Best Notes for CHP 7 evolution

1. EVOLUTION
ARCHANA KUMARI
PGT BIO

2. • Evolutionary biology is the study of history
life forms on the Earth.
• To understand the evolution in flora and
fauna over a period of millions of years on
the earth, we must understand the origin of
life beginning with the evolution of the earth,
of stars, and the universe itself.
• Origin of life is believed to be a unique event
in the history of universe.
• The Big Bang Theory attempts to explain to us
the origin of universe

3. •
Origin- point or place where something begins,
arises, or is derived
Evolution- the process by which different kinds
of living organism are believed to have
developed from earlier forms during the
history of the earth
But the term evolution has wider perspectives.

5. The Big Bang theory
• A singular huge explosion of very dense matter from
a point of singularity.
• This caused the universe to expand and the
temperature to fall drastically.
• After some time hydrogen and helium were formed.
• The gases condensed due to gravitation. They later
formed the galaxies in the universe. The Earth is
believed to have been formed about 4.5 billion
years back in the solar system of the Milky Way
galaxy.

6. Condition of early earth:
• The Earth formed 4.5 billion years back.
• There was no atmosphere on early earth.
• Water vapor, methane, carbon dioxide and ammonia released from
molten mass covered the surface.
The UV rays from the sun caused decomposition of water into
hydrogen and oxygen. Hydrogen gas being lighter escaped into
space.
• Oxygen that remained behind combined with ammonia and
methane to form water, CO2 and other compounds.
• The ozone layer was formed.
• As the water vapor cooled, it fell as rain, to fill all the depressions
and form oceans.
• Life appeared around 500 Million years after the earth was formed.

7. • Universe – 20 billion years old
• Before the big bang, scientists believe, the entire vastness
of the observable universe, including all of its matter and
radiation, was compressed into a hot, dense mass
• Before 10-20 billion years probably 13.8 billion years ago
Big explosion
• Universe expanded ; Temperature came down; Hydrogen
and helium formed; Gases condensed and galaxies formed

15. Origin of Life (theories):
1.Theory of spontaneous Generation
(Theory of Abiogenesis):-
• For a long time it was also believed that life
could originate from decaying and rotting
matter like straw, mud etc

17. Louis Pasteur experiment:
disproved the theory of spontaneous generation.
• Careful experimentation demonstrated that
life comes only from pre-existing life.
• He showed that in flasks that were sterilized
prior to the experiment, life did not originate
from killed yeast.
• At the same time, if a similar flask was left
open to air, new living organism arose from
“killed yeast”.

18. Louis Pasteur demonstrated that life comes only from
pre-existing life.
However, it did not answer how the first life
form came on earth.

19. 2.Theory of Biogenesis:-
• Spontaneous generation was replaced by the
theory of biogenesis in the 19th century.
• The theory of biogenesis states that only living
organisms can produce other living organisms.

20. 3.Cosmic Theory or Theory of s
Panspermia
• Early Greek believed that units of life called
spores were brought to different planets
including earth.
• This theory is called as Panspermia and is still
a favored by many astronomers.
• Life originated after 0.5 billion years.
i.e. 4 billion years ago

22. 4.Theory of Special creation:
• This theory says that all living organisms
were created by some supernatural power
(God). God created the first man Adam.

23. Theory of Chemical Evolution
• Oparin – Haldane theory of origin of life:
• proposed that the first forms of life originated from pre-
existing nonliving organic molecules (e.g. RNA, protein
etc.).
• Formation of life was preceded by chemical evolution
i.e. formation of diverse organic molecule from
inorganic constituents.
• In 1953, S.L. Miller, an American scientist demonstrated
the same experimentally in a laboratory scale

24. In 1953, S.L. Miller, an American scientist
created early earth condition in lab
• In 1953 S.L.Miller an American scientist
created similar conditions in laboratory scale.
• To simulate conditions of primitive earth he
created electric discharge in a closed flask.
• This raised the temperature up to 8000C.
• Used CH4, H2, NH3 and water vapor inside
the flask.
• He observed the formation of amino acids

26. Urey and Miller Experiment:
• The Conditions of the Earth were –
• High Temperature.
• Volcanic Storms.
• Reducing atmosphere containing CH4, NH3
etc.

