocean and accelerate. That will be the beginning of the recycling of crust on the eastern side of the Atlantic, and might be the start of the Atlantic itself beginning to close, initiating a new phase in the Wilson cycle.

Broadly, this study shows that subduction invasion, the process whereby a new subduction zone forms in an exterior ocean and then migrates to an interior ocean, is likely a common mechanism of subduction initiation in Atlantic-type oceans, and thus plays a key role in the geological evolution of our planet.

Locally, the finding that the Gibraltar subduction is still currently active has important implications for seismic activity in the area. Recurrence intervals are expected to be very long during this slow phase, but the potential for high-magnitude events, such as the 1755 Lisbon earthquake, remains and requires preparedness.

Much remains to be figured out about the future of the Gibraltar arc. One of the next aspects that Duarte will focus on is determining the exact geometry of the subduction, which will require assessing the relative strength of the nearby continental margins.

  • Earthquakes
  • Natural Disasters
  • Origin of Life
  • Early Humans
  • Lithosphere
  • Plate tectonics
  • Crust (geology)
  • Slash and burn

Story Source:

Materials provided by Geological Society of America . Note: Content may be edited for style and length.

Journal Reference :

  • João C. Duarte, Nicolas Riel, Filipe M. Rosas, Anton Popov, Christian Schuler, Boris J.P. Kaus. Gibraltar subduction zone is invading the Atlantic . Geology , 2024; DOI: 10.1130/G51654.1

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OpenAI Unveils A.I. That Instantly Generates Eye-Popping Videos

The start-up is sharing the new technology, called Sora, with a small group of early testers as it tries to understand the potential dangers.

  • Share full article

essay on evolution of early humans

By Cade Metz

Reporting from San Francisco

In April, a New York start-up called Runway AI unveiled technology that let people generate videos, like a cow at a birthday party or a dog chatting on a smartphone, simply by typing a sentence into a box on a computer screen.

The four-second videos were blurry, choppy, distorted and disturbing. But they were a clear sign that artificial intelligence technologies would generate increasingly convincing videos in the months and years to come.

Just 10 months later, the San Francisco start-up OpenAI has unveiled a similar system that creates videos that look as if they were lifted from a Hollywood movie. A demonstration included short videos — created in minutes — of woolly mammoths trotting through a snowy meadow, a monster gazing at a melting candle and a Tokyo street scene seemingly shot by a camera swooping across the city.

OpenAI, the company behind the ChatGPT chatbot and the still-image generator DALL-E , is among the many companies racing to improve this kind of instant video generator, including start-ups like Runway and tech giants like Google and Meta, the owner of Facebook and Instagram. The technology could speed the work of seasoned moviemakers, while replacing less experienced digital artists entirely.

essay on evolution of early humans

It could also become a quick and inexpensive way of creating online disinformation, making it even harder to tell what’s real on the internet.

“I am absolutely terrified that this kind of thing will sway a narrowly contested election,” said Oren Etzioni, a professor at the University of Washington who specializes in artificial intelligence. He is also the founder of True Media, a nonprofit working to identify disinformation online in political campaigns.

OpenAI calls its new system Sora, after the Japanese word for sky. The team behind the technology, including the researchers Tim Brooks and Bill Peebles, chose the name because it “evokes the idea of limitless creative potential.”

In an interview, they also said the company was not yet releasing Sora to the public because it was still working to understand the system’s dangers. Instead, OpenAI is sharing the technology with a small group of academics and other outside researchers who will “red team” it, a term for looking for ways it can be misused.

essay on evolution of early humans

“The intention here is to give a preview of what is on the horizon, so that people can see the capabilities of this technology — and we can get feedback,” Dr. Brooks said.

OpenAI is already tagging videos produced by the system with watermarks that identify them as being generated by A.I . But the company acknowledges that these can be removed. They can also be difficult to spot. (The New York Times added “Generated by A.I.” watermarks to the videos with this story.)

The system is an example of generative A.I., which can instantly create text, images and sounds. Like other generative A.I. technologies, OpenAI’s system learns by analyzing digital data — in this case, videos and captions describing what those videos contain.

OpenAI declined to say how many videos the system learned from or where they came from, except to say the training included both publicly available videos and videos that were licensed from copyright holders. The company says little about the data used to train its technologies, most likely because it wants to maintain an advantage over competitors — and has been sued multiple times for using copyrighted material.

