essay about diversity in living organisms

Diversity In Living Organisms Essay

Diversity in Living Organisms (Science) |Close X | |[pic] Classification And Evolution Classification refers to the identification, naming, and grouping of organisms into a formal system based on similarities in their internal and external structure or evolutionary history. It determines the methods of organizing diversity of life on earth. Therefore, classification helps in understanding millions of life forms in detail. Who started the classification of organisms? Let us explore the history of classification. History of classification One of the earliest schemes of classification was given by the Greek thinker, Aristotle, around 300 BC. He classified animals according to their habitat – land, air, or water. However, this classification …show more content…

This slow change in the body design of an organism over a long period of time is termed as evolution. It helps an organism to survive in its surroundings. Classification allows things to be identified and categorized on the basis of structure and function of an organism, and accordingly, we can refer to them as primitive or advanced organisms. This helps in predicting the line of evolution. Which characteristic do you consider basic – the one that came into existence earlier or later? The characteristic that came into existence earlier is basic because they are independent of other characteristics, in terms of their effects on the structure and function of an organism. For example, cell structure is the basic characteristic that decides the cellularity of an organism that is to be classified. Primitive and advanced organisms A primitive or a lower organism has a simple body structure and an ancient body design or features, which have not changed much over time. An advanced organism or a higher organism has a complex body structure and organization. Thus, we can conclude that unicellular or simple organisms gave rise to multicellular or complex organisms. It means that the existing animals and plants have developed by a process of gradual and continuous change in primitive or simple organisms. This is known as evolution. Which of the following two organisms do you consider primitive? [pic][pic] Amoeba

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The levels consisted in this system would be a cell, tissue, organ, organ system, organism, and the organization of an organism would be a population, community, ecosystem, and finally to the biosphere. A chipmunk lies in the organism level of this structured system. A chipmunk falls in this category because it is alive and contains an organ system. This means that in the chipmunks body there are sets of organs operating to perform certain tasks. There are many major characteristics of life, and frankly, we share the same ones as chipmunks. A few of the 7 characteristic that we share are the ability to grow and change, reproduction, having a reaction to our environment, and a multitude of more correspondences. All in all, it is remarkable to examine the ways that chipmunks are connected with other organisms in the ecosystem based on their level of organization and characteristics of

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Living organisms display specific characteristics. They respond to external stimuli, use energy, reproduce, and contain materials that are only found in living organisms. They sense, adapt, and alter their environment. Living organisms have a high degree of organization and maintain a constant internal environment (Ireland, 2012). These characteristics displayed by a chia pet, however are not displayed by an inanimate object, such as a rock.

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1. Define evolution. There are many parameters and conditions that need to be in place in order for evolution to occur. One such parameter is that the population trait in question must be variable. i.e., there will be variations of a trait found in the population. What are some additional parameters and conditions necessary for evolution to take place?

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Evolution: A heritable change in the characteristics within a population from one generation to the next; the development of new types of organisms from preexisting types of organisms over

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One reason why branch of taxonomy is important for future scientific knowledge is because science is able to distinguish the difference between species. Being able to do distinguish the difference between

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Phylogenetic species concept would be the most expedient and effective process of collecting, naming, and describing what she found. Phylogenetic relies on common ancestry and shared evolutionary when defining a species.

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The purpose of taxonomy is to describe and classify the different types of organisms that roam the continents into groups Genus and species. In biology it’s used to classify organism using latin names and to narrow down 1 organism from Kingdom to species.

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In the Linnaean classification system, all organisms are placed in a ranked hierarchy.   His system was one of small groups building into larger ones. The current groupings of organisms from largest to smallest are kingdom, phylum, class, order, family, genus, and species

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Define evolution? A slow change of something into better form. The word evolution means change, and the process of evolution reflects this definition as it applies to populations of organisms. Biological populations are groups of individuals of the same species that are sub-divided from other populations by geography and are somewhat independent of other groups. Biological evolution, then, is a change in the characteristics of a biological population that occurs over the course of generations. The changes in populations that are considered evolutionary are those that are inherited via genes. Changes that may take place in populations due only to short-term changes in their environment are not

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(2 pt) 2. Use the categories below to list the proper taxa for the organism

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Evolution refers to change over time as species modifies and separate to produce several offspring species.

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ENCYCLOPEDIC ENTRY

Biodiversity.

Biodiversity refers to the variety of living species on Earth, including plants, animals, bacteria, and fungi. While Earth’s biodiversity is so rich that many species have yet to be discovered, many species are being threatened with extinction due to human activities, putting the Earth’s magnificent biodiversity at risk.

Biology, Ecology

grasshoppers

Although all of these insects have a similar structure and may be genetic cousins, the beautiful variety of colors, shapes, camouflage, and sizes showcase the level of diversity possible even within a closely-related group of species.

Photograph by Frans Lanting

Biodiversity is a term used to describe the enormous variety of life on Earth. It can be used more specifically to refer to all of the species  in one region or ecosystem . Bio diversity refers to every living thing, including plants, bacteria, animals, and humans. Scientists have estimated that there are around 8.7 million species of plants and animals in existence. However, only around 1.2 million species have been identified and described so far, most of which are insects. This means that millions of other organisms remain a complete mystery.

Over generations , all of the species that are currently alive today have evolved unique traits that make them distinct from other species . These differences are what scientists use to tell one species from another. Organisms that have evolved to be so different from one another that they can no longer reproduce with each other are considered different species . All organisms that can reproduce with each other fall into one species .

Scientists are interested in how much biodiversity there is on a global scale, given that there is still so much biodiversity to discover. They also study how many species exist in single ecosystems, such as a forest, grassland, tundra, or lake. A single grassland can contain a wide range of species, from beetles to snakes to antelopes. Ecosystems that host the most biodiversity tend to have ideal environmental conditions for plant growth, like the warm and wet climate of tropical regions. Ecosystems can also contain species too small to see with the naked eye. Looking at samples of soil or water through a microscope reveals a whole world of bacteria and other tiny organisms.

Some areas in the world, such as areas of Mexico, South Africa, Brazil, the southwestern United States, and Madagascar, have more bio diversity than others. Areas with extremely high levels of bio diversity are called hotspots . Endemic species — species that are only found in one particular location—are also found in hotspots .

All of the Earth’s species work together to survive and maintain their ecosystems . For example, the grass in pastures feeds cattle. Cattle then produce manure that returns nutrients to the soil, which helps to grow more grass. This manure can also be used to fertilize cropland. Many species provide important benefits to humans, including food, clothing, and medicine.

Much of the Earth’s bio diversity , however, is in jeopardy due to human consumption and other activities that disturb and even destroy ecosystems . Pollution , climate change, and population growth are all threats to bio diversity . These threats have caused an unprecedented rise in the rate of species extinction . Some scientists estimate that half of all species on Earth will be wiped out within the next century. Conservation efforts are necessary to preserve bio diversity and protect endangered species and their habitats.

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Module 1: Introduction to Biology

The diversity of life, learning outcomes.

• Explain the “diversity of life”

Figure 1. Life on earth is incredibly diverse.

Biological diversity is the variety of life on earth. This includes all the different plants, animals, and microorganisms; the genes they contain; and the ecosystems they form on land and in water. Biological diversity is constantly changing. It is increased by new genetic variation and reduced by extinction and habitat degradation.

What Is Biodiversity?

Biodiversity refers to the variety of life and its processes, including the variety of living organisms, the genetic differences among them, and the communities and ecosystems in which they occur. Scientists have identified about 1.9 million species alive today. They are divided into the six kingdoms of life shown in Figure 2. Scientists are still discovering new species. Thus, they do not know for sure how many species really exist today. Most estimates range from 5 to 30 million species.

Figure 2. Click for a larger image. Known life on earth

Cogs and Wheels

To save every cog and wheel is the first precaution of intelligent tinkering. —Aldo Leopold, Round River: from the Journals of Aldo Leopold , 1953

Leopold—often considered the father of modern ecology—would have likely found the term biodiversity  an appropriate description of his “cogs and wheels,” even though the idea did not become a vital component of biology until nearly 40 years after his death in 1948.

Literally, the word biodiversity  means the many different kinds ( diversity ) of life ( bio -), or the number of species in a particular area.

• The most precise and specific measure of biodiversity is genetic diversity or genetic variation within a species. This measure of diversity looks at differences among individuals within a population, or at difference across different populations of the same species.
• The level just broader is  species diversity , which best fits the literal translation of biodiversity : the number of different species in a particular ecosystem or on Earth. This type of diversity simply looks at an area and reports what can be found there.
• At the broadest most encompassing level, we have ecosystem diversity . As Leopold clearly understood, the “cogs and wheels” include not only life but also the land, sea, and air that support life. In ecosystem diversity, biologists look at the many types of functional units formed by living communities interacting with their environments.

Although all three levels of diversity are important, the term biodiversity usually refers to species diversity!

Video Review

Watch this discussion about biodiversity:

You can view the transcript for “Biodiversity from ‘the Wild Classroom'” here (link opens in new window).

Biodiversity provides us with all of our food. It also provides for many medicines and industrial products, and it has great potential for developing new and improved products for the future. Perhaps most importantly, biological diversity provides and maintains a wide array of ecological “services.” These include provision of clean air and water, soil, food and shelter. The quality—and the continuation— of our life and our economy is dependent on these “services.”

Australia’s Biological Diversity

Figure 2. The short-beaked echidna is endemic to Australia. This animal—along with the platypus and three other species of  echidnas—is one of the five surviving species of egg-laying mammals.

The long isolation of Australia over much of the last 50 million years and its northward movement have led to the evolution of a distinct biota. Significant features of Australia’s biological diversity include:

• over 80% of flowering plants
• over 80% of land mammals
• 88% of reptiles
• 45% of birds
• 92% of frogs
• Wildlife groups of great richness. Australia has an exceptional diversity of lizards in the arid zone, many ground orchids, and a total invertebrate fauna estimated at 200,000 species with more than 4,000 different species of ants alone. Marsupials and monotremes collectively account for about 56% of native terrestrial mammals in Australia.
• Wildlife of major evolutionary importance. For example, Australia has 12 of the 19 known families of primitive flowering plants, two of which occur nowhere else. Some species, such as the Queensland lungfish and peripatus, have remained relatively unchanged for hundreds of millions of years.

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Diversity in Living Organisms

What is diversity in living organisms.

Biodiversity is used to define the diversity of life forms worldwide. It is a word that is used more often to refer to the classification of living species found in a particular geographic region. The Diversity of living species of a geographic region in an area provides stability in the respective region.

There are numerous living organisms on earth with different sizes, shapes, habitats, nutrition, reproduction, and more.  That depends on their physical features and their habitat. Animals of any kingdom are classified into different orders and classes.

Animals live in different climates like water, land, grasslands, deserts, forests, ice, water, and ice to forests, deserts, and grasslands. All these organisms consist of cells.

Cells are one of the essential characteristics of living organisms.  Cells are structural units of life. It carries out specifically assigned functions in living species.  In this way, a group of cells from tissue in living species.

Diversity in living organisms can be seen everywhere on earth.  The region of the earth is highly diverse and is called the region of mega biodiversity. Twelve countries in the world have more than half of the biodiversity in the world. India is also one of them.

Over millions of years, diversity has been going on in living beings.  Species have evolved from ape-like beings to homo sapiens.  People look for similarities between organisms to classify them, and hence they study them as a whole. Regarding this, fundamental characteristics need to be decided, which would form the foundation for classifying.

Introduction to Diversity in Living Organisms

Life exists in different forms on Earth. When it comes to the question of the number of living organisms found on the earth, the answer is unimaginable. This is so because of the large diversity of organisms continuously evolving into a different variety ever since the origin of life had taken place. Diversity is present at different levels like genetic diversity, species diversity, and ecological diversity. Mango alone has around 10,000 varieties in India. This alone example indicates how large and diverse are the living organisms. Gaining knowledge about this large diversity is impossible without classifying them. Thus classification becomes an important step towards the study of different organisms found on the earth.

Biological Classification

The process of putting all the organisms in certain groups on the basis of certain similarities and differences is known as Classification

Various characteristics are taken into account in order to classify an organism. Some of them are-

The type of cell present whether the organism is having a eukaryotic cell or a prokaryotic cell. 

The number of cells whether the organism is unicellular or multicellular.

Body organization whether the organization is cellular, tissue-level, or organ-level.

 The nutrition of organisms whether it's autotrophic or heterotrophic.

Morphological features of the organisms.

Anatomical features of the organism etc.

All these features including many others are taken into consideration during the classification

Classification System

Various scientists have proposed their own model of classifying organisms. Some of these are given below.

Two Kingdom Classification

Carolus Linnaeus gave the 2-kingdom system of classification and divided all the organisms into two groups as Plantae and Animalia. This kind of classification brought all the organisms which had a cell wall together within their cell in one group called the Plantae and the rest all were placed in the other group known as Animalia.

Plantae comprises bacteria, fungi with plants. All were very different from each other but still were kept together under two-kingdom classification. There was no distinction between the prokaryotes as well as eukaryotes. Thus this system of classification was not right but surely helped in evolving a better classification system.

Five Kingdom Classification

R.H Whittaker proposed a five-kingdom classification. This classification is accepted and corrected worldwide. A number of criteria were considered for making this model like the cell type, cell number, cell organization, nutrition, etc. 

It consists of 5 groups /kingdoms 

Animalia 

Characteristics of Five Kingdom

Kingdom Monera

This kingdom has organisms that are unicellular and have prokaryotic cell.

It includes bacteria, cyanobacteria, etc.

Their cell usually has a cell wall.

They can be autotrophic or heterotrophic.

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Kingdom Protista

This kingdom includes organisms that are also unicellular but have a eukaryotic cell.

They may be photosynthetic or heterotrophic.

They may possess structures like flagella and cilia.

Examples are amoeba, euglena, paramecium, etc.

Kingdom Fungi

This is the first kingdom with multicellular organisms.

They exhibit a heterotrophic mode of nutrition more specifically saprotrophic mode of nutrition.

They have a eukaryotic cell with a cell wall that is made up of chitin.

Example - yeast, mushroom

Kingdom Plantae

All organisms are eukaryotic and multicellular.

The body can be seen as differentiated into higher groups.

They are photosynthetic and exhibit an autotrophic mode of nutrition. Some members are partially heterotrophic.

Their cell has a cell wall made up of cellulose.

Examples- mango tree, red algae , etc.

Kingdom Animalia

All members are eukaryotic and multicellular.

Their cells lack a cell wall.

They are heterotrophs.

Examples- lion, dog, fish, etc.

Classification Hierarchy

The broadest group Kingdom is further divided into small groups to reach a point of maximum similarity in one group of organisms. Thus a hierarchy of classification is developed when the small groups are arranged from the lowest to the highest order. Each category in the hierarchy is known as Taxon.

Following is the Hierarchy of Classification:

Phylum / Division

 Genus

Species are the basic unit of classification.

Classification and Evolution

Classification of organisms is related to evolution. Evolution is the change that takes more over the years in the body design of organisms for better survival. Charles Darwin first described the concept of evolution in his book ‘The Origin Of Species’ in 1859.

Lower organisms are the organisms that seem to have not changed over the years.

Higher organisms are relatively recent and have their particular body designs.