27. Early Earth like situation created in Lab
• high temperature,
volcanic storms,
reducing atmosphere
containing CH4, NH3
• electric discharge in a
closed flask containing
CH4, H2, NH3 and
water vapour at 800 C
Formation of Amino
Acids
(Others observed
other
organic
biomolecules)

28. 3 million years back - first non-cellular forms of life
(RNA, Protein, Polysaccharide etc)
• 2 million years ago- first cellular form- Unicellular- in
water
• biogenesis- the first form of life arose slowly
through evolutionary forces from non-living
molecules is accepted by majority

29. Acceptance of chemical evolution
theory: (evidences):
• Miller observed the synthesis of amino acids from
simple inorganic chemicals. He did this by
recreating the conditions that were believed to
exist on primitive earth in the laboratory.
• In similar experiments formation of sugars,
nitrogen bases, pigment and fats were also
observed by other scientists.
• Analysis of meteorite content showed the
presence of similar compounds. This indicates
that similar processes are occurring elsewhere in
space.

30. Theory of Origin of Species by Natural
Selection:-
• In observations made during a sea voyage in a sail
ship called H.M.S. Beagle round the world,
Charles Darwin concluded that existing life forms
share similarities to varying degrees not only
among themselves but also with life forms that
millions of years ago.
• Many such life forms don’t exist anymore. Due to
various reasons there have been extinctions of
different life forms in the past. There also have
been the emerg

31. There has been gradual evolution of
life forms
• All populations of organisms have variations in
characteristics.
• Individuals with characteristics that allow better
adaptability survive better in natural conditions
(climate, food, physical factors, etc.) and would
therefore outbreed others with less favorable
characteristics.
• This ensures that the survival of the variety that is most
adaptable to change.
• It leads to the survival and propagation of the fittest
organisms in the population as it can survive and
outlast change.

32. Survival of the fittest:
• The fitness according to Darwin refers ultimately to
the ability to survive a change. Therefore only the
fittest organisms survive and produce more progeny
then others.
• These, therefore, have better survival capacities and
hence are selected by nature. He called it as natural
selection.
• Alfred Wallace, a naturalist who worked in Malay
Archipelago had also come to similar conclusions
around the same time.
• The geological history of earth is closely related to the
biological history of earth.

34. Theory of special creation
Vs
Theory of evolution
special creation
• all living organisms were
created as such
• diversity was always the
same since creation
• earth is about 4000 years
old
evolution
• living forms share
similarities among
themselves and with forms
that existed millions of
years ago
• There had been extinctions
• new forms of life arose at
different periods
• Earth is billions of years old

35. Lamarckism
• Use and disuse theory
• Inheritance of acquired character

36. DARWINISM
•Prodigality of
species
•Struggle for
existence
•Variation
•Descent with
modification
•Natural selection
Alfred Wallace

37. WHAT ARE EVIDENCES FOR
EVOLUTION?
1.Paleontological evidence:
• Fossils are remains of hard parts of life-forms found in rocks.
• Different-aged rock sediments contain fossils of different life-forms
who probably died during the formation of the particular
sediment.
• They represent the extinct organisms (e.g. Dinosaurs).
• A study of different sedimentary layers in which fossils were
present 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 span.
• Hence new forms of life are believed to have originated at
different times in the history of earth.
• All this called Paleontological evidence.

38. Fossil evidences

39. Comparative anatomy and
morphological evidence:
• Comparative anatomy and morphology shows
similarities and differences among organisms
of today and those that existed years ago.
Homology indicates common ancestry.
• Other examples of homologous organ are
vertebrate hearts and brains.
• Thorn of Bougainvillea and tendrils of
Cucurbita represent homology

42. Divergent evolution:
• Different mammals like bats, whales, cheetah and humans
share similarities in the pattern of bones of forelimbs.
• These forelimbs perform different functions in these
animals but they have similar anatomical structure – all of
them have humerus, radius, ulna, carpals, metacarpals
and phalanges in their forelimbs. Thus it can be seen that
the same structure developed along different directions
due to adaptation to different needs.
• This direction of evolution is called as divergent evolution
and these structures are homologous to each other.