(The New York Times sued OpenAI and its partner, Microsoft, in December, claiming copyright infringement of news content related to A.I. systems.)

essay on evolution of early humans

Sora generates videos in response to short descriptions, like “a gorgeously rendered papercraft world of a coral reef, rife with colorful fish and sea creatures.” Though the videos can be impressive, they are not always perfect and may include strange and illogical images. The system, for example, recently generated a video of someone eating a cookie — but the cookie never got any smaller.

DALL-E, Midjourney and other still-image generators have improved so quickly over the past few years that they are now producing images nearly indistinguishable from photographs. This has made it harder to identify disinformation online, and many digital artists are complaining that it has made it harder for them to find work.

“We all laughed in 2022 when Midjourney first came out and said, ‘Oh, that’s cute,’” said Reid Southen, a movie concept artist in Michigan. “Now people are losing their jobs to Midjourney.”

Cade Metz writes about artificial intelligence, driverless cars, robotics, virtual reality and other emerging areas of technology. More about Cade Metz

Explore Our Coverage of Artificial Intelligence

News  and Analysis

OpenAI announced that it was releasing a new version of ChatGPT that would remember all prior conversations with users  so it could use that information in future chats. The start-up also unveiled technology that creates videos that look like they were lifted from a Hollywood movie .

The F.T.C. outlawed unwanted robocalls generated by A.I. , amid growing concerns over election disinformation and consumer fraud facilitated by the technology.

Google has released Gemini, a smartphone app that behaves like a talking digital assistant as well as a conversational chatbot .

The Age of A.I.

A year ago, a rogue A.I. tried to break up our columnist’s marriage. Did the backlash that ensued help make chatbots too boring? Here’s how we tame d the chatbots.

Amid an intractable real estate crisis, fake luxury houses offer a delusion of one’s own. Here’s how A.I. is remodeling the fantasy home .

New technology has made it easier to insert digital, realistic-looking versions of soda cans and shampoo on videos on social media. A growing group of creators and advertisers is jumping at the chance for an additional revenue stream .

A start-up called Perplexity shows what’s possible for a search engine built from scratch with A.I. Are the days of turning to Google for answers numbered ?

Chafing at their dependence on the chipmaker Nvidia, Amazon, Google, Meta and Microsoft are racing to build A.I. chips of their own .

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  • Evolution of Human Innovation

Pushing Back Evolutionary Timeline

Evidence of innovation dates to a period when humans faced an unpredictable and uncertain environment, according to three new studies.

The early roots of stone tool innovation, exchange between distant hominin groups, and the use of coloring material are reported in three papers in the journal Science on March 15, 2018. These milestones in the technological, ecological, and social evolution of the human species date back to 320,000 years ago, roughly coinciding with the oldest ages for fossils attributed to Homo sapiens , and 120,000 years earlier than the oldest fossils of our species in eastern Africa. The discoveries include clues to environmental change at the time of these milestones and to the possible factors behind these key developments in human evolution. The publications stem from research in the Olorgesailie Basin, southern Kenya, a multi-decade project of the Smithsonian Institution’s Human Origins Program in collaboration with the National Museums of Kenya. 

Three Olorgesailie Achulean handaxes varying in size from 1.2 millions years ago to 500,000 years ago displayed on the left side of the image. Middle Stone Age Innovations such as points and pigments of varying size and color from 320,000 to 305, 000 years ago displayed on the right side of the image.

The Olorgesailie project is led by Dr. Rick Potts , director of the Smithsonian’s Human Origins Program, National Museum of Natural History, Washington, DC. Potts co-authored the three papers with long-term collaborators Dr. Alison Brooks (George Washington University and the NMNH Human Origins Program), Dr. Alan Deino (Berkeley Geochronology Center), Dr. Kay Behrensmeyer (NMNH), Dr. John Yellen (National Science Foundation and the Human Origins Program) and 19 additional researchers.

A 3/4 aerial view of Locaility B, Olorgesailie Basin in southern Kenya.

The research teams for the three studies published in Science include collaborators from the following institutions: the Smithsonian Institution, the National Museums of Kenya, George Washington University, the Berkeley Geochronology Center, the National Science Foundation, the University of Illinois at Urbana-Champaign, the University of Missouri, the University of Bordeaux (Centre National de la Recherche Scientifique), the University of Utah, Harvard University, Santa Monica College, the University of Michigan, the University of Connecticut, Emory University, the University of Bergen, Hong Kong Baptist University and the University of Saskatchewan.

