Theory of Evolution

2. EVOLUTIONby Suvam Dutta

3. Introduction
◦ Evolutionary biology is the study of history of life forms on earth. Evolution
simply means an orderly change from one condition to another. It is the
changes in flora and fauna (plants and animals) that have occurred over millions of
years on earth.

4. Development of Modern Evolutionary Theory:

5. Biological Evolution
❖ Lamarck’s Theory –
Lamarck published his theory of evolution in 'Philosophie Zoologique' in 1809. It is
popularly known as 'The inheritance of acquired characters in organisms’. Lamarckism
can be defined as "the changes in structure or function of any organ acquired during the
lifetime of an individual in response to changes in the surrounding environment which
are inherited by its offspring and keep on adding up over a period of time".

6. Four main proposition of Lamarckism are:
(i) Internal vital force: All the living things and their component parts are continually increased due to
internal vital force.
(ii) Effect of environment and new needs: A change in environment brings about changes in organisms
and gives rise to new needs. New needs or desires produce new structures and change the habits of
organisms. Doctrine of desires is called appetency.
(iii)Use and disuse of organs: If an organ is constantly used, then it would be better developed, whereas
disuse of organ results in its degeneration.
(iv)Inheritance of acquired characters: Characters that an individual acquires during its lifetime due to
internal vital force, effect of environment, new needs and use and disuse of organs, are inherited
(transmitted) to the next generations. The process continues and after several generations, the variations
are accumulated upto such an extent that they give rise to new species.

7. ExamplE of lamarck’s thEory

8. Criticism of Lamarckism
◦ Lamarck's theory of inheritance of acquired characters was disapproved by a
German biologist August Weismann. He cited many examples and put forth the
theory of continuity of germplasm. According to this theory, the characters
influencing the germ cells are only inherited. Weismann cut off the tails of rats for
as many as 22 generations and allowed them to breed, but tailless rats were never
born.

9. Darwin’s thEory:
◦ Charles Darwin, an English naturalist and one of the most important biologists of 19th century made an
extensive study of nature for over 20 years while on a voyage of world exploration on a famous ship
H.M.S. Beagle. During this journey, he explored the fauna and flora of a number of continents and
islands such as Galapagos islands. There he observed great variations among the organisms living there
and called it "a living laboratory of evolution.“
◦ The theory of natural selection was announced on June 30, 1858 by the English naturalist Charles
Darwin (1809-1882) and Alfred Russel Wallace (1823-1913) in the paper 'Origin of Species by Means
of Natural Selection".

10. Although the idea of evolution was not new, Darwin and Wallace presented the most complete evidence yet
seen to support evolution. They also presented the mechanism, natural selection, by which evolution
occurred.
Darwin cited the following evidence for this theory:
◦ Geological evidence indicated that the Earth was very old, thereby providing sufficient time for evolution to
occur.
◦ Many fossil life forms looked like present day organisms. Some fossils (e.g. horses) show a progression of
changes over time.
◦ Embryos of diverse organisms (fish, reptiles, birds, mammals, etc.) resemble each other.
◦ Most organisms share a common body plan. Furthermore, various anatomical structures of diverse
organisms had similar compositions (e.g. bones of bat wing, reptile forearm, fish fin).
◦ Many geographically isolated species are similar (horses and zebras, land and marine iguanas, finches and
tortoises on the various Galapagos Islands).
◦ Humans had been selectively breeding organisms (e.g. cattle, chickens, dogs, wheat, corn) to create breeds
with desired traits for thousands of years. Why couldn't nature do the same thing over millions or billions of
years?

11. Natural selection explained by Darwin
◦ 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.
Salient features of Darwin's theory of natural selection:
I. Rapid multiplication.
II. Struggle for existence.
III. Survival of the fittest.
IV. Formation of new species.
V. Inheritance of useful variations.
VI. Limited food and space.
VII. Inheritance of useful variations.

12. Industrial melanism
◦ Industrial melanism is an evolutionary effect prominent in several arthropods, where dark pigmentation has evolved
in an environment affected by industrial pollution, including sulphur dioxide gas and dark soot deposits.
◦ Industrial melanism is a striking example of the natural selection in the process of evolution. This was studied by
R.A. Fischer, E.B. Ford and H.B.D. Kettlewell. It is the appearance of dark melanic forms of some organisms like
moths in the industrial regions where soot emission from burning of coal has been heavy so as to colour the
background. Kettlewell (1958) has reported melanic forms of 70 species of moths from Britain and Europe. The
best studied type is peppered moth (Biston betularia).
▸ Industrial melanism can be written briefly as follow:
The peppered moth exists in two strains (forms): the light grey Biston betularia typica is creamy white with dark
blotches and spots and Biston betularia carbonaria the melanic form is supposed to be a mutant form that arose by
mutation in a single gene determining colouration. In the past, bark of trees was covered by whitish lichens, so white
moths escaped unnoticed from predatory birds. After industrialisation barks got covered by smoke, so the white moths
were selectively picked up by birds. But black moths escaped unnoticed so they managed to survive resulting in more
population of black moths and less population of white moths.

