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Evolutionary Biology is the study of history of life forms
on earth. What exactly is evolution? To understand the
changes in flora and fauna that have occurred over millions
of years on earth, we must have an understanding of the
context of origin of life, i.e., evolution of earth, of stars and
indeed of the universe itself. What follows is the longest of
all the construed and conjectured stories. This is the story
of origin of life and evolution of life forms or biodiversity on
planet earth in the context of evolution of earth and against
the background of evolution of universe itself.
7.1 ORIGIN OF LIFE
When we look at stars on a clear night sky we are, in a
way, looking back in time. Stellar distances are measured
in light years. What we see today is an object whose emitted
light started its journey millions of year back and from
trillions of kilometres away and reaching our eyes now.
However, when we see objects in our immediate
surroundings we see them instantly and hence in the
present time. Therefore, when we see stars we apparently
are peeping into the past.
The origin of life is considered a unique event in the
history of universe. The universe is vast. Relatively speaking
the earth itself is almost only a speck. The universe is very
CHAPTER 7
EVOLUTION
7.1 Origin of Life
7.2 Evolution of Life Forms - A
Theory
7.3 What are the Evidences
for Evolution?
7.4 What is Adaptive
Radiation?
7.5 Biological Evolution
7.6 Mechanism of Evolution
7.7 Hardy - Weinberg
Principle
7.8 A Brief Account of
Evolution
7.9 Origin and Evolution of
Man
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old – almost 20 billion years old. Huge clusters of galaxies comprise the
universe. Galaxies contain stars and clouds of gas and dust. Considering
the size of universe, earth is indeed a speck. The Big Bang theory attempts
to explain to us the origin of universe. It talks of a singular huge explosion
unimaginable in physical terms. The universe expanded and hence, the
temperature came down. Hydrogen and Helium formed sometime later.
The gases condensed under gravitation and formed the galaxies of the
present day universe. In the solar system of the milky way galaxy, earth
was supposed to have been formed about 4.5 billion years back. There
was no atmosphere on early earth. Water vapour, methane, carbondioxide
and ammonia released from molten mass covered the surface. The UV rays
from the sun brokeup water into Hydrogen and Oxygen and the lighter H
2
escaped. Oxygen combined with ammonia and methane to form water,
CO
2
and others. The ozone layer was formed. As it cooled, the water vapor
fell as rain, to fill all the depressions and form oceans. Life appeared 500
million years after the formation of earth, i.e., almost four billion years back.
Did life come from outerspace? Some scientists believe that it came
from outside. Early Greek thinkers thought units of life called
spores
were transferred to different planets including earth. ‘Panspermia’ is still
a favourite idea for some astronomers. For a long time it was also believed
that life came out of decaying and rotting matter like straw, mud, etc.
This was the theory of spontaneous generation. Louis Pasteur by careful
experimentation demonstrated that life comes only from pre-existing life.
He showed that in pre-sterilised flasks, life did not come from killed yeast
while in another flask open to air, new living organisms arose from ‘killed
yeast’. Spontaneous generation theory was dismissed once and for all.
However, this did not answer how the first life form came on earth.
Oparin of Russia and Haldane of England proposed that the first form
of life could have come from pre-existing non-living organic molecules
(e.g. RNA, protein, etc.) and that formation of life was preceded by chemical
evolution, i.e., formation of diverse organic molecules from inorganic
constituents. The conditions on earth were – high temperature, volcanic
storms, reducing atmosphere containing CH
4
, NH
3
, etc. In 1953, S.L. Miller,
an American scientist created similar conditions in a laboratory scale
(Figure 7.1). He created electric discharge in a closed flask containing
CH
4
, H
2
, NH
3
and water vapour at 800
0
C. He observed formation of amino
acids. In similar experiments others observed, formation of sugars,
nitrogen bases, pigment and fats. Analysis of meteorite content also
revealed similar compounds indicating that similar processes are
occurring elsewhere in space. With this limited evidence, the first part of
the conjectured story, i.e., chemical evolution was more or less accepted.
We have no idea about how the first self replicating metabolic capsule
of life arose. The first non-cellular forms of life could have originated
3 billion years back. They would have been giant molecules (RNA, Protein,
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Polysaccharides, etc.). These capsules reproduced their molecules perhaps.