Funding for this research was provided by the Smithsonian, the National Science Foundation, and George Washington University.

Summary of the papers:

The paper by Alison S. Brooks, John E. Yellen, Richard Potts, and 12 coauthors announces the oldest known evidence of the technology and behaviors linked to the emergence of the human species. The article focuses on early evidence of resource exchange, or trade, between distant groups of ancestral humans, and the use of coloring materials, which is a form of symbolic behavior typical of our species.

Brooks, A.S., Yellen, J.E., Potts, R., Behrensmeyer, A.K., Deino, A.L., Leslie, D.E., Ambrose, S.H., Ferguson, J., d’Errico, F. Zipkin, A.M., Whittaker, S., Post, J., Veatch, E.G., Foecke, K., Clark, J.B., 2018. Long-distance stone transport and pigment use in the earliest Middle Stone Age, Science . http://science.sciencemag.org/cgi/doi/10.1126/science.aao2646

The paper by Richard Potts, Anna K. Behrensmeyer, and 13 coauthors identifies the adaptive challenges during this critical phase in African human evolution. Integrating diverse sources of environmental data, the article advances the idea that changing landscapes and climate throughout the region prompted the evolutionary shift by favoring technological innovation, longer distance movements, and greater connectivity among social groups as a means of adjusting to scarce and unpredictable resources.

Potts, R., Behrensmeyer, A.K., Faith, J.T., Tryon, C.A., Brooks, A.S., Yellen, J.E., Deino, A.L., Kinyanjui, R., Clark, J.B., Haradon, C., Levin, N.E., Meijer, H.J.M., Veatch, E.G., Owen, R.B., Renaut, R.W., 2018. Environmental dynamics during the onset of the Middle Stone Age in eastern Africa, Science . http://science.sciencemag.org/cgi/doi/10.1126/science.aao2200  

The paper by Anna K. Behrensmeyer, Alan Deino and Richard Potts presents the results of more than 15 years of field research on the last 500 thousand years of geological history in the southern Kenya rift system.  The team worked together to integrate the geology, the absolute ages, and the archeological sites to synthesize a detailed history of rapid environmental changes that affected the landscape inhabited by early populations of our genus,  Homo ."

Behrensmeyer, A.K., Potts, R., Deino, A., The Oltulelei Formation of the southern Kenyan Rift Valley: A chronicle of rapid landscape transformation over the last 500 k.y., 2018.  Geological Society of America Bulletin.  https://pubs.geoscienceworld.org/gsa/gsabulletin/article/529628/the-oltulelei-formation-of-the-southern-kenyan

The paper by Alan Deino and 5 coauthors provides the chronology for the discoveries described in the accompanying papers, and documents one of the oldest known and most securely-dated sequences for the African Middle Stone Age, between 320,000 and 295,000 years ago. The article relies on the latest developments in 40 Ar/ 39 Ar dating, integrates U-series analyses carried out at the Berkeley Geochronology Center, and offers a synthesis of dates for late Acheulean and early Middle Stone Age archeological sites throughout Africa.

Deino, A.L., Behrensmeyer, A.K., Brooks, A.S., Yellen, J.E., Sharp, W.D., Potts, R., 2018. Chronology of the Acheulean to Middle Stone Age Transition in Eastern Africa, Science .  http://science.sciencemag.org/content/early/2018/03/14/science.aao2216

Related news:

"A Cultural Leap at the Dawn of Humanity - New finds from Kenya suggest that humans used long-distance trade networks, sophisticated tools, and symbolic pigments right from the dawn of our species"     https://www.theatlantic.com/science/archive/2018/03/a-deeper-origin-of-complex-human-cultures/555674/

"Signs of symbolic behavior emerged at the dawn of our species in Africa"  (great video on this page) http://www.sciencemag.org/news/2018/03/signs-symbolic-behavior-emerged-dawn-our-species-africa

"Ancient climate shifts may have sparked human ingenuity and networking" https://www.sciencenews.org/article/ancient-climate-shifts-may-have-sparked-human-ingenuity-and-networking

"Colored Pigments and Complex Tools Suggest Humans Were Trading 100,000 Years Earlier Than Previously Believed - Transformations in climate and landscape may have spurred these key technological innovations"  https://www.smithsonianmag.com/science-nature/colored-pigments-and-complex-tools-suggest-human-trade-100000-years-earlier-previously-believed-180968499/