43. Convergent evolution:
• Wings of butterfly and of birds both appear similar.
• Anatomically they do not have similar structure though
they perform similar function.
• Hence analogous structures are a result of convergent
evolution.
• Eyes of different organisms like that of octopus of
mammals.
• Flippers of Penguins and Dolphins.
• Sweet potato (root modification) and potato (stem
modification) for storage of food

45. Morphological and Anatomical
evidences
Homologous organs-
• Same structure evolved in
different direction
• Divergent evolution
Analogous organs-
• different structures
evolving for the same
function
• Convergent evolution

46. Homologous organs-
Both Venus flytrap and Pitcher plants have modified
their leaves to catch insects and digest them as food.
The plant poinsettia has modified its leaves which are
bright red to look like the petals of a flower.
The thorns of a pomegranate and the tendrils of a
passion fruit share common homology arising from an
axillary bud but they are structurally and functionally
different.
The cactus has modified its leaves into small spines to
reduce water loss in arid climates with high
temperatures and to protect itself from roving
herbivores.

47. Embryological evidences

48. Embryological evidences
• • Ernst Heckel proposed this evidence as evolution based
on observation of certain common features during
embryonic stage of all vertebrates but are absent in adult.
• All vertebrate embryos including human embryo develop a
row of vestigial gill slits just behind the head. It is seen that
it is a functional organ only in fish. Gills are not found in any
other adult vertebrates.
• The embryological evidence was disregarded and disproved
by Karl Ernst von Baer on the basis of careful study
performed by him.
He noted that the similarities in embryos never pass through
the adult stages of other animals.

49. Biochemical evidences
• Similarities in proteins and genes performing
a specific function among different organisms
give clues regarding common ancestry.

50. Darwin’s Finches

51. ADAPTIVE RADIATION
• Darwin’s Finches
• evolution of different species in a given
geographical area starting from a point and
literally radiating to other areas of habitats is
called adaptive radiation
• more than one adaptive radiation in an isolated
geographical area (representing different
habitats), can be a convergent evolution
• Example for such adaptive radiations - Placental
mammals and Australian marsupials

52. Australian marsupial:

53. In Australia it was seen that a number of marsupials
had evolved from an ancestral stock.
• These marsupials were all different from each other.
• • When more than one adaptive radiation appears to
have occurred in an isolated geographical area
(representing different habitats), it can be called as
convergent evolution.
• Placental mammals in Australia were also seen to
exhibit adaptive radiation.
• They seem to be evolved from a marsupial into various
placental mammals.
• The placental mammals are showed similarities to the
ancestral marsupial (e.g. placental wolf and Tasmanian
wolf-marsupial).

55. Biological evolution
• Evolution by natural selection started when
cellular forms of life with differences in
metabolic capability originated
• Rate of appearance of new forms is linked to
the life cycle or the life span
• In bacteria new forms may arise within days,
in higher organisms millions of years
• Fittest variation (better adaptation) is
inherited

56. Story of the world concerned - Evolution
is a process
• Story of the life on earth concerned-
Evolution is result of a process namely
natural selection
• Population studies which aided Darwin
• Populations are stable, members vary in
characters, many variations are inherited,
resources are limited theoretically grow
exponentially but limited in reality

57. Mechanism of evolution
Darwin
• minor variations (heritable)
important for evolution
• variations are small and
directional
• Evolution was gradual
Hugo de Vries
• Mutation causes evolution
• Mutations are random and
directionless
• mutation caused speciation
and known as saltation

58. Hardy-Weinberg Principle
• Before learning Hardy Weinberg Law certain
fundamentals from genetics are essential
• Allele is one of a number of alternative forms
of the same gene or same genetic locus

59. • Gene frequency or Allele frequency : is the
proportion of a particular allele among all alleles
of a character. i.e. Number of copies of a
particular allele divided by the number of copies
of all alleles
(Proportion of dominant allele A or recessive allele a)
• Genotype frequency in a population is the
number of individuals with a given genotype
divided by the total number of individuals in the
population
(AA/total or Aa/total or aa/total)

60. Numerical example
• 100 plants are studied
• 49 red-flowered plants with the genotype AA
• 42 pink-flowered plants with genotype Aa
• 9 white-flowered plants with genotype aa
• homozygous individuals have two copies of an allele
• heterozygotes have only one
• allele frequency for a

61. • the genotype frequency of aa homozygotes

62. Hardy Weinberg principle says that allele
frequencies in a population are stable and is
constant from generation to generation. This
is called genetic equilibrium.
Sum total of all the allelic frequencies is 1.
Individual frequencies, for example, can be named p, q,
etc.
In a diploid, p and q represent the frequency of allele A
and allele a.
If the allele A frequency is denoted by the symbol p and
the allele a frequency denoted by q, then p+q=1.