The first cellular form of life did not possibly originate till about 2000
million years ago. These were probably single-cells. All life forms were in
water environment only. This version of a biogenesis, i.e., the first form of
life arose slowly through evolutionary forces from non-living molecules is
accepted by majority. However, once formed, how the first cellular forms
of life could have evolved into the complex biodiversity of today is the
fascinating story that will be discussed below.
7.2 EVOLUTION OF LIFE FORMS – A THEORY
Conventional religious literature tells us about the theory of special
creation. This theory has three connotations. One, that all living organisms
(species or types) that we see today were created as such. Two, that the
diversity was always the same since creation and will be the same in future
also. Three, that earth is about 4000 years old. All these ideas were
strongly challenged during the nineteenth century. Based on observations
made during a sea voyage in a sail ship called H.M.S. Beagle round the
world, Charles Darwin concluded that existing living forms share
similarities to varying degrees not only among themselves but also with
life forms that existed millions of years ago. Many such life forms do not
exist any more. There had been extinctions of different life forms in the
years gone by just as new forms of life arose at different periods of history
of earth. There has been gradual evolution of life forms. Any population
Figure 7.1 Diagrammatic representation of Miller’s
experiment
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has built in variation in characteristics. Those characteristics which enable
some to survive better in natural conditions (climate, food, physical factors,
etc.) would outbreed others that are less-endowed to survive under such
natural conditions. Another word used is fitness of the individual or
population. The fitness, according to Darwin, refers ultimately and only
to reproductive fitness. Hence, those who are better fit in an environment,
leave more progeny than others. These, therefore, will survive more and
hence are selected by nature. He called it natural selection and implied it
as a mechanism of evolution. Let us also remember that Alfred Wallace, a
naturalist who worked in Malay Archipelago had also come to similar
conclusions around the same time. In due course of time, apparently new
types of organisms are recognisable. All the existing life forms share
similarities and share common ancestors. However, these ancestors were
present at different periods in the history of earth (epochs, periods and
eras). The geological history of earth closely correlates with the biological
history of earth. A common permissible conclusion is that earth is very
old, not thousand of years as was thought earlier but billions of years old.
7.3 WHAT ARE THE EVIDENCES FOR EVOLUTION?
Evidence that evolution of life forms has indeed taken place on earth has
come from many quarters. Fossils are remains of hard parts of
life-forms found in rocks. Rocks form sediments and a cross-section of
earth's crust indicates the arrangement of sediments one over the other
during the long history of earth. Different-aged rock sediments contain
fossils of different life-forms who probably died during the formation of
the particular sediment. Some of them appear similar to modern
organisms (Figure 7.2). They represent extinct organisms (e.g., Dinosaurs).
A study of fossils in different sedimentary layers indicates the geological
period in which they existed. The study showed that life-forms varied
over time and certain life forms are restricted to certain geological time-
spans. Hence, new forms of life have arisen at different times in the history
of earth. All this is called paleontological evidence. Do you remember
how the ages of the fossils are calculated? Do you recollect the method
of radioactive-dating and the principles behind the procedure?
Embryological support for evolution was also proposed by Ernst
Heckel based upon the observation of certain features during embryonic
stage common to all vertebrates that are absent in adult. For example,
the embryos of all vertebrates including human develop a row of vestigial
gill slit just behind the head but it is a functional organ only in fish and
not found in any other adult vertebrates. However, this proposal was
disapproved on careful study performed by Karl Ernst von Baer. He noted
that embryos never pass through the adult stages of other animals.
Comparative anatomy and morphology shows similarities and
differences among organisms of today and those that existed years ago.
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Figure 7.2 A family tree of dinosaurs and their living modern day counterpart organisms like
crocodiles and birds
Such similarities can be interpreted to understand whether common
ancestors were shared or not. For example whales, bats, Cheetah and
human (all mammals) share similarities in the pattern of bones of forelimbs
(Figure 7.3b). Though these forelimbs perform different functions in these
animals, they have similar anatomical structure – all of them have
humerus, radius, ulna, carpals, metacarpals and phalanges in their
forelimbs. Hence, in these animals, the same structure developed along
different directions due to adaptations to different needs. This is divergent
evolution and these structures are homologous. Homology indicates
common ancestry. Other examples are vertebrate hearts or brains. In
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plants also, the thorn and tendrils of
Bougainvillea and Cucurbita represent
homology (Figure 7.3a). Homology is
based on divergent evolution whereas
analogy refers to a situation exactly
opposite. Wings of butterfly and of birds
look alike. They are not anatomically
similar structures though they perform
similar functions. Hence, analogous
structures are a result of convergent
evolution - different structures evolving
for the same function and hence having
similarity. Other examples of analogy are
the eye of the octopus and of mammals
or the flippers of Penguins and Dolphins.