Diversity in Living Organisms is a fundamental topic introduced in students in higher and junior classes.  It is a primary and essential topic of Study, for this one can easily follow Vedantu and know about interesting facts about Diversity.

Yeast is the only unicellular fungus.

Lichens are organisms in which algae and fungi live together and exhibit symbiotic relationships.

FAQs on Diversity in Living Organisms

1. Why is there diversity among organisms? 

Calculation of biology is never perfect, and one can not achieve the exact copy. There are numerous steps in molecular biology that do not give the exact copy from replication to a functional protein. This incident leads to mutation, changes, and Diversity. This Diversity is then screened by natural selection. Whoever survives the present environmental condition will reproduce if naturally selected as per evolution.

2. Why is biodiversity so important?

Biodiversity refers to the number of different species living in the regions.  It represents the wealth of biological wealth in nature. It globally varies with the regions. Many natural factors affect biodiversities like temperature, soils, and other natural things. It maintains the balance of climate and nature in a recycled way. Biodiversity also affects social life like recreation, education, research, human health, industry, and culture. Thus one can say that biodiversity is crucial for the well-being of life on earth.

3. Why does evolution result in so much biodiversity?

The earth is much bigger than we can think. There are lots of species that are still not discovered. They also survive in various possible ways by fighting with nature. There are many attainable ways for organisms to survive.  A planet has its way to protect the lives in it.  There are several chemicals set up to make them survive. And this is also getting evolved day by day in their need.

4. Describe the significance of the study of living organisms for students?

Most people believe that everyone must study living organisms as humans are also part of evolution. By studying, one can know detailed information about nature, from recycling every natural thing and the life of every living species. There are many things about what a person may know. It is also an essential part for students as they should know about the Living species in nature. Diversity is now included in the study syllabus of the students.

5. How can a student get to know detailed information about living organisms?

The biodiversity of living organisms is a critical topic for students. If any student wants to know about that from the internet, they can find many research materials, and there are thousands of results and online learning websites where one can get help in any subject or topic. But choosing the best is the priority.

6. Comment on the relationship between classification and evolution.

As we take a closer look at the classification of organisms and how the kingdoms and phyla are arranged one after the other, depicting a change from simple to complex forms,  it actually indicates the pattern of evolution that has taken place on the earth in the past years. Classification and its hierarchy is the direct evidence of evolution. Higher groups are evolved from the lower groups from gradual evolution and these groups are placed accordingly in the hierarchy. Thus Classification is interrelated to evolution though were developed and studied independently.

7. Define the artificial system of classification.

Organisms were also classified on the basis of habitat and feeding habits are known as an artificial system of classification.

Some groups on the basis of habitats are mentioned below :

Aquatic- Organisms that live in water are considered aquatic organisms. It has many other subgroups like Benthos (bottom-dwelling), sedentary (fixed in water), etc.

Terrestrial- Organisms that live on land are known as terrestrial. They can be scansorial (wall climbers), arboreal (tree climbers), cursorial (fast-moving ), etc. Example- ants, monkeys, etc.

Amphibious- These types of organisms can live both on land and water. Example- Frog and Crocodile.

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1.6: The Origins, Evolution, Speciation, Diversity and Unity of Life

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• Page ID 16413

• Gerald Bergtrom
• University of Wisconsin-Milwaukee

The question of how life began has been with us since the beginnings or recorded history. It is now accepted that there was a time, however brief or long, when the earth was a lifeless (prebiotic) planet. Life’s origins on earth date to some 3.7-4.1 billion years ago under conditions that favored the formation of the first cell, the first entity with all of the properties of life. But couldn’t those same conditions have spawned multiple cells independently, each with all of the properties of life? If so, from which of these did life, as we know it today, descend? Whether there were one or more different “first cells”, evolution (a property of life) only began with those cells.

115 Properties of Life

The fact that there is no evidence of cells of independent origin may reflect that they never existed. Alternatively, the cell we call our ancestor was evolutionarily successful at the expense of other life forms, which thus became extinct. In any event, whatever this successful ancestor may have looked like, its descendants would have evolved quite different appearances, chemistries and physiologies. These descendant cells would have found different genetic and biochemical solutions to achieving and maintaining life’s properties. One of these descendants evolved the solutions we see in force in all cells and organisms alive today, including a common ( universal ) genetic code to store life’s information, as well as a common mechanism for retrieving the encoded information. Francis Crick called is commonality the “Central Dogma” of biology. That ancestral cell is called our Last Universal Common Ancestor , or LUCA .

116 The Universal Genetic Code 117 Origins of Life 118 Life Origins vs Evolution

Elsewhere we consider in more detail how we think about the origins of life. For now, our focus is on evolution, the property of life that is the basis of speciation and life’s diversity.

Natural selection was Charles Darwin’s theory for how evolution led to the structural diversity of species. New species arise when beneficial traits are naturally selected from genetically different individuals in a population, with the concomitant culling of less fit individuals from populations over time. If natural selection acts on individuals, evolution results from the persistence and spread of selected, heritable changes through successive generations in a population. Evolution is reflected as an increase in diversity and complexity at all levels of biological organization, from species to individual organisms to molecules. For an easy read about the evolution of eyes (whose very existence according to creationists could only have formed by intelligent design by a creator), see the article in National Geographic by E. Yong (Feb., 2016, with beautiful photography by D. Littschwager).

Repeated speciation occurs with the continual divergence of life forms from an ancestral cell through natural selection and evolution. Our shared cellular structures, nucleic acid, protein and metabolic chemistries (the ‘unity’ of life) supports our common ancestry with all life. These shared features date back to our LUCA! Most living things even share some early behaviors . Take our biological clock , an adaptation to our planet’s 24 hour daily cycles of light and dark that have been around since the origins of life; all organisms studied so far seem to have one!. The discovery of the genetic and molecular underpinnings of circadian rhythms (those daily cycles) earned Jeffrey C. Hall, Michael Rosbash and Michael W. Young the 2017 Nobel Prize in Medicine or Physiology (click Molecular Studies of Circadian Rhythms wins Nobel Prize to learn more)!

The molecular relationships common to all living things largely confirm what we have learned from the species represented in the fossil record. Morphological, biochemical and genetic traits that are shared across species are defined as homologous , and can be used to reconstruct evolutionary histories. The biodiversity that scientists (in particular, environmentalists) try to protect is the result of millions of years of speciation and extinction. Biodiversity needs protection from the unwanted acceleration of evolution arising from human activity, including blatant extinctions (think passenger pigeon), and near extinctions (think American bison by the late 1800s). Think also of the consequences the introduction of invasive aquatic and terrestrial species and the effects of climate change.

Let’s look at the biochemical and genetic unity among livings things. We’ve already considered what happens when cells get larger in evolution when we tried to explain how larger cells divided their labors among smaller intracellular structures and organelles. When eukaryotic cells evolved into multicellular organisms, it became necessary for the different cells to communicate with each other and to respond to environmental cues.

Some cells evolved mechanisms to “talk” directly to adjacent cells and others evolved to transmit electrical (neural) signals to other cells and tissues. Still other cells produced hormones to communicate with cells to which they had no physical attachment. As species diversified to live in very different habitats, they also evolved very different nutritional requirements, along with more extensive and elaborate biochemical pathways to digest their nutrients and capture their chemical energy. Nevertheless, despite billions of years of obvious evolution and astonishing diversification, the underlying genetics and biochemistry of living things on this planet is remarkably unchanged. Early in the 20th century, Albert Kluyver first recognized that cells and organisms vary in form appearance in spite of the essential biochemical unity of all organisms (see Albert Kluyver in Wikipedia ). This unity amidst the diversity of life is a paradox of life that we will probe further in this course.

A. Genetic Variation, the Basis of Natural Selection

DNA contains the genetic instructions for the structure and function of cells and organisms. When and where a cell or organism’s genetic instructions are used (i.e., to make RNA and proteins) are regulated. Genetic variation results from random mutations. Genetic diversity arising from mutations is in turn, the basis of natural selection during evolution.

119 The Random Basis of Evolution

B. The Genome: An Organism’s Complete Genetic Instructions

We’ve seen that every cell of an organism carries the DNA including gene sequences and other kinds of DNA. The genome of an organism is the entirety of its genetic material (DNA, or for some viruses, RNA). The genome of a common experimental strain of E. coli was sequenced by 1997 (Blattner FR et al. 1997 The complete genome sequence of Escherichia coli K-12. Science 277:1452-1474). Sequencing of the human genome was completed by 2001, well ahead of the predicted schedule (Venter JC 2001 The sequence of the human genome . Science 291:1304-1351). As we have seen in the re-classification of life from five kingdoms into three domains, nucleic acid sequence comparisons can tell us a great deal about evolution. We now know that evolution depends not only on gene sequences, but also, on a much grander scale, on the structure of genomes. Genome sequencing has confirmed not only genetic variation between species, but also considerable variation between individuals of the same species. Genetic variation within species is in fact the raw material of evolution. It is clear from genomic studies that genomes have been shaped and modeled (or remodeled) in evolution. We’ll consider genome remodeling in more detail elsewhere.

C. Genomic ‘Fossils’ Can Confirm Evolutionary relationships.

It had been known for some time that gene and protein sequencing could reveal evolutionary relationships and even familial relationships. Read about an early demonstration of such relationships based on amino acid sequence comparisons across evolutionary time in Zuckerkandl E and Pauling L. (1965) Molecules as documents of evolutionary theory. J. Theor. Biol. 8:357-366. It is now possible to extract DNA from fossil bones and teeth, allowing comparisons of extant and extinct species. DNA has been extracted from the fossil remains of humans, other hominids, and many animals. DNA sequencing reveals our relationship to each other, to our hominid ancestors and to animals from bugs to frogs to mice to chimps to Neanderthals to… Unfortunately, DNA from organisms much older than 10,000 years is typically so damaged or simply absent, that relationship building beyond that time is impossible. Now in a clever twist, using what we know from gene sequences of species alive today, investigators recently ‘constructed’ a genetic phylogeny suggesting the sequences of genes of some of our long-gone progenitors, including bacteria (click here to learn more: Deciphering Genomic Fossils ). The comparison of these ‘reconstructed’ ancestral DNA sequences suggests when photosynthetic organisms diversified and when our oxygenic planet became a reality.

120 Genomic Fossils- Molecular Evolution

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8 Evolution and Diversity

Evolution and diversity result from the interactions between organisms and their environments and the consequences of these interactions over long periods of time. Organisms continually adapt to their environments, and the diversity of environments that exists promotes a diversity of organisms adapted to them. In recent years, new techniques and approaches have opened exciting new avenues of investigation of the processes that generate evolution and diversity. As a result, greater opportunities exist now for advancing knowledge than during any period since the 1930s and 1940s, when evolutionary biology and genetics became united in what came to be called the modem synthesis of evolutionary biology.

• The Processes and Results of Evolution Are Exemplified in the Evolution of Insecticide Resistance in Insects and Antibiotic Resistance in Bacteria

The first synthetic organic insecticide to be adopted for practical use was DDT, which was introduced in 1941. DDT appeared to have many advantages because, in proper dose, it was toxic to insects but not to humans. As a consequence, DDT was quickly employed worldwide to control houseflies, mosquitoes, and a variety of other insect pests. After the initial success of DDT, many other exotic chemical compounds were introduced as insecticides. The introduction and widespread use of each of these was quickly followed by the evolution of resistance in large numbers of insect species. In fact, more than 200 species of insects had become resistant to DDT by 1976; some species have evolved multiple resistance to four or more groups of chemical insecticides.

In many cases, the insecticide resistance results from the action of a single gene, although multiple other genetic changes that can modify the response to insecticides also occur. In the common housefly, resistance results from the presence of an enzyme called DDTase, the natural function of Which is unknown. Mutant forms of the enzyme convert DDT into the relatively harmless compound DDE. Resistance in the mosquito Aedes aegypyti is also associated with a DDTase enzyme, but not the one found in the housefly.

The evolution of resistance to insecticides is so common because the insect populations often contain rare mutant variants that are already resistant. Exposure to the insecticide gives an advantage to these mutants, and over several generations, they gradually increase in frequency at the expense of the normal types until very few of the normal sensitive types remain.

A remarkable principle in population genetics states that insecticide resistance can be expected to evolve in approximately 5 to 50 pest generations, irrespective of the insect species, geographical region, nature of the pesticide, frequency and method of application, and other seemingly important variables. The phenomenon occurs because the time required to evolve significant resistance depends on the logarithm of the total increase in frequency of the resistance gene as a result of the pesticide application, which over a wide range of realistic values is effectively limited to 5 to 50 generations. The rapid, repeated evolution of insecticide resistance in many parts of the world reflects the operation of this simple mathematical principle.

A similar situation accounts for the repeated evolution of antibiotic resistance in bacteria: Rare bacterial types containing genes for resistance are favored in the presence of the antibiotic and eventually displace the normal sensitive types. In this case, the overuse of inexpensive antibiotics, not only in medicine but in animal feed, fish culture, and agriculture, has promoted the evolution of antibiotic resistance in a wide spectrum of microorganisms. In many cases, the resistance genes are contained in mobile genetic elements that can be transmitted from one organism to the next, and their spread has resulted in the wide dissemination of the resistance genes among pathogenic and nonpathogenic forms.

The molecular evolution of antibiotic resistance is similar to the process that bacteria have used for millenia to evolve resistance to naturally occurring antibiotics and to soil contaminated with lethal concentrations of heavy metals. A resistance gene that evolves in one bacterial species can potentially be disseminated to many others by means of molecules known as plasmids, which are transmitted among suitable hosts by cell contact. These plasmids occasionally pick up transposable DNA sequences that contain genes resistant to antibiotics, and they confer resistance upon host cells. When the antibiotics are widely used and present in the environment, cells containing the resistance plasmids are favored, and the plasmid spreads. In many cases resistance plasmids have acquired genes for simultaneous resistance to five or more chemically unrelated antibiotics. For some pathogenic bacteria, such as gonorrhea, antibiotic resistance has become so widespread that clinical treatment is severely compromised.

The evolution of insecticide resistance in insect populations, antibiotic resistance in microbial populations, herbicide resistance in plant populations, and heavy-metal tolerance in plant and bacterial populations has been demonstrated repeatedly. In every case, genetic variation and natural selection provide an amazingly effective process for promoting the adaptation of organisms to their environments. The study of evolution and diversity of life on earth is concerned with the tempo, mode, and patterns of such adaptations.

EVOLUTION OF INSECTICIDE RESISTANCE

Some of the most dramatic examples of evolution in action result from the natural selection for chemical pesticide resistance in natural populations of insects and other agricultural pests. In the 1940s, when chemical pesticides were first applied on a large scale, an estimated 7 percent of the agricultural crops in the United States were lost to insects. Initial successes in chemical pest management were followed by a gradual loss of effectiveness. Today, more than 400 pest species have evolved significant resistance to one or more pesticides, and 13 percent of the crop of yields in the United States is lost to insects.

In many cases, significant pesticide resistance has evolved in 5 to 50 generations in spite of great variation in the insect species, the insecticide, and the method of application. Theoretical population genetics helps us understand this apparent paradox. Many of the insecticide resistances result from single mutant genes. The resistance genes are often partially dominant, so the change in the frequency of the resistance gene is governed approximately by the equation

in which p and q are, respectively, the gene frequencies of the resistant and sensitive genes, initially (time 0) and at time t generations after insecticide application, and s measures the degree to which resistant insects are favored over sensitive ones.