“New Understanding of Kenyan Paleoenvironments Opens Window on Human Evolution in the Area"  http://www.geosociety.org/GSA/News/pr/2018/18-10.aspx

“Changing environment influenced human evolution”  http://www.bbc.com/news/science-environment-43401157

“Unstable climate forced early humans to be more social and creative - when times got tough, early humans got craftier, more social, and eventually brainier“  https://www.arstechnica.com/science/2018/03/unstable-climate-forced-early-humans-to-be-more-social-and-creative/

  • Climate Effects on Human Evolution
  • Survival of the Adaptable
  • Human Evolution Timeline Interactive
  • 2011 Olorgesailie Dispatches
  • 2004 Olorgesailie Dispatches
  • 1999 Olorgesailie Dispatches
  • Olorgesailie Drilling Project
  • Kanam, Kenya
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  • Ol Pejeta, Kenya
  • Olorgesailie, Kenya
  • Adventures in the Rift Valley: Interactive
  • 'Hobbits' on Flores, Indonesia
  • Earliest Humans in China
  • Bose, China
  • Anthropocene: The Age of Humans
  • Fossil Forensics: Interactive
  • What's Hot in Human Origins?
  • Instructions
  • Carnivore Dentition
  • Ungulate Dentition
  • Primate Behavior
  • Footprints from Koobi Fora, Kenya
  • Laetoli Footprint Trails
  • Footprints from Engare Sero, Tanzania
  • Hammerstone from Majuangou, China
  • Handaxe and Tektites from Bose, China
  • Handaxe from Europe
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  • Oldowan Tools from Lokalalei, Kenya
  • Olduvai Chopper
  • Stone Tools from Majuangou, China
  • Middle Stone Age Tools
  • Burin from Laugerie Haute & Basse, Dordogne, France
  • La Madeleine, Dordogne, France
  • Butchered Animal Bones from Gona, Ethiopia
  • Katanda Bone Harpoon Point
  • Oldest Wooden Spear
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  • Stone Sickle Blades
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  • Qafzeh: Oldest Intentional Burial
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  • Ishango Bone
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  • Carved Ivory Running Lion
  • Female torso in ivory
  • Ivory Horse Figurine
  • Ivory Horse Sculpture
  • Lady of Brassempouy
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  • Willendorf Venus
  • Ancient Shell Beads
  • Carved Bone Disc
  • Cro-Magnon Shell Bead Necklace
  • Oldest Known Shell Beads
  • Ancient Flute
  • Ancient Pigments
  • Apollo 11 Plaque
  • Carved antler baton with horses
  • Geometric incised bone rectangle
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  • Bison Figurine
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  • One Species, Living Worldwide
  • Human Skin Color Variation
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  • Swartkrans, South Africa
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  • Walking Upright
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  • Humans Change the World
  • Introduction to Human Evolution
  • Nuts and bolts classification: Arbitrary or not? (Grades 6-8)
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  • For College Students
  • Why do we get goose bumps?
  • Chickens, chimpanzees, and you - what do they have in common?
  • Grandparents are unique to humans
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  • The early human tool kit
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  • What can lice tell us about human evolution?
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  • Why do paleoanthropologists love Lucy?
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  • Human Origins Do it Yourself Exhibit
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  • Acknowledgments
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  • Connie Bertka
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  • David Haberman
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  • Members Thoughts on Science, Religion & Human Origins (video)
  • Science, Religion, Evolution and Creationism: Primer
  • The Evolution of Religious Belief: Seeking Deep Evolutionary Roots
  • Laboring for Science, Laboring for Souls:  Obstacles and Approaches to Teaching and Learning Evolution in the Southeastern United States
  • Public Event : Religious Audiences and the Topic of Evolution: Lessons from the Classroom (video)
  • Evolution and the Anthropocene: Science, Religion, and the Human Future
  • Imagining the Human Future: Ethics for the Anthropocene
  • Human Evolution and Religion: Questions and Conversations from the Hall of Human Origins
  • I Came from Where? Approaching the Science of Human Origins from Religious Perspectives
  • Religious Perspectives on the Science of Human Origins
  • Submit Your Response to "What Does It Mean To Be Human?"
  • Volunteer Opportunities
  • Submit Question
  • "Shaping Humanity: How Science, Art, and Imagination Help Us Understand Our Origins" (book by John Gurche)
  • What Does It Mean To Be Human? (book by Richard Potts and Chris Sloan)
  • Bronze Statues
  • Reconstructed Faces