One can say that it is the similar habitat
that has resulted in selection of similar
adaptive features in different groups of
organisms but toward the same function:
Sweet potato (root modification) and
potato (stem modification) is another
example for analogy.
In the same line of argument,
similarities in proteins and genes
performing a given function among diverse
organisms give clues to common ancestry.
These biochemical similarities point to the
same shared ancestry as structural
similarities among diverse organisms.
Man has bred selected plants and
animals for agriculture, horticulture, sport
or security. Man has domesticated many
wild animals and crops. This intensive
breeding programme has created breeds
that differ from other breeds (e.g., dogs) but
still are of the same group. It is argued that
if within hundreds of years, man could create new breeds, could not nature
have done the same over millions of years?
Another interesting observation supporting evolution by natural
selection comes from England. In a collection of moths made in 1850s,
i.e., before industrialisation set in, it was observed that there were more
white-winged moths on trees than dark-winged or melanised moths.
However, in the collection carried out from the same area, but after
industrialisation, i.e., in 1920, there were more dark-winged moths in
the same area, i.e., the proportion was reversed.
(b)
Figure 7.3 Example of homologous organs in
(a) Plants and (b) Animals
(a)
Tendril
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The explanation put forth for this observation was that ‘predators will
spot a moth against a contrasting background’. During post-
industrialisation period, the tree trunks became dark due to industrial
smoke and soots. Under this condition the white-winged moth did not
survive due to predators, dark-winged or melanised moth survived. Before
industrialisation set in, thick growth of almost white-coloured lichen
covered the trees - in that background the white winged moth survived
but the dark-coloured moth were picked out by predators. Do you know
that lichens can be used as industrial pollution indicators? They will
not grow in areas that are polluted. Hence, moths that were able to
camouflage themselves, i.e., hide in the background, survived
(Figure 7.4). This understanding is supported by the fact that in areas
where industrialisation did not occur e.g., in rural areas, the count of
melanic moths was low. This showed that in a mixed population, those
that can better-adapt, survive and increase in population size. Remember
that no variant is completely wiped out.
Similarly, excess use of herbicides, pesticides, etc., has only resulted in
selection of resistant varieties in a much lesser time scale. This is also true for
microbes against which we employ antibiotics or drugs against eukaryotic
organisms/cell. Hence, resistant organisms/cells are appearing in a time
scale of months or years and not centuries. These are examples of evolution
by anthropogenic action. This also tells us that evolution is not a directed
process in the sense of determinism. It is a stochastic process based on
chance events in nature and chance mutation in the organisms.
7.4 WHAT IS ADAPTIVE RADIATION?
During his journey Darwin went to Galapagos Islands. There he observed
an amazing diversity of creatures. Of particular interest, small black birds
later called Darwin’s Finches amazed him. He realised that there were many
Figure 7.4 Figure showing white - winged moth and dark - winged moth (melanised)
on a tree trunk (a) In unpolluted area (b) In polluted area
(a)
(b)
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varieties of finches in the same island. All the varieties, he conjectured,
evolved on the island itself. From the original seed-eating features, many
other forms with altered beaks arose, enabling them to become insectivorous
and vegetarian finches (Figure 7.5). This process of evolution of different
species in a given geographical area starting from a point and literally
radiating to other areas of geography (habitats) is called adaptive radiation.
Darwin’s finches represent one of the best examples of this phenomenon.
Another example is Australian marsupials. A number of marsupials, each
different from the other (Figure 7.6) evolved from an ancestral stock, but all
within the Australian island continent. When more than one adaptive radiation
appeared to have occurred in an isolated geographical area (representing
Figure 7.6 Adaptive radiation of marsupials of Australia
Figure 7.5
Variety of beaks of finches that Darwin found in Galapagos Island
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different habitats), one can call this convergent
evolution. Placental mammals in Australia also
exhibit adaptive radiation in evolving into
varieties of such placental mammals each of
which appears to be ‘similar’ to a corresponding
marsupial (e.g.,
Placental wolf and Tasmanian
wolf-marsupial). (Figure 7.7).