Prior to application of the pesticide, the gene frequency p 0 of the resistant mutation is generally close to 0. Application of the pesticide increases the gene frequency, sometimes by many orders of magnitude, but significant resistance is noticed in the pest population even before the gene frequency p 1 increases above a few percent. Thus, as rough approximations, we may assume that q 0 and q 1 are both close enough to 1 that In( p 0 / q 0 ) = In( p 0 ) and In( p 1 / q 1 ) = In( p 1 ). Using these approximations, the equation implies that t = (2/ s ) In( p 1 / p 0 ). In many cases, the ratio p 1 / p 0 may range from 1 × 10 2 to perhaps 1 × 10 7 , and s may typically be 0.5 or greater. Over this wide range of parameter values, time t is effectively limited to 5 to 50 generations for the appearance of a significant degree of pesticide resistance. Details in actual cases will depend on such factors as the size of the insect population and the extent of genetic isolation between local populations, and the evolution of polygenic resistance may be expected to take somewhat longer than single-gene resistance. Nevertheless, the example demonstrates the predictive power of mathematical approaches in evolutionary biology.

• Some of the Most Exciting Current Research Opportunities in Evolution and Diversity Result from Technical Innovations in Molecular Biology

The techniques of molecular biology have revealed a rich level of detail in studies of DNA variation and its analysis. They have uncovered an unexpected avenue of genomic evolution through the activities of transposable elements. They have opened up the transfer of individual genes between species as a major new tool for the study of the mechanisms and subsequent events in speciation. And they have made possible an integration of the techniques of molecular biology with questions of field natural history, such as in the use of mitochondrial DNA polymorphisms to study population structure and migration in fish and other organisms.

Application of the techniques of molecular biology has made possible, for the first time, the beginnings of a synthesis of microbiology and evolutionary biology. These two fields have developed in almost complete isolation from each other. Microbiology is among the least evolutionarily oriented of biological disciplines, and evolutionary biology is the evolutionary biology of metazoans. Studies at the interface of these disciplines will result in the definition of new evolutionary principles and a deeper understanding of principles already established. Perhaps the most surprising initial result of studies in microbial evolution has been the discovery of what some scientists regard as a distinct kingdom of organisms, the archaebacteria, which combine some features of more familiar kinds of bacteria (eubacteria) with others characteristic of eukaryotic organisms.

Indeed, paleobiologists now believe that the earth's biota was composed solely of bacteria for at least two-thirds of its total history. Many evolutionary innovations have been powered by changes in intracellular biochemistry rather than by changes in the shape, size, or physical organization of organisms. Moreover, the global biota, especially bacteria, with their diverse physiological capabilities, have interacted with and changed the global environment in numerous crucial ways, such as in the creation of our oxygen-rich atmosphere.

The application of molecular techniques has also contributed to the current revolution in systematics. Molecular studies of DNA and proteins are now used routinely to distinguish species and to estimate phylogenetic relations among closely related species. Direct DNA sequencing is providing phylogenetically useful data almost faster than they can be analyzed. The inferred genealogical relations based on macromolecules are usually consistent with those based on morphology, but molecular studies often help to resolve relations that are morphologically ambiguous.

Overall similarity in macromolecules provides a reliable measure of evolutionary time only when the molecules being studied evolve at much the same rate in different lineages and at different times. Whether DNA sequences actually evolve with regular rates like molecular clocks is still much debated, but the data so far suggest at least moderate regularity. The concept of the molecular clock has provided a unique and powerful time dimension in evolutionary studies and has augmented as well as complemented inferences from the fossil record. However, not all of the evidence is consistent with the hypothesis that molecular evolution occurs at a nearly constant rate, and further evidence is needed to establish the validity of the hypothesis and to determine its range of application.

The explosive increase in knowledge of DNA sequences has created an acute need for new kinds of computational technologies and algorithms, as well as new statistical approaches, so that the data can be interpreted to maximum advantage. Appropriately analyzed, the new kinds of data will reveal, with a level of detail never before possible, patterns in the history of evolution; the new data will thus shed light not only on the evolution of macromolecules, but also on the processes of evolution of morphology, life histories, and physiology. Regrettably, the analysis of sequence data, which must bring together experts in statistics, computer science, mathematics, molecular biology, population genetics, developmental biology, and systematics, has lagged behind as ever more data have accumulated. At the same time, more extensive data on the extent of DNA sequence variation within species are badly needed.

• Technical Innovations That Have Transformed Studies of Evolution and Diversity Are Not Limited to Molecular Biology

Studies in biomechanics, ecology, and behavior have profited tremendously from improved techniques of photography and telemetry, and in almost every area of study, modern computers facilitate sophisticated simulation modeling and data analysis. Paleobiology has benefited from methods of organic geochemistry that enable the determination of the nature and isotopic characteristics of biologically derived organic compounds preserved in ancient sediments and also from new techniques of radiometric age determination and new data regarding the geologic and plate-tectonic history of the earth. These approaches, when combined with information derived from molecular biology, promise to promote new knowledge about such fundamental evolutionary events as the origin of invertebrates, vertebrates, plants, and human beings. Even earlier Precambrian events, such as the advent of photosynthesis, oxygen-dependent respiration, nucleated cells, eukaryotic sexual reproduction, and the modern type of anaerobic-aerobic global environment, may be within the reach of the new approaches.

Progress in the study of evolution and diversity does not require technical innovations, although it frequently benefits from them. Advances also come from the synthesis of previously disconnected areas, from new ways of looking at problems, or from new concepts. Therefore, in evolution and diversity, too much stress on technical virtuosity and trendiness runs the risk of promoting a kind of brush-fire pattern of scientific advance, with great activity and excitement near the front but little behind in the area where the practical applications of basic discoveries are often developed.

Although many exciting directions in evolution and diversity have been opened by advances in molecular biology, numerous fundamental problems occur at levels of biological organization above that of molecules. The evolution of populations of organisms is affected by the interactions with the environment of physiology, development, and behavior at levels that are not amenable to molecular analysis. Molecular biology is an aid but not a panacea in the discovery and classification of organisms. And the processes of speciation and extinction, while fundamental to evolution and diversity, are population, not molecular, processes.

• The Evolutionary Process

Population Genetics Continues to Emphasize Genetic Variation — Its Nature, Causes, and Maintenance in Populations

Studies of population genetics or genetic variation have become significantly more sophisticated with the use of molecular techniques and new types of material, including microbial organisms and chloroplast and mitochondrial DNA. Progress in molecular biology has been especially helpful for population genetics and promises to aid in the resolution of several outstanding problems in the field. Genetic variation can be resolved at the ultimate level of the DNA sequence. With this level of resolution, it becomes possible to determine whether genes that are highly variable within populations also evolve rapidly. The distribution of DNA polymorphisms within and among species results from the operation of evolutionary forces that are in many cases too weak or too difficult to measure in the laboratory or field; it may be possible to infer their magnitude from analysis of the sequences themselves. The rich possibilities of inferences that may be made from DNA sequence data warrant significant efforts in this direction.

The Technique of Site-Directed Mutagenesis Also Opens New Possibilities for Population Genetics

Traditionally, inferences about evolutionary constraints on molecular structure have been gathered from comparisons of homologous molecules among species. With site-directed mutagenesis, the inferences can be tested directly by deliberately altering parts of the molecule of interest, reintroducing the gene for the altered molecule into living organisms, and studying the effects of the changes. Such experiments reveal not only which changes affect the molecule, but also the magnitude of these effects. For the first time, population geneticists are able to study a collection of mutant molecules that are well characterized at the molecular level.

DNA SEQUENCES IN EVOLUTIONARY STUDIES

Comparisons of DNA and protein sequences have revolutionized the reconstruction of the evolutionary relations among organisms because the sequences themselves contain information about their ancestral history that can be extracted by appropriate statistical methods. Equally powerful inferences can be drawn from comparisons of sequences among individuals within species. This is possible because the sequences also contain information about the evolutionary forces that molded them, which can be studied to make inferences about the magnitude of natural selection, the importance of random processes, the role of recombination, and so on.

Two studies of DNA sequences among natural isolates of the bacterium Escherichia coli underscore the power of the molecular approach. One study focused on DNA sequences in the gnd gene, which codes for the enzyme 6-Phosphogluconate dehydrogenase. The purpose was to estimate the fraction of observed amino acid polymorphisms that are selectively neutral. This has been a central issue in population genetics for more than a decade, but it has defied resolution because most statistical tests of observed gene frequencies and most laboratory experiments lack sufficient power to detect selection coefficients of the relevant magnitude. Although most random amino acid substitutions might be expected to be harmful, only a small proportion of harmful mutations ever become established as polymorphisms in natural populations. A significant proportion of alleles that become polymorphic might therefore be expected to be selectively or nearly neutral.

The idea behind the study of DNA sequences is that nucleotide polymorphisms at silent sites, which do not change amino acid sequences, can be used as internal standards for comparison with amino acid polymorphisms in the same gene. When 768 nucleotides in the gnd gene in seven strains of E. coli were compared, 12 amino acid polymorphisms and 78 silent polymorphisms were found. All 12 amino acid polymorphisms occurred in singleton configurations (meaning that six strains shared a common amino acid at the site and only one strain was different), whereas only about half of the silent polymorphisms exhibited this configuration. Based on this difference alone, one can conclude the no more than six of the amino acid substitutions could be selectively neutral. Alternatively, if all amino acid polymorphisms are assumed to be mildly harmful, the amount of selection necessary to account for the preponderance of singleton configurations is only about 1.6 × 10 -7 , an amount of selection much too small to detect except by means of DNA sequence comparisons.

The second study concerned the occurrence of genetic recombination among natural isolates of E. coli . Evidence for recombination was found in a region of 1,871 nucleotide pairs around the phoA gene, which codes for alkaline phosphatase, in 10 natural isolates. The region contained 87 polymorphic nucleotide sites, of which 42 were shared by two or more strains. Comparisons of the shared polymorphisms gave clear evidence for intragenic recombination in that polymorphic nucleotides common to two or more strains tended to be spatially clustered within the gene. The putative exchange events involved short stretches of DNA on the order of several hundred nucleotide pairs. Although reproduction in E. coli is thought to be largely clonal, clonal reproduction is nevertheless consistent with recombination involving short stretches of DNA because most genes are still transmitted uniparentally. This is yet another example of how a DNA sequence can contain information about its history that cannot easily be inferred from direct experiments.

The process of mutation, which until recently seemed to result from an essentially simple process of nucleotide substitution or rearrangement, is now appreciated to include mechanisms for creating evolutionary novelty through the movement and other activities of transposable elements. Indeed, virtually all proteins may have been created in evolution by the rearrangement of exon units, which code for smaller structural domains able to fold autonomously and carry out elementary functions such as ligand binding. If true, this would mean that the evolution of new functions cannot be likened to the proverbial monkey pecking away at a typewriter in hope of creating something meaningful; the analogy should rather be to a monkey that can shuffle complete words and entire sentences and paragraphs.

Recombination, traditionally viewed as important from the standpoint of creating genetic variation through new combinations of genes, has taken on a new dimension in population genetics because of its conservative role in maintaining similarity between members of multigene families. However, little is known about the rate of gene conversion in multigene families or about the role of intragenic recombination in creating new genetic variation.

The Study of Natural Selection Remains One of the Principal Preoccupations of Evolutionary Biologists

The understanding of the mechanisms of selection in natural populations is still inadequate. At the molecular level, it is necessary to understand how changes in protein molecules affect fitness and to critically evaluate the contribution of selectively neutral mutations to molecular evolution. These problems are ideal for the application of site-directed mutagenesis in experimental organisms such as bacteria, yeast, and Drosophila . At the phenotypic level, it is necessary to understand how genes affecting quantitative characters respond to natural selection. This is an area in which substantial advances in the theory have been made recently and in which further progress can be expected. Analysis of multifactorial traits is essential to understanding the genetic basis and inheritance of many genetically complex disease traits in humans, including the most common birth defects and adult disorders. It is also important in evolution and diversity in interpreting the evolution of such multifactorial traits as morphology.

Significant methodological problems in natural selection include difficulties in measuring reproductive components, including fertility selection and sexual asymmetry in selection, nuclear-cytoplasmic gene interactions in fitness, and the elaboration of statistical models and experimental designs to estimate fitness components when there is inbreeding (as in some plants). Studies of selection in natural habitats are often hampered by lack of a rigorous, quantitative approach to studying the environment and its variation.

Evaluation of the role of population structure in evolution is also marred by important unresolved problems, such as the need to improve methods of estimating migration rate, to define the role of interactions between genotypes in selection, and to evaluate the significance of selection among demes (a local population of closely related organisms) in the genetic divergence and transformation of populations. Genetic differentiation results in variation among populations, and methods for the statistical analysis of such spatial patterning are now being developed.

Progress Is Being Made in Our Understanding of Speciation and the Evolution and Maintenance of Diversity

Organismal diversity is a direct and inevitable outcome of speciation, the process whereby a single species evolves into two or more distinct ones. The conditions required to initiate, promote, and complete the speciation process are still poorly understood and hence controversial. To resolve this problem, a major effort has been made in recent years to examine the biological and genetic attributes of closely related taxa actively undergoing various degrees of differentiation. Three approaches are taken in these investigations: field, experimental, and theoretical.

Significant advances have come from the analysis of the genetic variation and structure in natural populations. Many of these studies are of insects. For example the Hawaiian Drosophila , which have proliferated rapidly on the emerging islands of the archipelago, serve as an outstanding model system for examining the relations among geographic isolation, population size, sexual selection, and genetic divergence. The fact that the islands can be accurately dated in geologic time provides a unique opportunity to ascertain how the species have evolved. Founder events followed by repeated population expansions and contractions accompanied by strong sexual selection appear to have promoted the rapid divergence of isolated populations of these flies.

The causes of speciation are different in Rhagoletis , a group of economically important flies whose larvae infest the fruits of a wide range of plants. Within the past 150 years, species of these flies have formed genetically distinct host races on introduced plants, in the absence of any geographic barriers to gene flow. These races appear to be in the early stages of speciation. Detailed behavioral, ecological, biochemical, and molecular research has revealed that because mating in these flies occurs on the host fruit, genes that govern host choice directly affect mate choice.

Another approach to the study of speciation in natural populations focuses on the genetic and biological outcome of hybridization in zones of overlap either between previously geographically isolated, but closely related, populations that have reestablished contact, or in zones of transition across a sharp ecological boundary between populations adapting to different habitats. These investigations are being carried out on a wide range of animals and plants. The objective of such studies is to establish whether different mate recognition systems and reproductive isolation can evolve in zones of contact as a result of a selective process called reinforcement or develop as a by-product of genomic divergence in isolation. The increased genetic resolution recently provided by molecular techniques is contributing significantly to our understanding of how hybridization affects the speciation process.

A third approach to the study of speciation involves direct laboratory selection experiments. Such experiments suggest that considerable progress toward speciation can occur rapidly, even in the face of considerable gene flow. This experimental approach offers promise for testing some hypotheses of speciation mechanisms now being generated from studies on natural populations.