63. • The expected genotype frequencies are f(AA) = p2 for
the AA homozygotes, f(aa) = q2 for the aa
homozygotes, and f(Aa) = 2pq for the heterozygotes.
The genotype proportions p2, 2pq, and q2 are called the
Hardy–Weinberg proportions
• the sum of all genotype frequencies (p2 + 2pq + q2 ) of
this case is the binomial expansion of the square of the
sum of p and q i.e. (p+q) 2
• When p+q=1,
• (p+q) 2=12=1 and its binominal expansion
p2 + 2pq + q2=1

64. • Therefore (p + q)2 = p2 + 2pq + q2 = 1. A solution of
this equation is q = 1 − p. (When p+q=1, q = 1 − p)
• The two conclusion of the Hardy-Weinberg Law can
be mathematically demonstrated
P q
P p2 qp
q qp q2
1) genotypic frequencies for AA is p^2, the genotypic
frequency for Aa is 2pq and the genotypic
frequency for aa will be q^2. These are the values
that are predicted by the law.

65. 2) second prediction is that the frequencies of
the two alleles will remain the same
p = f(AA) + ½f(Aa) (substitute from the above
table)
p = p2 + ½(2pq) (factor out p and divide)
Therefore p = p2 + pq
p = p(p + q) (p + q =1; therefore q =1 - p; make
this substitution)
p = p [p + (1 - p)] (subtract and multiply) p = p

66. Results of random union of the gametes produced by an entire
population with a gene pool containing 80% A and 20% a.
0.8 A 0.2a
0.8 A 0.64 AA 0.16 Aa
0.2a 0.16 aA 0.04aa
80% of all the gametes in the population carry a dominant allele for black coat (A)
and 20% carry the recessive allele for gray coat (a).
Random union of these gametes (right table) will produce a generation:
64% homozygous for AA (0.8 x 0.8 = 0.64)
32% Aa heterozygotes (0.8 x 0.2 x 2 = 0.32)
4% homozygous (aa) for gray coat (0.2 x 0.2 = 0.04)
So 96% of this generation will have black coats; only 4% gray coats.
However, 80% (0.64 + .5*0.32) of the pool of gametes formed by this generation
with contain A
20% (0.04 + .5*0.32) of the gametes will contain a

67. • 1. mutation is not occurring
• 2. natural selection is not occurring
• 3. the population is infinitely large
• 4. all members of the population breed
• 5. all mating is totally random
• 6. everyone produces the same number of
offspring
• 7. there is no migration in or out of the
population

68. Factors affecting Hardy-Weinberg
equlibrium
• gene migration or gene flow,
• genetic drift,
• mutation,
• geneticrecombination and
• natural selection

70. • Multi cellular- Invertebrates 500 mya
• Jawless fish- 350 mya
• Fish to land- 350 mya
• Sea weeds and few plants- 320 mya
• Reptiles domination- 150 mya
• Extinction of Dinosaurs- 65 mya
• Then mammals era started

71. ORIGIN AND EVOLUTION OF MAN
• 15 mya- primates Dryopithecus and
Ramapithecus(man like) - hairy and walked
like gorillas and chimpanzees
• Ethiopia and Tanzania – fossils- 3-4 mya man-
like primates walked in eastern Africa- 4ft
walked upright
• 2mya- Australopithecines-East African
grasslands- hunted with stone weapons but
essentially ate fruit

72. • Homo habilis.The brain capacities were between
650-800cc. They probably did not eat meat.
• 1.5mya- Homo erectus had a large brain around
900cc- probably ate meat.
• 1,00,000-40,000 years back Neanderthal man
with a brain size of 1400cc lived in near east and
central Asia -hides to protect their body and
buried their dead

73. • Homo sapiens arose in Africa and moved
across continents and developed into distinct
races
• between 75,000-10,000 years ago- modern
Homo sapiens arose