7.5 BIOLOGICAL EVOLUTION
Evolution by natural selection, in a true sense
would have started when cellular forms of life
with differences in metabolic capability
originated on earth.
The essence of Darwinian theory about
evolution is natural selection. The rate of
appearance of new forms is linked to the life cycle
or the life span. Microbes that divide fast have
the ability to multiply and become millions of
individuals within hours. A colony of bacteria
(say A) growing on a given medium has built-in
variation in terms of ability to utilise a feed
component. A change in the medium
composition would bring out only that part of
the population (say B) that can survive under
the new conditions. In due course of time this
variant population outgrows the others and
appears as new species. This would happen
within days. For the same thing to happen in a
fish or fowl would take million of years as life
spans of these animals are in years. Here we say
that fitness of B is better than that of A under
the new conditions. Nature selects for fitness.
One must remember that the so-called fitness is
based on characteristics which are inherited.
Hence, there must be a genetic basis for getting selected and to evolve.
Another way of saying the same thing is that some organisms are better
adapted to survive in an otherwise hostile environment. Adaptive ability is
inherited. It has a genetic basis. Fitness is the end result of the ability to
adapt and get selected by nature.
Branching descent and natural selection are the two key concepts
of Darwinian Theory of Evolution (Figures 7.7 and 7.8).
Even before Darwin, a French naturalist Lamarck had said that
evolution of life forms had occurred but driven by use and disuse of
Figure 7.7 Picture showing convergent evolution
of Australian Marsupials and
placental mammals
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organs. He gave the examples of Giraffes who in an attempt to forage
leaves on tall trees had to adapt by elongation of their necks. As they
passed on this acquired character of elongated neck to succeeding
generations, Giraffes, slowly, over the years, came to acquire long necks.
Nobody believes this conjecture any more.
Is evolution a process or the result of a process? The world we see,
inanimate and animate, is only the success stories of evolution. When we
describe the story of this world we describe evolution as a process. On the
other hand when we describe the story of life on earth, we treat evolution
as a consequence of a process called natural selection. We are still not
very clear whether to regard evolution and natural selection as processes
or end result of unknown processes.
It is possible that the work of Thomas Malthus on populations
influenced Darwin. Natural selection is based on certain observations
which are factual. For example, natural resources are limited, populations
are stable in size except for seasonal fluctuation, members of a population
vary in characteristics (infact no two individuals are alike) even though
they look superficially similar, most of variations are inherited etc. The
fact that theoretically population size will grow exponentially if everybody
reproduced maximally (this fact can be seen in a growing bacterial
population) and the fact that population sizes in reality are limited, means
that there had been competition for resources. Only some survived and
grew at the cost of others that could not flourish. The novelty and brilliant
insight of Darwin was this: he asserted that variations, which are heritable
and which make resource utilisation better for few (adapted to habitat
better) will enable only those to reproduce and leave more progeny. Hence
for a period of time, over many generations, survivors will leave more
progeny and there would be a change in population characteristic and
hence new forms appear to arise.
7.6 MECHANISM OF EVOLUTION
What is the origin of this variation and how does speciation occur? Even
though Mendel had talked of inheritable 'factors' influencing phenotype,
Darwin either ignored these observations or kept silence. In the first decade
of twentieth century, Hugo deVries based on his work on evening primrose
brought forth the idea of mutations – large difference arising suddenly in
a population. He believed that it is mutation which causes evolution and
not the minor variations (heritable) that Darwin talked about. Mutations
are random and directionless while Darwinian variations are small and
directional. Evolution for Darwin was gradual while deVries believed
mutation caused speciation and hence called it
saltation (single step
large mutation). Studies in population genetics, later, brought out
some clarity.
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Figure 7.8 Diagrammatic representation of the operation of natural selection on different
traits : (a) Stabilising (b) Directional and (c) Disruptive
(a)
(b)
(c)
7.7 HARDY-WEINBERG PRINCIPLE
In a given population one can find out the frequency of occurrence of
alleles of a gene or a locus. This frequency is supposed to remain fixed
and even remain the same through generations. Hardy-Weinberg principle
stated it using algebraic equations.