In recent years, theoretical population genetic models, using analytical and computer stimulation approaches, have been developed in an attempt to understand under what conditions species evolve in nature. These models have become increasingly more sophisticated and biologically meaningful and have yielded insights into the speciation process as well as models for exploring, in nature or in the laboratory, the conditions under which speciation can occur.

The study of speciation, one of the most important fields of research in evolutionary biology, has a direct bearing on our understanding of the origin of organismal diversity in the past, the present, and the future. It has left the descriptive, comparative phase that predominated in the past for a more empirical approach to the study of speciation mechanisms. Sufficient evidence has come from recent studies to indicate that we are on the threshold of resolving some of the most intractable problems concerning modes of speciation. The increasing interest in microbial evolution also encourages a new analysis of the species concept and species formation in prokaryotes.

The Study of Evolution of the Organization and Composition of the Genome Is Still in Its Infancy

Even though we know that the overall genetic organization of the chromosome in certain groups of bacteria is strongly conserved, the reasons are obscure. Similarly, in eukaryotes, no principles are known that govern conservation or changes in chromosome structure or organization. Genomic evolution also includes unknown contributions from various localized and dispersed highly repetitive DNA families and numerous types of transposable elements with different characteristics and evolutionary implications. In a wider sense, genomic evolution also includes that of viral genomes and the interactions with the host genomes. Recently it has become clear that certain plant genomes undergo a novel and potentially major mechanism of evolution in response to environmental stress. For example, plants under stress manifest marked phenotypic changes that are associated with heritable changes in copy number of several multigene families including ribosomal DNA sequences. New methods of manipulating and cloning large DNA molecules will be critical to the study of evolution at the level of the chromosome.

Although ambitious, the synthesis of disciplines that characterize modem evolutionary biology should be extended to embrace areas such as developmental biology, neurobiology, and behavior. Little is known about possible developmental sequences available to organisms with particular genotypes, or about new kinds of developmental pathways that are accessible by mutation from genotypes already existing. In addition, virtually nothing is known about the genetic determination of complex animal behaviors and the manner in which these behaviors feed back on the evolution of molecular and morphological traits.

• The Result Of Evolution

The Study of Adaptation Is Still a Pervasive Theme in Biology

The most dramatic result of the evolutionary process is seen in the adaptations of organisms alive today. One of Darwin's chief accomplishments in The Origin of Species was to show that the exquisite adaptations of organisms that ''so justly excite our admiration" could be explained by the purely mechanistic process of natural selection.

Important research opportunities in studies of adaptation derive from both technical and conceptual innovations during the past several decades. Some of the technical advances have been mentioned. As an example of conceptual innovation, it is now generally agreed that traits do not typically evolve for the good of the group or species as a whole, but for the direct or indirect advantages they confer on their possessor. Interdemic selection may provide an exception to this generalization, but the overall importance of interdemic selection to changing the genotypic composition of a species is unknown. The search for theories other than group selection to explain puzzling traits has led to a rich proliferation of concepts regarding, for example, selection acting not on individuals themselves but through increased fitness of their kin, and the trade-offs between fecundity and mortality in life-history strategies. However, some phenomena remain puzzling, such as that parthenogenesis does not rapidly replace sexual reproduction even though its rate of reproduction is theoretically higher.

Other conceptual advances have also enriched the study of adaptation. One is the realization that organisms often buffer themselves against changes in selection pressures. For example animals can choose species-specific microhabitats, and seeds can germinate in response to cues that signal favorable conditions. Another important concept is that of developmental constraint: the manner in which certain adaptations close off other possible paths of adaptation, thereby constraining the further evolutionary potential of the species. For example, the exoskeleton of arthropods provides attachment sites for muscles enabling rapid movement, but it also limits the maximum size of the animals.

The study of adaptation has also benefited from the integration of previously separated fields. For example, ecology and behavior are becoming increasingly integrated into evolutionary biology. By examining the genetic and phylogenetic aspects of physiological, morphological, and biochemical traits, biologists are forming bridges among evolutionary biology and physiology, development, and molecular biology.

Among numerous promising research opportunities in adaptation are studies of evolutionary and functional morphology, which increasingly includes biomechanics. Application of quantitative engineering principles combined with computer modeling has moved this field from descriptive to analytical studies. The approach enables the analysis of the specific mechanical properties of biological materials, the relation between the design of organisms and their environments, and the understanding of repeatable historical patterns in the evolution of design and the constraints placed on design by evolutionary history.

Physiological adaptations of plants and animals to factors including temperature, aridity, and osmotic stress have been abundantly analyzed by physiological ecologists, whose approach is becoming increasingly evolutionary. Indeed, some workers have begun to examine individual variation in physiological traits find to apportion the variation into genetic and nongenetic causes in attempts to determine physiological mechanisms.

Important Advances Have Been Made in Behavioral Ecology and Evolutionary Biology

The understanding of such phenomena as habitat use, food selection, social aggregation, cooperation, cannibalism, and ritualized conflict has greatly increased in the past decade. Sexual selection has become a major topic in both behavior and population genetics, and the reality of sexual selection by female choice in birds has recently been demonstrated. The next step is to test the prediction that male characteristics evolve in concert with female preference for even more exaggerated male characteristics, virtually without limit. The coevolution of male-female mate recognition characteristics may play a key role in animal speciation.

The evolution of life histories provides an active area of contact between the fields of ecology and evolution, as does the study of how interacting species adapt to each other and how such coevolution affects the structure of ecological communities. During the past decade, such studies have expanded beyond the previous emphases on competition and predation to embrace, among others, parasitism and mutualism.

The study of adaptation has been invigorated by the infusion of new concepts and theories, by an increasingly experimental and analytical approach, and by the increasing communication among fields. The incorporation of population genetic theory and phylogenetic analysis into the study of adaptation has only begun and promises to be instructive. Several hurdles must be overcome to ensure success. Tests of theories in natural populations often require considerable time—often years—before they acquire real substance; in some areas, such as physiology, techniques must be developed to automate the measurement of numerous individuals.

Although modern molecular techniques promise to contribute to an understanding of numerous unresolved questions related to the processes and history of evolution, equally important contributions will emerge from new conceptual, statistical, and technical approaches in areas such as population genetics, phylogenetic analysis, and developmental biology. Foremost among the poorly understood areas in evolution are the relations between evolutionary processes at the population level and the longer term evolutionary changes involved in the origin of species and higher taxa. A bridge between the almost separate domains of population genetics on the one hand and systematics on the other is sorely needed. Progress in building such connections may have to await advances in developmental biology and imaginative new approaches in genetics and development, but some advances in these areas hold out the promise that population and historical studies can inform each other.

For example, we may anticipate that, by the use of molecular sequences or large numbers of morphological traits or both, reasonably reliable phylogenies of groups of related species will soon be abundant. In groups that are amenable to genetic or developmental studies, the conjunction of genetic and phylogenetic or paleontological analysis offers the opportunity for studying numerous open questions. These include issues such as (1) whether rapidly evolving characteristics are more variable genetically than slowly evolving features; (2) whether genetic correlations exist between characteristics that evolve in concert across phylogenies, or whether observed phylogenetic correlations result from co-adaptation and natural selection only; and (3) whether correlations among species result from common ancestry rather than adaptation or genetic correlation. These are some of the rich fields that are available at the organismic level for the exploration of evolution and diversity.

The relation between population genetics and long-term evolution will also be strengthened as evolutionary biologists turn to developmental biology and developmental genetics. The greatest progress will come when the mechanisms of development are more fully understood. Even now we can hope for some understanding, perhaps by developmental comparisons and experiments not only between distantly related kinds of organisms such as frogs and salamanders, but also between closely related species in which hybridization or experimental transfer of genetic material may prove feasible. Among the neglected questions coming to the fore once again are, What is the mechanistic basis of the sterility of species hybrids? Are few genes responsible for hybrid sterility, or many? Why are mutations of large effect generally deleterious and what are their pleiotropic effects? Conversely, what processes are altered when gradual, polygenic changes yield a viable phenotype that may resemble the nonviable phenotype of a single mutation of large effect? What is the developmental nature of invariant or evolutionarily conservative traits, and what is their relation to the concepts of canalized phenotypes that develop in constant ways in a wide range of environments? What relations exist among the functional, phenotypic, genetic, and developmental correlations among traits?

Research in Functional Morphology and Biomechanics Has as a Major Goal the Analysis of Patterns of Diversity at the Level of Whole Organisms

Functional morphologists study mechanisms of integration of organisms, usually within both phylogenetic and evolutionary frameworks. Complex organisms are highly integrated, and the basic pattern of organization of most major taxa is conservative. This conservatism probably arises from couplings, or interlinkages among the parts of organisms that stabilize morphology. These links may be genetic (pleiotropy, genetic correlations, and so forth), developmental (inductive interactions), functional (physiological, behavioral), or structural (direct part-to-part connections). Functional morphologists examine organisms to describe such linkages. Once understood, such couplings can be used to explain why evolution is likely to proceed in certain directions rather than in others and why certain structures and functions have not evolved in the past and are unlikely to appear in the future. Thus, many functional morphologists are concerned with constraints on evolution and on opportunities that arise when such constraints are removed. Furthermore, certain evolutionary phenomena can lead to uncouplings, which may be followed by the incorporation of novelties and adaptive radiation. For example, certain salamanders lost lungs as an adaptation to live in rapidly flowing streams; the hyobranchial system was thereby uncoupled from its role as a respiratory pump and evolved into a high-speed, long-distance projectile tongue. Modem functional morphology uses a large array of methods, including high-speed video, kinematic, and x-ray cine systems for visualizing movement and behavior, electromyographic and other physiological approaches for characterizing patterns of movement, neurobiological methods such as modem staining methods for tracing neural components of integrated systems, and even quantitative genetic methods of analyzing patterns of interaction for analysis of variation within individuals.

Application of principles from the fields of materials science, engineering, cell and developmental biology, ecology, and evolutionary biology to the study of the structure and function of plants and animals has progressed rapidly and holds promise for the future. The field of biomechanics is relatively young; it differs from functional morphology in having a focus on details of structural organization and in having application from the level of cells to that of whole organisms facing the environment. The kinds of studies undertaken range from investigation of the structure of the cytoskeleton to those of the collagenous fiber wrapping of the dermis in whales and fishes and the meaning of these structures for function. Recent discoveries include the biomechanical significance of spicule arrangement in the bodies of sponges, reasons for the organization of the holdfast in giant kelps, and the means by which sea anenomes survive the battering they receive in tidal zones. Biomechanical approaches have led to new understanding of the organization and function of the notochord, of the significance of osteogenic patterns, and of the organization of muscle. Some workers span the small gap to functional morphology, while others extend their interests into surgical and other medical uses of biomechanical perspectives.

Systematics Is a Key Discipline in Evolutionary Biology

In a Chinese proverb, calling things by their proper names—systematics—is the beginning of wisdom. Modern systematics, which is basic to the study of adaptation, stresses the basic recognition and naming role, but simultaneously reaches out to all other disciplines concerned with biological diversity. Systematics comprises taxonomy—that is, surveying, recognizing, naming, describing, and making identifiable the kinds of organisms—and the development of classifications of organisms, placing them into taxa from the population to the kingdom levels. At another level of analysis it embraces the study of the relations, origins, and histories of these taxa, including the factors that led to their origin and shaped their histories.

Systematics, gradually transformed by principles and techniques from other disciplines, has the chief responsibility for analyzing diversity and putting such knowledge into a more accessible form. Cataloguing of organisms is still so incomplete that we do not even know to the nearest order of magnitude the number of species on earth. Although approximately 1.4 million species of all kinds of organisms have been formally named since Linnaeus inaugurated the binomial system of species identification in 1753, this figure grossly underestimates the diversity of life. Considering the prodigious variety of insects alone and the underrepresentation in the catalogue of many types of organisms, such as microbes, it is reasonable to guess that the absolute number of species of all groups on earth falls somewhere between 5 and 30 million.

FUNCTIONAL MORPHOLOGY AND EVOLUTIONARY ECOLOGY

Three of Africa's Great Lakes—Victoria, Tanganyika, and Malawi—are home to three remarkable species assemblages. Each lake contains 150 to 200 endemic species of the family Cichlidae, small to medium-sized sunfishlike fishes. The total of nearly 600 species represents an astonishing 3 percent—perhaps more—of the world's fish species. Why are there so many of them? Does their morphology have anything to do with their remarkable multiplicity of species?

In general, when species coexist, they are partitioning some resource—such as food or space—in such a way as to reduce competitive overlap. Such specialization is often accompanied by diversity of some physical or behavioral features of the species. Studies of the African cichlids reveal enormous diversity in two attributes: their behavior, including feeding, and the morphology of their jaws. Their feeding habits range from scraping algae from the underside of rocks to eating the scales of other fishes. One species frequently bites the eyes out of other fishes, others scrape algae from the leaves of higher plants, some eat whole fish, some eat invertebrates, and so on. Their jaws show remarkable variety in shape, size, and dentition. In addition, cichlids, like most bony fishes, have pharyngeal jaws—"throat teeth." But in cichlids, the pharyngeal jaws are more specialized and variable than in most other bony fishes.

For many years, the Great Lakes cichlids have been regarded as the showcase example of adaptive morphology associated with adaptive radiation. The unusual morphological adaptability of the jaws has been thought to have permitted the remarkable adaptive radiation observed. Certain morphological characteristics of their pharyngeal jaws have allowed those jaws to become adapted to some of the functions usually performed by the mouth jaws. This has freed the mouth jaws to become diversified to perform unique food-gathering functions, almost like a hand; the mouth jaws also have characteristics that seem to allow greater diversification of function than those of most other bony fishes.

The above interpretation is the more plausible because radiation has occurred three separate times in the three lakes. There is even a natural control: Several other families of fishes that lack the cichlids' jaw adaptations inhabit the same lakes but have not radiated similarly.

But recently, puzzling questions have been raised. For example, the cichlid family is represented in the African lakes by two subfamilies, both of which have the specialized pharyngeal and mouth jaws discussed above, specializations presumed to have allowed the great speciation observed. But the explosive speciation has occurred primarily in one subfamily, the Haplochromines. The tilapine subfamily has relatively few species. Why? Another question concerns the characoid fishes of Amazonia, a group of fishes containing the piranhas. They, like the African cichlids, have enormous numbers of species, but they lack the specializations of the cichlids' jaws.

Finally, it has recently become clear that the behavioral and morphological diversity of the African cichlids is strongly influenced by environmental factors. This means that differences observed in nature might not be entirely—or even mostly—genetically based.

The African cichlids remain, as they have long been considered, of enormous evolutionary interest. But, rather than being a textbook example of any one particular phenomenon, they seem to represent a natural laboratory for studying evolution, ecology, and morphology. And that study is still in its exciting early stages.

Proper species classification is important because a species is not like a molecule in a cloud of molecules, but is rather a unique population of organisms; the terminus of a lineage that split off from the most closely related species thousands or even millions of years ago. Species have been shaped into their present forms by mutations and natural selection, during which certain genetic combinations survived and reproduced differentially out of an almost inconceivably larger total. No two species, no matter how closely related, are any more interchangeable than are two Mozart sonatas. Each species of organism is incredibly rich in genetic information. The genetic information in the constituent bases that make up the DNA in a single mouse cell, if translated into ordinary letters of printed text, would nearly fill all 15 editions of the Encyclopedia Britannica published since 1768.