13. Industrial melanism

14. Adaptive radiation
◦ The 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 of Galapagos islands represent one of the best examples of this phenomenon.
Finches found on different islands of Galapagos have different types of modified beaks due to different
feeding habits, but had common ancestor. Common ancestral seed eating ground finches radiated to
different geographical areas and adapted different feeding habits, so developed different types of
beaks.

16. Human Evolution

17. Origin and Evolution of Man
◦ Human evolution, or anthropogenesis, is the part of biological evolution concerning the emergence of Homo
sapiens sapiens as a distinct species from other hominids, great apes and placental mammals. Primates called
Dryopithecus and Ramapithecus were existing about 15 mya (millions year ago). 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. These revealed hominid feature
leading to the belief that about 3-4 mya, man-like primates walked in Eastern Africa. They were not taller
than 4 feet but walked up right.
◦ Australopithecus probably lived in East African grasslands about two mya. They hunted with stone weapons
but essentially ate fruit. Some other evidences showed the presence of different creatures called the first
human-like being the hominid and was called Homo habilis. Their brain capacities were between 650-800 cc.
They probably do not eat meat.
(Continuation)

18. ◦ Fossils discovered in Java in 1891 revealed the next stage of human evolution called Homo erectus about
1.5 mya. Homo erectus had a brain capacity of around 900 cc (cubic centimeter). They probably ate meat.
◦ The Neanderthal man with a brain size of 1400 cc lived in near East and Central Asia between 1,00,000 -
40,000 years back. They used hides 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.

20. Evidences of Evolution
◦ There are five lines of evidence that support evolution: the fossil record, biogeography, comparative
anatomy, comparative embryology, and molecular biology.
❖ Fossil Evidence:
Fossils are the preserved remains or traces of animals, plants, and other organisms
from the past. Fossils are important evidence for evolution because they show that life on earth was once
different from life found on earth today.

21. ❖ Comparative Biochemistry:
Comparative biochemistry has various definitions but most common being the study of
evolutionary relationships or study of differences and similarities in biological or physiological processes
among living organisms. For evolutionary studies, comparative biochemistry employs genes, proteins and
enzymes.
❖ Comparative Anatomy:
Comparative anatomy, the comparative study of the body structures of different
species of animals in order to understand the adaptive changes they have undergone in the course of
evolution from common ancestors.
(Continuation)

22. ◦ Sometimes, structures in different species appear to be homologous, but they are not. These structures are said to be
analogous structures. Analogous structures have the same function, but do not share a common origin. Analogous
structures evolve separately in unrelated species, and their presence does not imply that the organisms descended from
the same ancestor. Because analogous structures evolved separately, their structure and arrangement are also very
different.
For example, birds have a single pair of wings that are composed mostly of muscle, bone, and feathers. Dragonflies are
invertebrates, whose two pairs of wings are made mostly of integument.
Identification of vestigial structures can also indicate a relationship between two species.
◦ Vestigial structures are non-functional remnants of features that were once operational in a distant ancestor. These
structures help establish evolutionary pathways for modern organisms. For example, the presence of vestigial pelvic
girdles and femurs in snakes and whales implies that snakes and whales descended from animals that walked on land.
Because the presence of these structures was not harmful to the organisms, there was no evolutionary pressure for the
structures to completely disappear.

23. ❖ Comparative Embryology:
Comparative embryology is the branch of embryology that compares and
contrasts embryos of different species. It is used to show how all animals are related. Many things are
compared (such as whether or not the organism has a notochord or gill arches).

24. ❖ Physiological Similarities:
Physiological evidence of evolution deals with the functions of body
parts among different species. Analogous structures are body parts of different species that have a similar
function.
❖ Biogeography:
Biogeography, the study of the geographical distribution of organisms, provides information about how and
when species may have evolved. Fossils provide evidence of long-term evolutionary changes, documenting
the past existence of species that are now extinct.