This principle says that allele frequencies in a population are stable
and is constant from generation to generation. The gene pool (total genes
and their alleles in a population) remains a constant. This is called
genetic equilibrium. Sum total of all the allelic frequencies is 1. Individual
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frequencies, for example, can be named p, q, etc. In a diploid, p and q
represent the frequency of allele A and allele a. The frequency of AA
individuals in a population is simply p
2
. This is simply stated in another
ways, i.e., the probability that an allele A with a frequency of p appear on
both the chromosomes of a diploid individual is simply the product
of the probabilities, i.e., p
2
. Similarly of aa is q
2
, of Aa 2pq. Hence,
p
2
+2pq+q
2
=1. This is a binomial expansion of (p+q)
2
. When frequency
measured, differs from expected values, the difference (direction) indicates
the extent of evolutionary change. Disturbance in genetic equilibrium, or
Hardy- Weinberg equilibrium, i.e., change of frequency of alleles in a
population would then be interpreted as resulting in evolution.
Five factors are known to affect Hardy-Weinberg equilibrium. These
are gene migration or gene flow, genetic drift, mutation, genetic
recombination and natural selection. When migration of a section of
population to another place and population occurs, gene frequencies
change in the original as well as in the new population. New genes/alleles
are added to the new population and these are lost from the old population.
There would be a gene flow if this gene migration, happens multiple times.
If the same change occurs by chance, it is called genetic drift. Sometimes
the change in allele frequency is so different in the new sample of population
that they become a different species. The original drifted population
becomes founders and the effect is called founder effect.
Microbial experiments show that pre-existing advantageous
mutations when selected will result in observation of new phenotypes.
Over few generations, this would result in Speciation. Natural selection is
a process in which heritable variations enabling better survival are enabled
to reproduce and leave greater number of progeny. A critical analysis
makes us believe that variation due to mutation or variation due to
recombination during gametogenesis, or due to gene flow or genetic drift
results in changed frequency of genes and alleles in future generation.
Coupled to enhance reproductive success, natural selection makes it look
like different population. Natural selection can lead to stabilisation (in
which more individuals acquire mean character value), directional change
(more individuals acquire value other than the mean character value) or
disruption (more individuals acquire peripheral character value at both
ends of the distribution curve) (Figure 7.8).
7.8 A BRIEF ACCOUNT
OF EVOLUTION
About 2000 million years ago (mya) the first cellular forms of life appeared
on earth. The mechanism of how non-cellular aggregates of giant
macromolecules could evolve into cells with membranous envelop is not
known. Some of these cells had the ability to release O
2
. The reaction
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Figure 7.9 A sketch of the evolution of plant forms through geological periods
could have been similar to the light reaction in photosynthesis where water
is split with the help of solar energy captured and channelised by
appropriate light harvesting pigments. Slowly single-celled organisms
became multi-cellular life forms. By the time of 500 mya, invertebrates
were formed and active. Jawless fish probably evolved around 350 mya.
Sea weeds and few plants existed probably around 320 mya. We are told
that the first organisms that invaded land were plants. They were
widespread on land when animals invaded land. Fish with stout and strong
fins could move on land and go back to water. This was about 350 mya. In
1938, a fish caught in South Africa happened to be a Coelacanth which was
thought to be extinct. These animals called lobefins evolved into the
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first amphibians that lived on both land and water. There are no specimens
of these left with us. However, these were ancestors of modern day frogs
and salamanders. The amphibians evolved into reptiles. They lay thick-
shelled eggs which do not dry up in sun unlike those of amphibians.
Again we only see their modern day descendents, the turtles, tortoises
and crocodiles. In the next 200 millions years or so, reptiles of different
Figure 7.10 Representative evolutionary history of vertebrates through geological periods
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shapes and sizes dominated on earth. Giant ferns (pteridophytes) were
present but they all fell to form coal deposits slowly. Some of these land
reptiles went back into water to evolve into fish like reptiles probably 200
mya (e.g. Ichthyosaurs). The land reptiles were, of course, the dinosaurs.
The biggest of them, i.e., Tyrannosaurus rex was about 20 feet in height
and had huge fearsome dagger like teeth. About 65 mya, the dinosaurs
suddenly disappeared from the earth. We do not know the true reason.
Some say climatic changes killed them. Some say most of them evolved
into birds. The truth may live in between. Small sized reptiles of that era
still exist today.