Since other evolutionary disciplines, including ecology, biogeography, and behavioral biology, depend on systematics, an entire hierarchy of important problems must be addressed. Two stand out in the sense that progress toward their solutions is needed to put the other disciplines on a permanently sound basis. The first problem is to define the magnitude and causes of biological diversity, and the second is to determine the most reliable measures of homology and their implications for phylogenetic relationships.

In defining the magnitude and causes of biological diversity, systematics will undoubtedly fall short of obtaining a complete catalog of life on earth, but a determined effort would pay many dividends. A greater understanding of biological diversity promises to resolve some of the conflicts in current theory and at the same time to open productive new areas of research. In addition, the answers will influence a variety of related disciplines, affect our view of the place of humans in the order of things, and open opportunities for the development of new knowledge of social importance. For example, control of mosquito-borne diseases such as malaria has profited from the ability to define as separate species mosquitoes that are morphologically almost identical but that differ in behavior and in their ability to transmit the diseases.

Systematics is also a discipline with a time limit because much diversity is being lost through extinction caused by the accelerating destruction of natural habitats. This is especially true in the tropical moist forests, where more than half of the world's species are thought to exist. Although extinction rates are difficult to estimate, in part owing to inadequate systematics, current rates of extinction seem to approach or exceed 1,000 times the average rate in past geological time. Tragically, and perhaps ominously for human welfare, most of the tropical forests, and with them many thousands of species of plants and animals, seem destined to disappear during the next 30 years. It is not too much to say that humanity is locked into a race in which systematics must play a crucial role.

From a practical standpoint, plants provide many critical medicines and pharmaceuticals, many species contain genes for disease resistance and other desirable traits that can potentially improve agricultural varieties, and many could potentially be developed into important crops themselves. For example, the taxonomy of plants has stimulated and in turn been invigorated by the discovery of more than 10,000 secondary compounds scattered among a vast array of species. These substances (alkaloids, terpenes, phenolics, cyanogens, and glucosinolates) are equally crucial to the understanding of plant evolution and to the improvement of human welfare. Thus, the study of biological diversity and the desire for its preservation are not based on esthetic principles alone.

Systematics Also Includes Studies of the Interrelationships Among Organisms

Studies on phylogenetic relationships among organisms aid in the development and evaluation of theories about evolutionary processes. Models of the origin of species have been stimulated as well as guided by the development of the species concept in systematics. Phylogenetic information is important in many areas of evolutionary biology. For example, in biogeography, the occurrence of flightless ratite birds (ostrich, rhea, emu, and others) in Africa, South America, Australia, and New Zealand is apparently inconsistent with morphological and molecular data indicating that the birds share a common ancestry. The paradox is resolved by the knowledge that the birds all diverged from a common stock that inhabited the great southern continent of Gondwanaland before it split and became dispersed through continental drift. Phylogenetic information is the basis of the comparative method for the study of adaptation. A positive adaptive value for a particular characteristic is suggested when two or more distantly related organisms have undergone parallel evolution in that characteristic, for example flower shape or color. Phylogenetic analysis is also necessary for understanding the sequence in which characteristics have undergone evolutionary transformation and for estimating rates of evolutionary change, be it morphological or molecular.

One of the chief tasks of systematics is the elucidation of phylogenetic, or genealogical, relationships among organisms. Inference of genealogy is a desirable goal both for fossilized forms and for living organisms whose ancestry is poorly documented in the fossil record. The reconstruction of phylogenetic history is often of great interest in itself, for example in determining the ancestral relationships among humans and other higher primates. But the reconstruction of phylogenetic trees has numerous other uses as well. Indeed, phylogenetic data are the source of almost everything we know about the patterns of evolutionary change over the course of millions of years, including convergent evolution, parallel evolution, adaptive radiation, and mosaic evolution. Phylogenetic studies have been essential to understanding how species have arrived at their present geographical distributions and to interpreting processes and rates of change at the level of the DNA.

Only in the past 20 years have the logical and evidential criteria for establishing phylogenetic relationships been articulated. Through these sometimes controversial developments, systematics has become a highly sophisticated, rigorous science in which mathematics, statistics, and molecular biology play leading roles. Modern systematics differs greatly from what it was even 10 years ago and poses extremely complex questions.

An important step in this revolution was the development of methods of classification that allowed treelike diagrams expressing the similarity among organisms to be derived by objective criteria through the use of appropriate mathematical expressions evaluated by computer algorithms. These kinds of clustering procedures first developed for biological classification have since been used in many other applications, for example, in linguistics.

The treelike diagrams derived from clustering procedures do not necessarily reflect the genealogical relationships in phylogenetic trees unless the similarity of two species is directly proportional to how recently they diverged from their common ancestor. Proportionality does not exist when many characteristics undergo convergent evolution or when different evolutionary lineages evolve at different rates. However, methods have also been developed that aim to infer the correct phylogenetic relationships among species, although these methods are sometimes difficult to apply in practice because of uncertainties and ambiguities in the data. An important area of current research is the development of statistical techniques to evaluate the degree of uncertainty in estimates of phylogenetic relationship. Just as estimates of numerical quantities should be accompanied by confidence intervals giving the precision of the estimates, inferred patterns of phylogenetic relationship must be accompanied by some kind of measure of their reliability.

Traditionally relying on the data most readily available, usually the morphological characteristics of preserved museum specimens, modern systematics also includes other sources of data, such as ecology, behavior, genetics, and biochemistry. The power of systematics has recently been augmented by data from molecular biology. Electrophoretically distinguishable proteins are now routinely used to distinguish species and to estimate phylogenetic relationships among closely related species, and restriction enzyme digests of DNA sequences such as mitochondrial DNA provide numerous systematic characters.

• Evolutionary History

The Fossil Record Makes Special Contributions to Evolutionary Biology and to Knowledge of Present-Day Diversity

Although questions of both process and result are central in evolution and diversity, the history of evolution has only one source of primary direct evidence, one court of last resort, which is the fossil record. Studies in paleobiology therefore directly affect all aspects of evolution and diversity.

The fossil record provides the vital time dimension for the understanding of biological diversity and the history of life. The current data base of paleobiology consists of records of some 250,000 extinct species of plants, animals, and microorganisms occurring in deposits spanning more than 3.5 billion years of earth history. Although the record comprises only a small fraction of all the fossil taxa that ever lived, systematic collections in museums and universities contain tens of millions of documented specimens, in many cases with good representation of individual species in space and time.

With respect to the history of diversity, the fossil record can be analyzed to determine whether diversity is higher now than in the geological past, whether the evolution of diversity might be expected to reach a steady-state level, and whether community structure has changed over geological time.

Paleobiology is unique in being the only source of data about certain evolutionary processes and events. For example, although the observational and experimental work of most biologists is necessarily limited to processes and phenomena that are relatively rapid or common, paleobiologists capitalizing on the depth of the geological record have access to much rarer events.

The geological record also documents a unique and lengthy natural experiment in adaptation. Many biological innovations originated, flourished, and died out long before the modem biota emerged. Studies in paleobiology can shed light on when these lost adaptations originated and whether they were better solutions to functional problems than are found among living organisms today.

Adaptive radiations—bursts of speciation in which the number of species in a biological group or adaptive zone increases exponentially during a relatively short time, with accompanying expansion in the diversity of structure and function—is well documented in the fossil record, but it is not clear whether these grand adaptive radiations are analogous to the smaller-scale bursts of speciation observed, for example, among Hawaiian drosophilids and African cichlid fish.

THE RISE OF THE ANTS

In 1967, Harvard University received the first known specimens of fossil ants of Mesozoic age, two beautifully preserved specimens in the clear orange amber from a redwood tree that grew 80 million years ago in New Jersey. These specimens were something of a breakthrough in the study of insect evolution. Until then the oldest known fossils were about 30 to 40 million years old (from the Oligocene epoch) and quite modern in aspect. The main features of ant evolution had already been fleshed out. The only phylogenetic tree that could be drawn from such evidence was the canopy, with the trunk and roots cut off. The Mesozoic ants provided what appeared to be a piece of the trunk.

Soon afterward, Soviet paleontologists began to describe a long series of other antlike fossils, also about 80 million years old, giving a separate scientific name to almost every specimen. When all these bits and pieces were fitted together and the New Jersey fossils added in 1986, a remarkable picture emerged: The specimens fell into three classes, representing the worker caste, the queen caste, and the male of the most primitive ants. The workers lacked wings and had proportionately small abdomens, the hallmarks of a sterile caste. These fossils made it possible to conclude that social life had been established in the ants by 80 million years ago, a startling conclusion in view of the earlier lack of such ancient fossils.

A close examination of the American and Soviet fossils showed them to be similar to what had been expected for ancestral ants. Their anatomy was a mosaic of traits, some typical of nonsocial wasps and some more modern—but still typical of generalized ants. They provided the first clue concerning the group of wasps from which ants arose.

The Harvard collection recently obtained the first ant fossils of mid-Eocene age, from Arkansas this time. Chinese and Soviet paleontologists were close behind, discovering Eocene specimens from Manchuria and Sakhalin, respectively. These ants are thought to be 50 to 60 million years old, and most of them are very different from the Mesozoic fossils. They are diverse, representing both modern taxonomic groups and (in one case) a stock not too distant from the Mesozoic ants. It thus seems that the ants, like the mammals, crossed a threshold around the end of the Mesozoic era. For some reason not yet understood, they expanded into a richly various, world-dominant group.

Entomologists and paleontologists continue to search avidly for fossils from Mesozoic and early Cenozoic deposits. The questions we hope to answer include when, where, and from which wasplike insects the ants arose; exactly when they radiated into their modern aspect; the directions they took when spreading around the world; and, not least, what traits contributed to their spectacular success.

Extinction Has Been the Fate of Almost All Species That Have Ever Lived

Extinction, as a biological process, is difficult to study in modern environments. Although the background rate of extinction is low—estimated as about one global extinction per million species per year—extinction is not only frequent on a geological time scale but has been responsible for many complete turnovers in the biological composition of the earth. A proper understanding of the evolutionary process is impossible without knowledge of rates of extinction, quite apart from the importance of such knowledge in evaluating the magnitude of the increase in rates of extinction resulting from human activities in modern times.

Understanding the environmental causes and evolutionary implications of the occasional, brief periods of mass extinction in earth history is a key problem in paleobiology. The most severe mass extinction occurred 250 million years ago and eliminated between 75 and 95 percent of the species then alive. In short, the global biota had a close call with total annihilation. Somewhat less severe mass extinctions are scattered throughout the fossil record. Recent work on the likelihood that some mass extinctions were caused by meteorite impact shows promise of establishing strong connections between biological evolution and the cosmic environment. When combined with the more speculative possibility that impact-induced extinctions are regularly periodic, this hypothesis opens the possibility for major shifts in the way the evolution of the global biota is interpreted.

Within the past 2 million years of the fossil record, constituting the Pleistocene epoch, are special opportunities for studies of biological diversity. During this period, the biota was essentially modem but subjected to the effects of well-documented major changes in climate and geography that set the stage for the present distribution of plant and animal species. Modern tropical rain forests, to pick just one example, can be understood only by knowing the historical underpinnings that led to their present distribution and composition. This understanding is critical in developing a strategy for dealing with the effects of human activities, especially in the moist tropics.

Palcobiologists Have Made Major Progress in the Past Two Decades

Research results have been astounding, at the other end of the time scale, in deciphering the oldest records of life on earth. Not only did life begin far earlier than biologists had previously envisaged, but, perhaps even more surprising, the earth's biota was composed solely of bacteria over such an extended period. These fossil discoveries have recast concepts of evolution and diversity and have reemphasized the fact that, when viewed over the long sweep of geological time, a significant part of evolutionary progress has resulted from changes in the intracellular biochemistry of bacteria.

Paleobiology includes several research areas that have special promise of making significant contributions to evolutionary biology and to other fields of the natural sciences. Among these are the origin of life itself, including not only when life began, by what processes and in what types of environments, but also whether life might exist elsewhere in our solar system or in the universe. Such issues are ripe for exploration during the coming decade because recent progress in studies of ancient Precambrian fossils has extended the known record of life on earth to more than 3.5 billion years. Studies of even more ancient deposits, coupled with laboratory studies of chemical reactions that can occur in a lifeless environment and biochemical studies of existing microbial organisms, promise to provide new evidence of the beginnings of life and of the environment in which life originated.

Organisms Alive Today Are Well Adapted to the Vagaries of Their Present-Day Environment

Environmental conditions such as atmospheric composition, day-night light regime, and temperature conditions have changed markedly over the course of geological time. Until about 1.7 billion years ago, well after the origin of living systems, the atmosphere contained too little oxygen to sustain obligately air-breathing forms of life. Day length has progressively lengthened as the distance between the earth and moon has gradually increased, and there is good evidence that the earth's average surface temperature has changed markedly. Each evolving species became adapted to the environment in which it originated, and as the environment changed, life evolved and built on foundations that had become established under earlier regimes. Therefore, recorded in the genetics, biochemistry, cellular structure, and gross anatomy of living organisms may be a coded history of their evolution. For example, analyses of growth bands in fossil corals and mollusks have made it possible to track the changes in day length caused by tidal friction. Even more spectacular has been the recent recognition of Milankovich cycles of climatic change over the past 700,000 years, which almost certainly were responsible for the pulses of continental glaciation during the Pleistocene epoch.

Deep-sea drilling during the past two decades has provided continuous sections in which important population-level analyses of evolutionary changes are feasible. This increased resolution in the fossil record introduces a time scale comparable to that of microevolutionary change in population genetics, and it opens a more complete synthesis of these two disciplines. The oceanic fossil record is excellent for the last 160 million years, and the deep-sea cores provide a rich source of information on the evolution of single-species lineages. Statistical analyses have already documented important patterns of morphological change and the not-uncommon lack of such change known as stasis. But the surface of this field has only been scratched by the investigations carried out thus far, and we have much more to learn about the tempo and mode of evolution.

Much also remains to be learned regarding the timing and nature of major evolutionary events. Some of them, such as the origin of invertebrates, vertebrates, flowering plants, angiosperms, and humans, have been recognized as important research problems since the mid-nineteenth century. Other events, such as the advent of photosynthesis, oxygen-dependent respiration, the anaerobic-aerobic global ecosystem, nucleated cells, and eukaryotic sexual reproduction, have been addressed only recently with the upsurge of interest in the Precambrian fossil record. Future studies will promote a better understanding of the timing and context of major evolutionary events in the history of life on earth.

• Current Status Of Research

Contemporary Research in Evolution and Diversity Features Several Exciting Growing Points

A particularly promising field spanning the synthesis of molecular biology and evolutionary biology is expected to reveal new evolutionary principles even as it resolves some longstanding issues. Important as this new synthesis is, it must be emphasized that not everything in evolution and diversity can be reduced to molecular biology.

Many central issues of evolution at the organismic level require different kinds of approaches. These include the study of the evolution of complex multifactorial traits within populations and the evolutionary role of selection among populations. Innovative approaches to uniting physiology, behavior, and development should also be encouraged.