IMAGES

  1. The Evolution Of Humans Essay Sample

    essay on evolution of early humans

  2. Sample English Essay Summary on Evolution

    essay on evolution of early humans

  3. Earliest Humans: Human Evolution, Early Migrations, and Archaeogenetics

    essay on evolution of early humans

  4. Human Evolution: A Timeline of Early Hominids [Infographic]

    essay on evolution of early humans

  5. A Brief Explanation of How Evolution Created Human Culture, essay by

    essay on evolution of early humans

  6. Human Evolution

    essay on evolution of early humans

VIDEO

  1. 🟠EVOLUTION OF HUMANS🟣

  2. The Evolution Of Humans

  3. HISTORY OF HUMAN EVOLUTION 😁 #shortvideo #shorts

  4. UCSP Human Biocultural and Social Evolution Early Humans to the Rise of Civilization

  5. Evolution of humans #shorts

  6. Evolution of Early Humans and Earth

COMMENTS

  1. Human evolution

    Jan. 14, 2024, 7:46 AM ET (Yahoo News) human evolution, the process by which human beings developed on Earth from now-extinct primates. Viewed zoologically, we humans are Homo sapiens, a culture -bearing upright-walking species that lives on the ground and very likely first evolved in Africa about 315,000 years ago.

  2. Introduction to Human Evolution

    Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, between 1.5 million and 1 million years. Species of modern humans populated many parts of the world much later.

  3. The Age of Humans: Evolutionary Perspectives on the Anthropocene

    The ability of early humans to make and use tools, including the control of fire, allowed them to more easily access food by scraping meat off of bones more efficiently, crushing bones for the marrow inside, and obtaining new plant foods such as nutritious tubers and roots from underground. ... The story of human evolution features a unique ...

  4. First humans: Homo sapiens & early human migration (article)

    Homo sapiens, the first modern humans, evolved from their early hominid predecessors between 200,000 and 300,000 years ago. They developed a capacity for language about 50,000 years ago. The first modern humans began moving outside of Africa starting about 70,000-100,000 years ago.

  5. Human Evolution Evidence

    Human Family Tree The human family tree shows the various species that constitute the human evolutionary family. Snapshots in Time In these video interactives, put together clues and explore discoveries the prehistoric sites of Swartkrans, South Africa, Olorgesailie, Kenya, and Shanidar Cave, Iraq.

  6. Introductory essay

    The study of our genetic evolution reveals that as humans migrated from Africa to all continents of the globe, they developed biological and cultural adaptations that allowed for survival in a variety of new environments.

  7. A Brief Account of Human Evolution for Young Minds

    Evolution is the process by which living organisms evolve from earlier, more simple organisms. According to the scientist Charles Darwin (1809-1882), evolution depends on a process called natural selection.

  8. PDF How Evolution Shapes Our Lives: Essays on Biology and Society

    From subtle shifts in the genetic makeup of a single population to the entire tree of life, evolution is the process by which life changes from one generation to the next and from one geological epoch to another. The study of evolution encompasses both the historical pattern of evolu-tion—who gave rise to whom, and when, in the tree of life ...

  9. An Evolutionary Timeline of Homo Sapiens

    15,000 to 40,000 Years Ago: Genetics and Fossils Show Homo sapiens Became the Only Surviving Human Species. A facial reconstruction of Homo floresiensis, a diminutive early human that may have ...

  10. Human Evolution

    Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa. Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago.

  11. A synthesis of the theories and concepts of early human evolution

    1. Introduction Human evolution is characterized by speciation, extinction and dispersal events that have been linked to both global and/or regional palaeoclimate records [ 1 - 7 ]. Many theories have been proposed to link environmental changes to these human evolution events [ 8 - 11 ].

  12. (PDF) Human Evolution: Theory and Progress

    Human evolution refers to the natural process of all human clade members involved in evolutionary history (consisting of Homo and other members of the human tribe, Hominin, after the split...

  13. The influence of evolutionary history on human health and disease

    Genetic disease is a necessary product of evolution (Box 1).Fundamental biological systems, such as DNA replication, transcription and translation, evolved very early in the history of life.

  14. Early Human Migration

    Palaeoanthropologist John Hawks suspects that 'there were many movements and dispersals from Africa and back into Africa, starting much earlier than 2 million years ago and extending up to the most recent.' (Hawks, 12 July 2018).