The first mammals were like shrews. Their fossils are small sized.
Mammals were viviparous and protected their unborn young inside the
mother’s body. Mammals were more intelligent in sensing and avoiding
danger at least. When reptiles came down mammals took over this earth.
There were in South America mammals resembling horse, hippopotamus,
bear, rabbit, etc. Due to continental drift, when South America joined
North America, these animals were overridden by North American fauna.
Due to the same continental drift pouched mammals of Australia survived
because of lack of competition from any other mammal.
Lest we forget, some mammals live wholly in water. Whales, dolphins,
seals and sea cows are some examples. Evolution of horse, elephant, dog,
etc., are special stories of evolution. You will learn about these in higher
classes. The most successful story is the evolution of man with language
skills and self-consciousness.
A rough sketch of the evolution of life forms, their times on a geological
scale are indicated in (Figure 7.9 and 7.10).
7.9 ORIGIN AND EVOLUTION OF MAN
About 15 mya, primates called Dryopithecus and Ramapithecus were
existing. They were hairy and walked like gorillas and chimpanzees.
Ramapithecus was more man-like while Dryopithecus was more
ape-like. Few fossils of man-like bones have been discovered in Ethiopia
and Tanzania (Figure 7.11). These revealed hominid features leading to
the belief that about 3-4 mya, man-like primates walked in eastern Africa.
They were probably not taller than 4 feet but walked up right. Two mya,
Australopithecines probably lived in East African grasslands. Evidence
shows they hunted with stone weapons but essentially ate fruit. Some of
the bones among the bones discovered were different. This creature was
called the first human-like being the hominid and was called Homo habilis.
The brain capacities were between 650-800cc. They probably did not eat
meat. Fossils discovered in Java in 1891 revealed the next stage, i.e., Homo
erectus about 1.5 mya. Homo erectus
had a large brain around 900cc.
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Figure 7.11 A comparison of the skulls of adult modern human being, baby chimpanzee and
adult chimpanzee. The skull of baby chimpanzee is more like adult human skull
than adult chimpanzee skull
Homo erectus probably ate meat. The Neanderthal man with a brain size
of 1400cc lived in near east and central Asia between 1,00,000-40,000
years back. They used hides to protect their body and buried their dead.
Homo sapiens arose in Africa and moved across continents and developed
into distinct races. During ice age between 75,000-10,000 years ago
modern Homo sapiens arose. Pre-historic cave art developed about
18,000 years ago. One such cave paintings by Pre-historic humans can
be seen at Bhimbetka rock shelter in Raisen district of Madhya Pradesh.
Agriculture came around 10,000 years back and human settlements
started. The rest of what happened is part of human history of growth
and decline of civilisations.
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EXERCISES
1. Explain antibiotic resistance observed in bacteria in light of Darwinian
selection theory.
2. Find out from newspapers and popular science articles any new fossil
discoveries or controversies about evolution.
3. Attempt giving a clear definition of the term species.
4. Try to trace the various components of human evolution (hint: brain
size and function, skeletal structure, dietary preference, etc.)
5. Find out through internet and popular science articles whether animals
other than man has self-consciousness.
6. List 10 modern-day animals and using the internet resources link it to
a corresponding ancient fossil. Name both.
7. Practise drawing various animals and plants.
8. Describe one example of adaptive radiation.
9. Can we call human evolution as adaptive radiation?
10. Using various resources such as your school Library or the internet
and discussions with your teacher, trace the evolutionary stages of
any one animal, say horse.
SUMMARY
The origin of life on earth can be understood only against the
background of origin of universe especially earth. Most scientists
believe chemical evolution, i.e., formation of biomolecules preceded
the appearance of the first cellular forms of life. The subsequent events
as to what happened to the first form of life is a conjectured story
based on Darwinian ideas of organic evolution by natural selection.
Diversity of life forms on earth has been changing over millions of
years. It is generally believed that variations in a population result in
variable fitness. Other phenomena like habitat fragmentation and
genetic drift may accentuate these variations leading to appearance
of new species and hence evolution. Homology is accounted for by the
idea of branching descent. Study of comparative anatomy, fossils and
comparative biochemistry provides evidence for evolution. Among the
stories of evolution of individual species, the story of evolution of
modern man is most interesting and appears to parallel evolution of
human brain and language.
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