Those who set research priorities in evolution and diversity must also recognize the continuing importance of cataloguing the diversity of life on earth and understanding its origins through speciation and its disappearance through extinction. Apart from the scientific value of such research are the many potential practical applications of the findings in medicine, agriculture, and biotechnology. Groups of organisms that are already relatively well known, such as vertebrates, plants, and butterflies, are important to study because of the light further information about them would shed on overall biogeographic problems. In addition, economically important groups of organisms, such as legumes and mosquitoes, should be emphasized in choosing priorities for study. Areas of vegetation that are already decimated and those that are being destroyed rapidly but that contain large numbers of endemic species should also receive special emphasis. Concerted efforts to survey more or less completely the biota of selected places, especially in the disappearing forests of the tropics, would be much more rewarding than miscellaneous sampling of poorly known groups over wide areas. Greater attention should also be given to groups that are especially tractable for the solution of basic problems in ecology, population biology, and evolution. To accomplish this, additional systematic biologists must be trained and employed, since the current world supply is much too limited to attack the millions of species of unknown or poorly known organisms profitably.

Paleobiology also presents significant new opportunities for breakthroughs in understanding the history of life on earth, including its earliest history in the Precambrian, its diversification and geographical distribution, and its extinction through, in some cases, global processes.

Collections and Special Facilities

Museums are one logical place to concentrate the effort to encompass diversity.

These institutions are already the repositories of vast numbers of priceless specimens, often representing species that are endangered or recently extinct. Yet most of the collections are fallow, and the halls of some of the leading research museums are largely empty of qualified researchers. The same is true of zoos and botanical gardens, which are in effect museums filled with living specimens. One of the premier tropical botanical gardens in the continental United States has purchased no major items of research equipment in 20 years. Although it averages only one postdoctoral fellow per year, it could easily accommodate six.

An additional need exists for regional or international centers for the storage and analysis of fossil pollen and other microfossils, which are vital in the reconstruction of evolutionary histories and past environmental change. For example, we are only now becoming aware of the considerable extinction of species that has been caused by human disturbances, especially on islands, lakes, and other geographically restricted habitats. One of the most promising domains of research is the detailed analysis of this impoverishment during the past several thousand years, with an emphasis on the factors that make certain species more vulnerable than others.

The future of systematics and its contribution to evolutionary studies depend on collaboration among workers in different fields, funding of interdisciplinary studies, and mutual education. Museums, the traditional home of systematics, will find it necessary to expand their facilities and personnel to encompass statistical, molecular, and experimental approaches. The traditionally modest sums granted to systematists will not support molecular investigations, and it will be useful to set up facilities for molecular systematics that can be used by multiple workers. Above all, university biology departments, in their staffing and curricular decisions, must take into account the growing impact of the new systematics on the study of evolution and its implications throughout biology, from molecular biology to ecology.

Museums are also vital to the continued health of research on the fossil record by maintaining and developing systematic collections. These Collections are the lifeblood of research progress. Research questions change continually, and it is important that museum collections remain an effective source of empirical data and that the data be actively studied and described by competent specialists.

The paleontological collections of the United States are in reasonably good shape, thanks to many years of financial support from the Biological Research Resources program of the National Science Foundation. Continued support is critical to sustain active research programs of relevance to broader problems of evolutionary biology. Museum collections are becoming especially critical in some areas because of the phasing out of support for collections by many major research universities.

Collection and Conservation of Germplasm Is Crucial For Improved Agricultural Production

Human activities associated with modern civilizations are causing a loss of diversity at all levels of biological organization. Once lost, this store of genetic diversity can never be recovered. A case in point is the loss of genetic diversity associated with the primitive land races (plants that are adapted to a region in which they evolved) and wild relatives of our crop plants. These genetic resources have repeatedly provided genes for disease resistance when agriculture has been challenged by serious disease epidemics, and these resources constitute an important source of novel phenotypes in conventional plant improvement. They must be found and conserved for our common good.

Modem agriculture is characterized by extensive plantings of genetically uniform monocultures. For example, genetically uniform hybrid corn is widely grown in the United States. Genetically uniform populations have the advantages of high yields, uniform size, and uniform dates of maturity, and these features have played a major role in the great increase in productivity of agriculture in the United States during the past 50 years. Uniformity of size and maturity are also required by highly mechanized agricultural practices.

On the downside, genetically uniform crops are vulnerable to large losses from pest or disease outbreaks because monocultures may lack the genetic variability for resistance to the pathogens. In 1970, a fungal pathogen raced through the U.S. corn crop in the corn leaf-blight epidemic. It was quickly discovered that susceptibility to the fungal pathogen was associated with a particular mitochondrial genotype that had been widely incorporated into breeding stocks. Luckily, other mitochondrial genotypes conferred resistance, and the resistant genotypes were introduced into commercial lines of corn. By 1971 corn varieties resistant to the leaf blight had largely replaced the susceptible type in agricultural production, and the corn crop was protected. The resistant types were available because an international effort had been made to conserve plant genetic resources for just such contingencies.

A second major disadvantage associated with the wide, and in some cases nearly global, adoption of monocultures is that these plantings supplant and drive to extinction the wild relatives and primitive cultivated forms of crop plants, which provide a source of genetic variants for future breeding efforts. Genetic conservation is faced with two problems—how to save and maintain useful plant germplasm and how to evaluate plant gene pools in order to preserve as wide a sample of potentially useful genetic variants as possible. The problem of evaluation is particularly difficult because we have no way of predicting which kinds of novel genetic variants the future may require. At present, the best that can be done is to evaluate the plants of interest for a wide range of genetic traits and select a sample for conservation that includes as much diversity as possible. Little is known about the adequacy and scope of contemporary germplasm collections. Genetic screening procedures and statistical sampling plans need to be developed for this task.

Finally, what little effort is expended to protect plants is almost entirely devoted to crop plants and their wild relatives—about 150 species out of the more than 260,000 kinds of plants known. Botanists estimate that tens of thousands of kinds of plants could probably be developed into useful crops-not only for food but also as sources of medicines, oils, waxes, and other chemicals of industrial importance-if we would carry out the appropriate investigations, identify them, and develop them according to their cultural requirements. Virtually no effort is being expended in such investigations; yet fully a quarter of all plant species, along with a similar proportion of animals and microorganisms, are in danger of extinction. Even if the techniques of genetic engineering are fully applied to the development of new kinds of crops, there will need to be a source of appropriate genes; the plants that we are passively allowing to become extinct could well provide such genes, and we should find and conserve them while they still exist.

• Cite this Page National Research Council (US) Committee on Research Opportunities in Biology. Opportunities in Biology. Washington (DC): National Academies Press (US); 1989. 8, Evolution and Diversity.
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The Diversity of Life

The fact that biology, as a science, has such a broad scope has to do with the tremendous diversity of life on earth. The source of this diversity is evolution, the process of gradual change during which new species arise from older species. Evolutionary biologists study the evolution of living things in everything from the microscopic world to ecosystems.

The evolution of various life forms on Earth can be summarized in a phylogenetic tree (Figure 1). A phylogenetic tree is a diagram showing the evolutionary relationships among biological species based on similarities and differences in genetic or physical traits or both. A phylogenetic tree is composed of branches (the lines) and nodes (places where two lines diverge). The internal nodes represent ancestors and are points in evolution when, based on scientific evidence, an ancestor is thought to have diverged to form two new species. The length of each branch is proportional to the time elapsed since the split.

While this is the most common way that is used to group organisms, other divisions have been proposed.

• Some scientists believe that organisms should be divided into two groups: Prokaryota (or Monera) and Eukaryota. In this method, Archae is typically included in Prokaryota. This view has become less popular due to scientific advancements, specifically genetic analysis of various organisms.
• Another two-group division groups Archae with Eukaryotes. This is often called the “Eocyte hypothesis”. This hypothesis has become more popular as the genomes of more Archaeic organisms are sequenced.

None of the three systems currently include non-cellular life. As of 2011 there is talk about Nucleocytoplasmic large DNA viruses possibly being a fourth branch domain of life, a view supported by researchers in 2012.

Stefan Luketa in 2012 proposed a five-domain system, adding Prionobiota (acellular and without nucleic acid) and Virusobiota (acellular but with nucleic acid) to the traditional three domains.

Evolution Connection

Carl woese and the phylogenetic tree.

In the past, biologists grouped living organisms into five kingdoms: animals, plants, fungi, protists, and bacteria. The organizational scheme was based mainly on physical features, as opposed to physiology, biochemistry, or molecular biology, all of which are used by modern systematics. The pioneering work of American microbiologist Carl Woese in the early 1970s has shown, however, that life on Earth has evolved along three lineages, now called domains—Bacteria, Archaea, and Eukarya. The first two are prokaryotic cells with microbes that lack membrane-enclosed nuclei and organelles. The third domain contains the eukaryotes and includes unicellular microorganisms together with the four original kingdoms (excluding bacteria). Woese defined Archaea as a new domain, and this resulted in a new taxonomic tree (Figure 1). Many organisms belonging to the Archaea domain live under extreme conditions and are called extremophiles. To construct his tree, Woese used genetic relationships rather than similarities based on morphology (shape).

Woese’s tree was constructed from comparative sequencing of the genes that are universally distributed, present in every organism, and conserved (meaning that these genes have remained essentially unchanged throughout evolution). Woese’s approach was revolutionary because comparisons of physical features are insufficient to differentiate between the prokaryotes that appear fairly similar in spite of their tremendous biochemical diversity and genetic variability (Figure 3). The comparison of homologous DNA and RNA sequences provided Woese with a sensitive device that revealed the extensive variability of prokaryotes, and which justified the separation of the prokaryotes into two domains: bacteria and archaea.

Unless otherwise noted, images on this page are licensed under CC-BY 4.0  by  OpenStax .

Text adapted from:

OpenStax , Concepts of Biology. OpenStax CNX. May 25, 2017 https://cnx.org/contents/[email protected]:gNLp76vu@13/Themes-and-Concepts-of-Biology

Eocyte Hypothesis, Wikipedia.  May 25, 2017. https://en.wikipedia.org/wiki/Eocyte_hypothesis

Domain (biology), Wikipedia. May 25, 2017. https://en.wikipedia.org/wiki/Domain_(biology)

Principles of Biology Copyright © 2017 by Lisa Bartee, Walter Shriner, and Catherine Creech is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Diversity in Living Organisms

If you simply have a look, you will see a bewildering variety of living things around you. From the potted plant on your desk to the bird on your window to the microscopic germs on your hand, the diversity in living organisms is truly mind-blowing! Let us explore this diversity and also take a look at how living organisms are classified.

• Classification and its Types
• Five Kingdom Classification
• Plant Kingdom
• Animal Kingdom
• Nomenclature

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NCERT Exemplar Class 9 Science Solutions for Chapter 7 - Diversity In Living Organisms

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Multiple choice questions.

1. Find out incorrect sentence

(a) Protista includes unicellular eukaryotic organisms

(b) Whittaker considered cell structure, mode and source of nutrition for classifying the organisms into five kingdoms

(c) Both Monera and Protista may be autotrophic and heterotrophic

(d) Monerans have a well-defined nucleus

Answer is (d) Monerans have a well-defined nucleus

Explanation:

Monerans include single-celled prokaryotes, actinomycetes and photosynthetic blue-green algae. Monerans don’t have well-defined nuclei and cell organelles.

2. Which among the following has specialised tissue for the conduction of water?

(i) Thallophyta

(ii) Bryophyta

(iii) Pteridophyta

(iv) Gymnosperms

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (iii) and (iv)

(d) (i) and (iv)

Answer is (c) (iii) and (iv)

Thallophytes and Bryophytes don’t have specialized tissues for water conduction, whereas Pteridophytes and Gymnosperms have specialized tissues for the conduction of water.

3. Which among the following produces seeds?

(a) Thallophyta

(b) Bryophyta

(c) Pteridophyta

(d) Gymnosperms

Answer is (d) Gymnosperms

Gymnosperms are flowerless plants that produce seeds. But the seeds are not covered within an ovary and are hence called “naked seeds”.

4. Which one is a true fish?

(a) Jellyfish

(b) Starfish

(c) Dogfish

(d) Silverfish

Answer is (c) Dogfish

Jellyfish is a coelenterate, starfish belongs to Echinodermata, and silverfish is an Arthropod.

5. Which among the following is exclusively marine?

(a) Porifera

(b) Echinodermata

(c) Mollusca

Answer is (b) Echinodermata

Echinodermata is exclusively found in the marine environment, whereas Porifera, Molluscs and Pisces can be found in both marine and freshwater.

6. Which among the following has an open circulatory system?

(i) Arthropoda

(ii) Mollusca

(iii) Annelida

(iv) Coelenterata

(b) (iii) and (iv)

(c) (i) and (iii)

(d) (ii) and (iv)

Answer is (a) (i) and (ii)

Annelida and Coelenterata have a closed circulatory system, whereas Arthropods and Mollusca have an open circulatory system.

7. In which group of animals is the coelom filled with blood?

(a) Arthropoda

(b) Annelida

(c) Nematoda

(d) Echinodermata

Answer is (a) Arthropoda

Annelida, Nematoda and Echinodermata don’t have blood, and Arthropods’ coelom is filled with blood.

8. Elephantiasis is caused by

(a) Wuchereria

(b) Pinworm

(c) Planarians

(d) Liver flukes

Answer is (a) Wuchereria

Wuchereria is a human parasite which causes Elephantiasis. Elephantiasis is spread through mosquitos.

Pinworm is a common intestinal parasite and causes enterobiasis

Planarians are non-parasitic flatworms

Liver flukes are flatworms that cause liver rot in Humans.

9. Which one is the most striking or (common) character of the vertebrates?

(a) Presence of notochord

(b) Presence of triploblastic condition

(c) Presence of gill pouches

(d) Presence of coelom

Answer is (a) Presence of notochord

The presence of triploblastic condition, presence of gill pouches, and presence of coelom are found in both vertebrates and invertebrates, but Notochord is exclusively present in invertebrates.

10. Which among the following have scales?

(i) Amphibians

(ii) Pisces

(iii) Reptiles

(iv) Mammals

(a) (i) and (iii)

(c) (ii) and (iii)

(d) (i) and (ii)

Answer is (c) (ii) and (iii)

Amphibians and mammals don’t have scales on their body, whereas Pisces and reptiles have scales on their body.

11. Find out the false statement

(a) Aves are warm-blooded, egg laying and have a four-chambered heart

(b) Aves have a feather-covered body, forelimbs are modified into wings and breathe through the lungs

(c) Most mammals are viviparous

(d) Fishes, amphibians and reptiles are oviparous

Answer is (d) Fishes, amphibians and reptiles are oviparous

Some fishes are viviparous, but Amphibians show external fertilization they can neither be kept under oviparous nor be viviparous hence statement (d) is wrong.

12. Pteridophyta do not have

(c) flowers

Answer is (c) flowers

13. Identify a member of Porifera

(a) Spongilla

(b) Euglena

(c) Penicillium

Answer is (a) Spongilla

Euglena is a protozoan.

Penicillium is a fungus

Hydra is a Coelenterata

14. Which is not an aquatic animal?

(b) Jellyfish

(d) Filaria

Answer is (d) Filaria

Filaria is a disease caused by Wuchereria. It is spread by Mosquitos.