  15. How scientists perceive the evolutionary origin of human traits

    Invitation to participate in the survey was sent by email to the authors of articles and review papers that had been published in a scientific journal of a relevant field during the three previous years (2010-2012). ... The metabolic cost of walking in humans, chimpanzees, and early hominins. Journal of Human Evolution, 56, 43-54. https ...

  16. Essay on Human Evolution: Top 6 Essays

    Essay # 1. Introduction to Human Evolution: Evolution as a process is composed of two parts: 1. An organism reproducing mechanism that provides variable organisms. Changes to the organism are largely random and effect future generations. They are made without regard to consequences to the organism. 2.

  17. History: Evolution of Humans

    The second picture portrays the world in the third millennium BCE and is related to chapter 2, which describes life in early cities, villages, and pastoral nomads. The map shows that river-basin societies emerged in the basins of large rivers. ... This essay, "History: Evolution of Humans" is published exclusively on IvyPanda's free essay ...

  18. Evolution of the Modern Human

    Australopithecus Around 4 mya the course of evolution gave rise to a new genus, the Australopithecus. "Lucy", the most famous fossil of her kind, shows remnants of chimpanzee in her flexible ankle joints (Richmond and Strait 2000) and small brain size compared to humans (Cameron and Groves 2005).

  19. Evolution Of Humans : Human Biology And Early Culture Essay

    Evolution Of Humans : Human Biology And Early Culture Essay Better Essays 1336 Words 6 Pages Open Document Evolution of Humans No one can be absolutely sure when the first humans actually walked the Earth, only approximations can be made. Approximately 200,000 years ago species are developed in Africa.

  20. Maxwell Ancestors lecture to focus on the early stages of human evolution

    The lecture will be Thursday, Feb. 22 from 6:30 - 8 p.m. at the Hibben Center for Archaeological Research, Room 105, in the Maxwell. The event is free and open to all.

  21. 'Pioneer' Humans Entered Europe Thousands of Years ...

    Additionally, analysis of animal remains revealed that mammals adapted to extreme cold were present at Ranis, including wooly mammoths, reindeer, and wolverines. Analysis of over 1,000 animal bones from Ranis showed that early Homo sapiens processed the carcasses of deer but also of carnivores, including wolves. (Geoff M. Smith) Questions remain about how warm-weather-adapted Homo sapiens ...

  22. Evolution of Human

    The human evolution has gone through several steps. In this essay, the focal point is on the gradual change of the heritable and biological traits of human organisms with emphasis on the difficulties they undergo within the environment. The evolutionary methods give rise to biodiversity at all tiers of human species.

  23. Homo sapiens

    For millions of years all humans, early and modern alike, had to find their own food. They spent a large part of each day gathering plants and hunting or scavenging animals. By 164,000 years ago modern humans were collecting and cooking shellfish and by 90,000 years ago modern humans had begun making special fishing tools. Then, within just the ...

  24. What Is the Difference Between Early Modern Humans and Ancient ...

    Some 300,000 years ago, Homo sapiens split off from a long line of human-ish primates to become the first fully human species, with abilities and ingenuity unrivaled in Earth's history. But back ...

  25. Humans Change the World

    Like early humans, modern humans gathered and hunted food. They evolved behaviors that helped them respond to the challenges of survival. The first modern humans shared the planet with at least three species of early humans. Over time, as modern humans spread around the world, the other three species became extinct.

  26. EU AI Act: first regulation on artificial intelligence

    As part of its digital strategy, the EU wants to regulate artificial intelligence (AI) to ensure better conditions for the development and use of this innovative technology. AI can create many benefits, such as better healthcare; safer and cleaner transport; more efficient manufacturing; and cheaper and more sustainable energy.. In April 2021, the European Commission proposed the first EU ...

  27. Early-stage subduction invasion

    Ancient Retroviruses Played a Key Role in the Evolution of Vertebrate Brains Some Pre-Roman Humans Were Buried With Dogs, Horses and Other Animals By Growing Animal Cells in Rice Grains ...

  28. OpenAI Unveils A.I. That Instantly Generates Eye-Popping Videos

    In April, a New York start-up called Runway AI unveiled technology that let people generate videos, like a cow at a birthday party or a dog chatting on a smartphone, simply by typing a sentence ...

  29. Evolution of Human Innovation

    Based on archeological excavations that began in 2002, the three new studies show that, between 500,000 and 320,000 years ago, early humans in East Africa had begun using color pigments and manufacturing more sophisticated tools than those of the Early Stone Age handaxes, tens of thousands of years earlier than previous evidence has shown in eas...