25. Phylogeny & Cladograms
➢ The key difference between cladogram and phylogenetic tree is that cladogram shows only the
relationship between different organisms with respective to a common ancestor while phylogenetic
tree shows the relationship between different organisms with respect to the evolutionary time and the
amount of change with time.

26. Speciation & Biodiversity
◦ Speciation occurs when populations of a species become so different over time that they can no longer interbreed.
Speciation results in an overall increase in the world's biodiversity.
◦ Biodiversity is the biological variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic,
species, and ecosystem level.
◦ The reason why there is still life on Earth is that extinctions are, at least on geological timescales, naturally balanced by
the formation of new species: speciation is an incessant driver of biodiversity. Stable species patterns represent a
dynamical equilibrium between extinction and speciation.

29. Time for practice questions.

30. Who proposed that the first form of life could have come from
pre-existing non-living organic molecules?
(a) S.L. Miller.
(b) Oparin and Haldane.
(c) Charles Darwin.
(d) Alfred Wallace.

31. The first life originated
(a) on land.
(b) in water.
(c) in air.
(d) all of these.

32. Fitness according to Darwin refers to
(a) number of species in a community.
(b) useful variation in population.
(c) strength of an individual.
(d) reproductive fitness of an organism.

33. Charles Darwin worked in
(a) Galapagos Island.
(b) Australian Island Continent.
(c) Malay Archipelago.
(d) none of these.

34. The theory of natural selection was given by
(a) Lamarck
(b) Alfred Wallace
(c) Charles Darwin
(d) Oparin and Haldane.

35. Industrial melanism as observed in peppered moth proves that
(a) the dark melanic form of the moth has no selective advantage
over lighter form in industrial area.
(b) the lighter-form moth has no selective advantage either in
polluted industrial area or non-polluted area.
(c) melanism is a pollution-generated feature.
(d) the true black melanic forms escaped unnoticed so they
managed to survive resulting in more population of black moths.

36. Replacement of the lighter - coloured variety of peppered moth
(Biston betularia) to its darker variety (Biston carbonaria) in
England is the example of
(a) natural selection.
(b) regeneration.
(c) genetic isolation.
(d) temporal isolation.

37. The diversity in the type of beaks of finches adapted to different
feeding habits on the Galapagos Islands, as observed by Darwin,
provides evidence for
(a) intraspecific competition.
(b) interspecific competition.
(c) origin of species by natural selection.
(d) origin of species by mutation.

38. By the statement 'survival of the fittest', Darwin meant
that
(a) the strongest of all species survives.
(b) the most intelligent of the species survives.
(c) the cleverest of the species survives.
(d) the species most adaptable to changes survives.

39. According to Lamarckism, long necked giraffes evolved
because
(a) nature selected only long necked ones.
(b) humans preferred only long necked ones.
(c) short necks suddenly changed into long necks.
(d) of stretching of necks over many generations by short necked
ones.

40. Which of the following differences between Lamarckism
and Darwinism is incorrect?
Lamarckism Darwinism
It does not consider struggle for
existence.
Struggle for existence is very important
in this theory.
Only useful variations are transferred to
the next generation.
All the acquired characters are
inherited to the next generation.
Neglects survival of the fittest. Based on survival of the fittest.
None of these
A
B
C
D

41. Darwinism explains all the following except
(a) offspring with better traits that overcome competition are best
suited for the environment.
(b) variations may or may not be inherited from parents to offspring
through genes.
(c) within each species, there are variations.
(d) organisms tend to produce more number of offspring than can
survive.

42. The primate which existed 15 mya was
(a) Homo habilis.
(b) Australopithecus.
(c) Ramapithecus.
(d) Homo erectus.

43. The extinct humans who lived 1,00,000 to 40,000 years ago,
in East and Central Asia, used hides to protect their bodies
and had brain capacity of 1400 c.c. were
(a) Homo habilis
(b) Neanderthal man
(c) Cro-Magnon man
(d) Ramapithecus.

44. Which of the following statements is correct regarding
evolution of mankind?
(a) Homo erectus is preceded by Homo habilis.
(b) Neanderthal man and Cro-Magnon man were living at the
same time.
(c) Australopithecus was living in Australia.
(d) None of these

45. The most apparent change during the evolutionary history
of Homo sapiens is traced in
(a) loss of body hair
(b) walking upright
(c) shortening of the jaws
(d) remarkable increase in the brain size.

46. Which of the following appeared during ice age between75,000-
10,000 years ago?
(a) Cro-Magnon man
(b) Neanderthal man
(c) Modern Homo sapiens
(d) Heidelberg man