15. Amphibians do not have the following

(a) Three-chambered heart

(b) Gills or lungs

(d) Mucus glands

Answer is (c) Scales

Amphibians have 3 chambered hearts. Lungs are present in Adults, and Gills are present in tadpoles. Mucous glands are present on the skin of Amphibians.

16. Organisms without nucleus and cell organelles belong to

(ii) protista

(iii) cyanobacteria

(iv) archaebacteria

(c) (i) and (iv)

(d) (ii) and (iii)

Answer is (b) (iii) and (iv)

Cyanobacteria and archaebacteria are prokaryotes, and they do not have well-defined nuclei and cell organelles.

Fungi and Protista are Eukaryotes which possess Cell organelles and nuclei.

17. Which of the following is not a criterion for the classification of living organisms?

(a) Body design of the organism

(b) Ability to produce one’s own food

(c) Membrane-bound nucleus and cell organelles

(d) Height of the plant

Answer is (d) Height of the plant

The height of a plant is an attribute which is related to bushes and trees, which are part of Kingdom Plantae hence the height of the trees cannot be a criterion for the classification of living organisms.

18. The feature that is not a characteristic of protochordata  

(b) Bilateral symmetry and coelom

(c) Jointed legs

(d) Presence of circulatory system

Joined legs are a characteristic feature of Arthropods hence the answer is C)

Protochordata is triploblastic with a bilaterally symmetric body and coelom. They show notochord at some stage of life, and they are marine living.

19. The locomotory organs of Echinodermata are

(a) tube feet

(b) muscular feet

(c) jointed legs

(d) parapodia

Answer is (a) tube feet

Tube feet in Echinodermata help in locomotion and respiration

20. Corals are

(a) Poriferans attached to some solid support

(b) Cnidarians, which are solitary living

(c) Poriferans present at the sea bed

(d) Cnidarians that live in colonies

Answer is (d) Cnidarians that live in colonies

21. Who introduced the system of scientific nomenclature of organisms

(a) Robert Whittaker

(b) Carolus Linnaeus

(c) Robert Hooke

(d) Ernst Haeckel

Answer is (b) Carolus Linnaeus

Carolus Linnaeus introduced binomial nomenclature, which is a simplified method of naming organisms. Binomial nomenclature gives each organism a scientific name that has two parts. The first part is a Genus, and the second part is Species.

22. Two-chambered heart occurs in

(a) crocodiles

(d) amphibians

Answer is (b) fish

Amphibians have 3 chambered hearts. Aves and crocodiles have 4 chambered hearts.

23. Skeleton is made entirely of cartilage in

(d) None of these

Answer is (a) Sharks

Sharks are cartilaginous fish, whereas Tuna and Rohu are bony fishes.

24. One of the following is not an Annelid

(b) Earthworm

(d) Urchins

Answer is (d) Urchins

Urchins are Coelenterates

25. The book Systema Naturae was written by

(a) Linnaeus

(b) Haeckel

(c) Whittaker

(d) Robert Brown

Answer is (a) Linnaeus

26. Karl Von Linne was involved with which branch of science?

(a) Morphology

(b) Taxonomy

(c) Physiology

(d) Medicine

Answer is (b) Taxonomy

27. Real organs are absent in

(a) Mollusca

(b) Coelenterata

(c) Arthropoda

Answer is (b) Coelenterata

Coelenterates have tissue-level organization hence they lack real organs.

28. Hard calcium carbonate structures are used as skeletons by

(a) Echinodermata

(b) Protochordata

(d) Nematoda

• Echinodermata

Echinodermata is spiny skinned organisms which are exclusively free-living marine animals. They are triploblastic and have a coelomic cavity. They use a unique water-driven tube from moving, and they contain calcium carbonate structures which are used as a skeleton.

29. Differentiation in segmental fashion occurs in

(d) Ascaris

Answer is (a) Leech

Leech belongs to Annelids, and it shows metameric body segmentation.

30. In a taxonomic hierarchy, family comes between

(a) Class and Order

(b) Order and Genus

(c) Genus and Species

(d) Division and Class

Answer is (b) Order and Genus

Taxonomic hierarchy

31. 5-Kingdom classification is given by

(b) R. Whittaker

(c) Linnaeus

(d) Haeckel

Answer is (b) R. Whittaker

R. Whittaker proposed 5 kingdom classification, which includes Monera, Protista, Fungi, Plantae and Animalia.

32. Well-defined nucleus is absent in

(a) blue green algae

(b) diatoms

Answer is (a) blue-green algae

Blue-green algae belong to prokaryotes which do not have a well-defined nucleus and cell organelles.

33. The ‘Origin of Species’ is written by

(d) Whittaker

Answer is (b) Darwin

34. Meena and Hari observed an animal in their garden. Hari called it an insect, while Meena said it was an earthworm. Choose the character from the following, which confirms that it is an insect.

(a) Bilateral symmetrical body

(b) Body with jointed legs

(c) Cylindrical body

(d) Body with little segmentation

Answer is (b) Body with jointed legs

Body with jointed legs is a characteristic feature of the Kingdom Arthropoda, and all the insects belong to this kingdom.

Short Answer Questions

35. Write true (T) or false (F)

(a) Whittaker proposed five kingdom classifications.

(b) Monera is divided into Archaebacteria and Eubacteria.

(c) Starting from Class, Species comes before the Genus.

(d) Anabaena belongs to the kingdom Monera.

(e) Blue-green algae belong to the kingdom Protista.

(f) All prokaryotes are classified under Monera.

c) Taxonomic hierarchy

e) Blue-green algae belonged to Kingdom Monera

36. Fill in the blanks

(a) Fungi show———mode of nutrition.

(b) Cell wall of fungi is made up of ———.

(c) Association between blue-green algae and fungi is called as———.

(d) Chemical nature of chitin is ———.

(e) ———has the smallest number of organisms with the maximum number of similar characters

(f) Plants without well-differentiated stems, roots and leaves are kept in ———.

(g) ———are called as amphibians of the plant kingdom

• Fungi show a Saprophytic mode of nutrition.
• The cell wall of fungi is made up of Chitin.
• The association between blue-green algae and fungi is called Lichens.
• The chemical nature of chitin is Carbohydrate.
• Species have the smallest number of organisms with a maximum number of similar characters.
• Plants without well-differentiated stems, roots and leaves are kept in Thallophyta.
• Bryophytes are called amphibians of the plant kingdom.

37. You are provided with the seeds of the gram, wheat, rice, pumpkin, maize and pea. Classify whether they are monocots or dicots.

Wheat-Monocot

Rice- Monocot

Pumpkin- Dicot

Maize- Monocot

38. Match items of column (A) with items of column (B)

(A) – (B)

(a) Naked seed – (A) Angiosperms

(b) Covered seed – (B) Gymnosperms

(c) Flagella – (C) Bryophytes

(d) Marchantia – (D) Euglena

(e) Marsilea – (E) Thallophyta

(f) Cladophora – (F) Pteridophyta

(g) Penicillium – (G) Fungi

(a) Naked seed -(B) Gymnosperms

(b) Covered seed -(A) Angiosperms

(c) Flagella -(D) Euglena

(d) Marchantia -(C) Bryophytes

(e) Marsilea -(F) Pteridophyta

(f) Cladophora -(E) Thallophyta

(g) Penicillium -(G) Fungi

39. Match items of column (A) with items of column (B)

(a) Pore-bearing animals – (A) Arthropoda

(b) Diploblastic – (B) Coelenterata

(c) Metameric segmentation – (C) Porifera

(d) Jointed legs – (D) Echinodermata

(e) Soft-bodied animals – (E) Mollusca

(f) Spiny-skinned animals – (F) Annelida

(a) Pore-bearing animals – (C) Porifera

(c) Metameric segmentation – (F) Annelida

(d) Jointed legs – (A) Arthropoda

(f) Spiny-skinned animals – (D) Echinodermata

40. Classify the following organisms based on the absence/presence of true coelom (i.e., acoelomate, pseudocoelomate and coelomate)

Spongilla, Sea anemone, Planaria, Liver fluke

Wuchereria, Ascaris, Nereis, Earthworm,

Scorpion, Birds, Fishes, Horse

Spongilla- acoelomate

Sea anemone- acoelomate

Planaria- acoelomate

Liver fluke- acoelomate

Wuchereria-pseudocoelomate

Ascaris-pseudocoelomate

Nereis- coelomate

Earthworm- coelomate

Scorpion- coelomate

Birds- coelomate

Fishes- coelomate

Horse- coelomate

41. Endoskeleton of fishes is made up of cartilage and bone; classify the following fishes as cartilaginous or bony

Torpedo, Sting ray, Dogfish,

Rohu, Angler fish, Exocoetus

Torpedo- cartilaginous

Stingray- cartilaginous

Dogfish- cartilaginous

Angler fish- bony

Exocoetus- bony

42. Classify the following based on the number of chambers in their heart. Rohu, Scoliodon, Frog, Salamander, Flying lizard, King Cobra, Crocodile, Ostrich, Pigeon, Bat, Whale.

Rohu- 2 chambered

Scoliodon-2 chambered

Frog-3 chambered

Salamander-3 chambered

Flying lizard-3 chambered

King Cobra-3 chambered

Crocodile-4 chambered

Ostrich-4chambered

Bat-4chambered

Whale-4 chambered

43. Classify Rohu, Scolidon, Flying lizard, King Cobra, Frog, Salamander, Ostrich, Pigeon, Bat, Crocodile and Whale into the cold-blooded/warm-blooded animals.

Rohu- Cold Blooded

Scolidon- Cold Blooded

Flying lizard- Cold Blooded

King Cobra- Cold Blooded

Frog- Cold Blooded

Salamander- Cold Blooded

Ostrich- Warm Blooded

Pigeon- Warm Blooded

Bat- Warm Blooded

Crocodile- Cold Blooded

Whale- Warm Blooded

44. Name two egg-laying mammals.

Billed platypus and the echidna are two egg-laying mammals

45. Fill in the blanks

(a) Five kingdom classification of living organisms is given by ———.

(b) Basic smallest unit of classification is ———.

(c) Prokaryotes are grouped in Kingdom ———.

(d) Paramecium is a protista because of its ———.

(e) Fungi do not contain ———.

(f) A fungus ——— can be seen without a microscope.

(g) Common fungi used in preparing the bread is ———.

(h) Algae and fungi form a symbiotic association called ———.

(a) Five kingdom classification of living organisms is given by Robert Whittaker .

(b) The basic smallest unit of classification is Species .

(c) Prokaryotes are grouped in Kingdom Monera .

(d) Paramecium is a protista because of its Eukaryotic unicellular morphology .

(e) Fungi do not contain Chlorophyll .

(f) A fungus Mushroom can be seen without a microscope.

(g) Common fungi used in preparing bread is Yeast .

(h) Algae and fungi form symbiotic associations called Lichens .

46. Give True (T) and False (F)

(a) Gymnosperms differ from Angiosperms in having covered seed.

(b) Non-flowering plants are called Cryptogamae.

(c) Bryophytes have conducting tissue.

(d) Funaria is a moss.

(e) Compound leaves are found in many ferns.

(f) Seeds contain an embryo.

47. Give examples for the following

(a) Bilateral, dorsiventral symmetry is found in———.

(b) Worms causing disease elephantiasis is———.

(c) Open circulatory system is found in———where the coelomic cavity is filled with blood.

(d) ———are known to have pseudocoelom.

(a) Bilateral, dorsiventral symmetry is found in Liver Fluke.

(b) Worms causing the disease elephantiasis is Filarial worm.

(c) Open circulatory system is found in Arthropods where the coelomic cavity is filled with blood.

(d) Nematodes are known to have pseudocoelom.

48. Label a,b,c and d. given in Fig. 7.1 Give the function of (b)

• Pectoral fin

49. Fill in the boxes given in Fig. 7.2 with appropriate characteristics/plant group (s)

• Thallophyta
• Vascular tissue without specialization
• Pteridophyta
• Phanerogams
• Bare naked seeds
• Angiosperms
• Seeds with two cotyledons

50. Write the names of a few thallophytes. Draw a labelled diagram of Spirogyra.

Ulothrix, Spirogyra, Cladophara, Ulva and Chara are a few examples for Thallophytes

51. Thallophyta, bryophyta and pteridophyta are called as ‘Cryptogams’. Gymnosperms and Angiosperms are called as ‘phanerogams’. Discuss why? Draw one example of a Gymnosperm.

Thallophyta, bryophyta and pteridophyta are called as ‘Cryptogams’ because the reproductive organs of plants in all these three groups are very inconspicuous, and they are therefore called ‘cryptogams’, or ‘those with hidden reproductive organs’. In these plants, seeds are absent.

Example : Pinus

Gymnosperms and Angiosperms are called as ‘phanerogams’ because these are the plants with well-differentiated reproductive parts that ultimately make seeds.

Example: Cycas

52. Define the terms and give one example of each

(a) Bilateral symmetry

(c) Triploblastic

• An organism with body shapes that are mirror images along a middle line. The internal organs, however, are not necessarily distributed symmetrically. Example: Liver fluke
• The coelom is a body cavity filled with fluid. Fluid runs the complete length of vertebrates to divide the body of an organism into the inner tube, and the outer tube is called Coelom Example: Butterfly
• Animals that have 3 embryonic cell layers from which differentiated tissues are made are called triploblastic organisms. For example, Starfish

53. You are given leech, Nereis, Scolopendra, prawn and scorpion, and all have segmented body organisation. Will you classify them into one group? If no, give the important characters based on which you will separate these organisms into different groups.

The organisms given in the question do not belong to a common group of organisms. Leech and Nereis are annelids, but Scolopendra, prawn and scorpion are arthropods

Annelids have a metamerically segmented body. A metamerically segmented body is divided into many segments internally by septa. From head to tail, body segments are lined up one after the other. Arthropods have jointed legs and an open circulating system.

54. Which organism is more complex and evolved among Bacteria, Mushroom and Mango tree? Give reasons.

Among Bacteria, Mushroom and Mango Tree: The mango tree is a complex and evolved organism because it is a Eukaryotic, multicellular, autotrophic terrestrial plant. It is an angiosperm, and its seeds are covered within the ovary. Its reproductive organs accumulate in flower hence it is called a flowering plant.

Bacteria are prokaryotic unicellular organisms, and fungi are heterotrophic thallophytes with no body differentiation. Hence the mango tree evolved more than bacteria and fungi.

55. Differentiate between flying lizard and bird. Draw the diagram.

56. List out some common features in cat, rat and bat.

• All are Eukaryotes
• They are multicellular
• They are heterotrophic in nature
• All Have Notochord
• Presence of four-chambered heart
• Have a dorsal nerve cord
• All are triploblastic
• Have paired gill pouches
• They are coelomate.

57. Why do we keep both snake and turtle in the same class?

Because both have a certain common feature which is listed below.

• These animals are cold-blooded
• They have scales and breathe through the lungs
• Both of them have a three-chambered heart
• Both of them lay eggs with tough coverings and do not need to lay their eggs in water

Concepts Covered in NCERT Exemplar Solutions for Class 9 Science Chapter 7

• Introduction
• Classification
• Importance of classification
• Basis of classification
• Classification system
• 5 kingdom classification
• 2 kingdom classification
• Order of classification
• Types of cellular organisation
• Body organization
• Method of obtaining food
• 5 kingdom classification –
• Porifera or sponges
• Coelenterata
• Protochordata
• Cold blood organisms
• Warmblood organisms
• Nomenclature
• Conventions in writing scientific names

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Scientists Propose a Groundbreaking Evolutionary Law: The Increase of Functional Information

R esearchers have recently put forward a new scientific law termed “the law of increasing functional information,” which proposes a universal mechanism for the evolution of complex systems, encompassing life forms, minerals, stars, and more. This concept suggests that the complexity and diversity we observe in the natural world are not limited to living organisms but extend to the universe as a whole.

The law postulates that systems composed of numerous components—such as atoms, molecules, and cells—undergo evolution when many different configurations undergo selection for one or more functions. In a published study in the journal PNAS, the researchers state, “the functional information of a system will increase (i.e., the system will evolve) if many different configurations of the system undergo selection for one or more functions.”

This new law builds upon the principles of Darwinian evolution, extending the concept to non-living systems. As these systems’ components can be rearranged to form countless configurations, the configurations that enhance the system’s function are the ones that prevail. Functions may range from stability, which refers to the persistence of certain molecular arrangements, to the ability to harness energy continuously, to the generation of novelty, leading to new behaviors or characteristics.

An interdisciplinary team, comprising philosophers, astrobiologists, a theoretical physicist, a mineralogist, and a data scientist, worked collaboratively on this concept. “This was a true collaboration between scientists and philosophers to address one of the most profound mysteries of the cosmos: why do complex systems, including life, evolve toward greater functional information over time?” stated Jonathan Lunine, a physical science professor at Cornell University.

This proposal has elicited a variety of responses from the scientific community. Theoretical biologist Stuart Kauffman described the article as “superb, bold, broad, and transformational,” reflecting the importance of this research across different fields. Milan Cirkovic, a research professor at the Astronomical Observatory of Belgrade, praised it as “a breeze of fresh air blowing over the difficult terrain at the trijunction of astrobiology, systems science and evolutionary theory.” However, some, like astronomer Martin Rees, remain skeptical of the necessity for this new law, emphasizing the roles of physics and chemistry in generating diversity without the need for an analogous principle to Darwinian selection.

The implications of this proposed law are vast, with potential repercussions for our understanding of how life and complex systems evolve and the search for extraterrestrial life. If the increasing functionality of evolving systems is indeed guided by a natural law, life may be an expected outcome of planetary evolution rather than a rare occurrence.

Relevant articles:

– Scientists propose ‘missing’ law for the evolution of … , Space.com, Oct 21, 2023

– Scientists propose ‘missing’ law for the evolution of everything in the universe , Space.com

– Nature’s missing evolutionary law identified , Cornell University

– Scientists Unveil Nature’s Missing Evolutionary Law , Sci.News, Oct 18, 2023

Finished Papers

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NASA Is Recruiting a New Class of Astronauts

Victor Glover, a nine-year veteran of the astronaut corps who will fly around the moon in 2025, said the search for excellence and diversity were not mutually exclusive.

By Kenneth Chang and Emma Goldberg

The reporters interviewed a NASA official and an astronaut in The Times’s newsroom for this article.

Do you dream of leaving the planet?

NASA is looking for its next group of astronauts, and you have until April 2 to make a pitch for yourself .

“Typically, it’s a very popular application,” April Jordan, NASA’s astronaut selection manager, said.

The odds that you will be chosen are slim. The last time NASA put out a call for applications, in 2020, more than 12,000 people applied.

It took the agency a year and a half to go through the applications. NASA selected just 10 of the hopefuls, or 0.083 percent. That makes Harvard’s 3.5 percent acceptance rate among high school applicants appear bountiful.

“So when I say ‘popular,’” Ms. Jordan said, “it’s probably an understatement.”

Ms. Jordan is on a media tour to spread the word that “ the right stuff ” for being an astronaut in 2024 is not the same as what it was in the 1960s, when astronauts were all white men, almost all from the military.

Joining her on that tour, which included a stop at The New York Times, was Victor Glover, a nine-year veteran of the astronaut corps who offered a glimpse into how he made it through the rigorous selection process.

To become a NASA astronaut today, you have to be a U.S. citizen and you must pass the astronaut physical exam.

NASA does set a fairly high bar for education — a master’s degree in science, technology, engineering or mathematics, followed by at least three years of related professional experience.

Beyond that, the agency tries to keep an open mind. (There is no age limit, for example, or a requirement for 20/20 vision.)

“We want the group of astronaut candidates that we select to be reflective of the nation that they’re representing,” Ms. Jordan said.

Take, for example, Mr. Glover.

In some aspects, he fits the historical archetype. Before NASA, he was a Navy aviator and trained as a test pilot.

He is also breaking historical barriers.

In 2020, he became the first Black astronaut to serve as a crew member on the International Space Station after 20 years of astronauts living there. In 2025, he will become the first Black astronaut to fly around the moon for the Artemis II mission .

To stand out in NASA’s competitive application process, Mr. Glover knew he would need more than a strong résumé. He was particularly set on landing a good joke.

The night before one of Mr. Glover’s interviews at NASA for the 2013 class, he was asked to write an essay. The title: “Girls Like Astronauts.”

“They’re sitting in this room all day listening to all these dry answers,” he recalled thinking. “I’m going to try to make them laugh.”

The essay pivoted from a punchline to poignancy, reflecting on the ways he has tried to inspire his four daughters. He also decided to be vulnerable during the interview, sharing a “bone-headed” moment when he risked nearly hitting the water during an air show demonstration.

“You have to be able to share that information with the interview panel when you come in, because you’re inevitably going to fail at something,” Ms. Jordan said. “And so there’s a humbleness that you have to bring in even if you’ve achieved great things.”

As part of the application process, Mr. Glover wrote a limerick that concluded: “This is all dizzying to me, because I gave so much blood and pee.”

Mr. Glover set his sights on going to outer space as a child, when he saw his classmates moved to tears by the Challenger disaster.

His space ambition deepened years later when he heard a speech from Pam Melroy, a former space shuttle commander. Ms. Melroy, now NASA’s deputy administrator, recounted how her crew had scrambled to fix a damaged solar array on the International Space Station.

“I thought, ‘Wow, she just talked about something really technical, really logistically challenging,’” Mr. Glover said. “But the emotion in it was about the people.”

He realized, then, that just as astronauts need technical ability, they also need something that is more difficult to teach: social skills.

“You’re going to live in this tin can with somebody for six months,” he said of a stay on the space station. “We’re almost picking family members.”

Mr. Glover proudly points to the diversity of backgrounds among current astronauts. “If you compare our office to the country’s demographics, we match the country very well,” he said.

Indeed, the diversity within NASA outpaces that of the private sector in some aspects. The percentage of Black astronauts is higher than the percentage of Black people in the broader science and technology work force, Mr. Glover said.

That is the direct result of NASA’s sustained efforts over a couple of decades to recruit astronauts beyond the traditional archetype, he said.

“Our office looks the way it looks because of this intentionality, and thinking about our biases and how it may affect who we hire,” he said. “I think that’s a huge victory.”

But Mr. Glover acknowledged that diversity as a hiring goal was becoming increasingly fraught .

Critics include Elon Musk, the billionaire who runs SpaceX, the rocket company that NASA relies on to transport cargo and astronauts — like Mr. Glover — to the International Space Station. NASA has also hired SpaceX to land astronauts on the moon .

“His perspective on some things is a little disturbing,” Mr. Glover said of Mr. Musk.

SpaceX did not respond to a request for comment by Mr. Musk.

Mr. Musk has repeatedly called for the end of programs that focus on diversity, equity and inclusion, or D.E.I. “D.E.I. is just another word for racism,” he posted in January on X, the social media network that he owns.

Mr. Glover said he had just listened to a contentious interview that Don Lemon , a former CNN anchor, recently conducted with Mr. Musk. “My mom sent it to me and she goes, ‘Does he remember you rode in his spaceship?’” he said. “I’m like, ‘Ma, he probably remembers very vividly.’ He’s a great intellect, but he probably just doesn’t care.”

People ask him how he feels about becoming the first Black person to go on a lunar mission next year when Artemis II will swing around the moon without landing.

“Actually, I’m sad,” Mr. Glover said. “It’s 2025, and I’m going to be the first? Come on.”

He recounted the story of Ed Dwight , the only Black Air Force pilot in the 1960s who met the restrictive requirements that NASA had for astronauts then. But Mr. Dwight was never selected.

“Ed Dwight could have done this in the ’60s,” Mr. Glover said. “How much better would our country be if he actually got the chance? Society wasn’t ready. It’s not him. He was ready.”

While Mr. Glover has heard some of the pushback to D.E.I. initiatives, he feels firmly that seeking diversity is not about lowering standards and accepting less qualified candidates. “I think it should just be excellence,” he said. “As long as you don’t equate whiteness or maleness with excellence, then we’re good. We’re speaking the same language.”

Many applicants are drawn by the potential glory of being the first astronauts to walk on Mars, an accomplishment that NASA is aiming for in the 2030s.

But Mr. Glover said they should also contemplate the sacrifices that they and their families might have to make along the way.

“The trip to Mars is six to nine months,” he said. “You’re going to be away from familiar for more than a year, one to three years. Are you really ready for that?”

Kenneth Chang , a science reporter at The Times, covers NASA and the solar system, and research closer to Earth. More about Kenneth Chang

Emma Goldberg is a business reporter covering workplace culture and the ways work is evolving in a time of social and technological change. More about Emma Goldberg

What’s Up in Space and Astronomy

Keep track of things going on in our solar system and all around the universe..

Never miss an eclipse, a meteor shower, a rocket launch or any other 2024 event  that’s out of this world with  our space and astronomy calendar .

A new set of computer simulations, which take into account the effects of stars moving past our solar system, has effectively made it harder to predict Earth’s future and reconstruct its past.

Dante Lauretta, the planetary scientist who led the OSIRIS-REx mission to retrieve a handful of space dust , discusses his next final frontier.

A nova named T Coronae Borealis lit up the night about 80 years ago. Astronomers say it’s expected to put on another show  in the coming months.

Voyager 1, the 46-year-old first craft in interstellar space which flew by Jupiter and Saturn in its youth, may have gone dark .

Is Pluto a planet? And what is a planet, anyway? Test your knowledge here .

Cross-Cultural Psychology

Living and loving in a diverse society, intercultural relationships can be very happy if approached properly..

Posted April 3, 2024 | Reviewed by Davia Sills

• Researchers have identified three different ways of thinking about diversity.
• The ways that intercultural couples think about diversity can impact relationship satisfaction.
• Likewise, it affects their children’s personality and self-identity formation.

North America has long been a melting pot of cultures as centuries of immigrants came to settle in the New World. But the attitude has long been that people should stick to their own kind, both in friendship and in romance.

Certainly, there have always been those who fell in love across racial or ethnic boundaries , but it was long believed that such “mixed marriages” were doomed to failure. And thanks to the discrimination and ostracism these couples faced, this often became a self-fulfilling prophecy.

In recent years, however, attitudes have changed, and society has become accepting of racial and ethnic diversity in neighborhoods, at work, among friends, and even between lovers. And with this change in social attitudes, more and more people are seeking relationships outside their own culture. That is, they view compatibility more in terms of personality than superficial features like skin color or ethnic group.

Ways of Thinking About Diversity

It appears that today’s youth are largely accepting of differences in race and ethnicity , especially in more urban areas. However, as University of Toronto (Canada) psychologist Hanieh Naeimi and her colleagues point out in an article they recently published in the Journal of Social and Personal Relationships , there are various ways of thinking about diversity. Furthermore, they provide evidence from studies of intercultural couples that people’s diversity ideology can have a significant impact on the quality of their relationships.

Naeimi and her colleagues point out that past research has identified three types of diversity ideology:

• Colorblindness is the perspective that all people should be treated equally despite their cultural differences, which are seen as superficial. Deep down, according to this viewpoint, people are all the same, and cultural differences should be ignored. It calls on intercultural couples to act as though there were no meaningful cultural differences between them.
• Multiculturalism is an ideology that acknowledges cultural differences as real and significant but nevertheless worth learning about and celebrating. Like colorblindness, multiculturalism sees culture as an immutable part of a person, but unlike colorblindness, cultural differences should be accepted rather than ignored. It calls on intercultural couples to each maintain their own culture.
• Polyculturalism is similar to multiculturalism in that it accepts cultural differences as real and meaningful, but unlike multiculturalism or colorblindness, it sees culture as ever-evolving. It calls on intercultural couples to celebrate both cultures and even to blend them together.

In sum, each of these diversity ideologies provides a program for how intercultural couples should share their cultures with each other, both in terms of how each person expresses their own culture and how they accept their partner’s culture.

How Thinking About Diversity Affects Intercultural Relationships

In three studies, Naeimi and her colleagues investigated how diversity ideology impacted relationship outcomes through the practice of cultural sharing.

People who endorsed colorblindness tended to be less accepting of their partner’s culture, which resulted in less satisfaction and more conflict in their relationship. Because they claim to see no significant differences between cultures, they tend to assume that their partner’s culture is pretty much the same as their own, which can come across as dismissive. The researchers noted that this was less of a problem for couples whose cultures are similar, but conflict and dissatisfaction increase when the cultures are farther apart or if there has been significant historical discord between the two heritages.

Overall, people who endorsed multiculturalism showed greater acceptance of their partner’s culture and more willingness to express their own. In other words, they showed mutual respect for each other’s culture and traditions. As a result, they were happier in their relationships than were those who endorsed colorblindness.

However, the happiest relationships were those in which the partners endorsed polyculturalism. Not only do they respect each other’s cultures, but they also take part in each partner’s cultural activities and traditions. That is, the partners enjoy the food and music and celebrate the holidays and ceremonies of both cultures.

How Thinking About Diversity Affects Children of Intercultural Couples

The researchers also note that diversity ideology has an important impact on the personality development of the children of intercultural couples. When parents endorse colorblindness, the family’s culture tends to default to the dominant culture of the society in which they live. As a result, the children lose the cultural heritage of the other parent.

Likewise, children of parents who endorse multiculturalism will struggle with the formation of self- identity . They will ask if they belong to their mother’s or their father’s culture. Again, they’re most likely to default to the culture of the society in which they live.

Only when parents endorse polyculturalism will children benefit from their parents’ cultural diversity. These are the children who grow up to be adults who move seamlessly from one culture to the other and feel at ease in either one.

Living and loving in a diverse society requires all three diversity ideologies. Colorblindness teaches us to respect all persons as equals regardless of their cultural background. Multiculturalism raises our awareness and acceptance of the rich and colorful traditions and practices of each culture. And finally, polyculturalism encourages us to celebrate the diverse cultures of our friends and lovers and even make them our own.

Naeimi, H., West, A. L., Muise, A., Johnson, M. D., & Impett, E. A. (2023). Through the cultural looking glass: Diversity ideologies and cultural sharing in intercultural romantic relationships. Journal of Social and Personal Relationships . Advance online publication. DOI: 10.1177/02654075231208727

David Ludden, Ph.D. , is a professor of psychology at Georgia Gwinnett College.

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