Evolution is an orderly change from one form to another.

Evolutionary Biology is the study of evolutionary history of life forms.

ORIGIN OF LIFE
- Big Bang Theory states that universe originated about 20 5. Theory of chemical evolution: Proposed by Oparin &
billion years ago by a singular huge explosion. Haldane. It states that, the first form of life was originated
- The earth was formed about 4.5 billion years ago. from non-living inorganic & organic molecules such as
- There was no atmosphere on early earth. Water vapour, CH4, CH4 , NH3 , H2 O, sugars, proteins, nucleic acids etc. i.e.
CO2 & NH3 released from molten mass covered the surface. “Abiogenesis first, but biogenesis ever since”.
- The UV rays from the sun broke up water into H2 and O2 . Urey-Miller experiment
- Oxygen combined with NH3 & CH4 to form water, CO2 etc.
- Harold Urey &
- The ozone layer was formed. As it cooled, the water vapour Stanley Miller
fell as rain to form oceans. experimentally
- Life appeared almost four billion years ago.
proved theory of
THEORIES OF ORIGIN OF LIFE chemical
1. Theory of spontaneous generation (Abiogenesis): It evolution. They
states that, life came out of decaying and rotting matter created a
like straw, mud etc. condition like
Louis Pasteur demonstrated that life comes only from that of primitive
pre-existing life and disproved this theory. earth (i.e. high
He showed that in pre-sterilized flasks, life did not come temperature,
from killed yeast. In another flask open to air, new living volcanic storms,
organisms arose. reducing atmosphere with CH4 , NH3 , H2 O, H2 etc).
2. Biogenesis: Proposed by Francisco Redi, Spallanzani & - They made electric discharge in a closed flask containing
Louis Pasteur. It states that, life originates from pre- CH4 , NH3 , H2 and water vapour at 800o C. As a result, some
existing life. amino acids are formed.
3. Cosmic theory (Theory of Panspermia): It states that, - In similar experiments, others observed formation of
the units of life (spores) were transferred to different sugars, nitrogen bases, pigment and fats.
planets including earth.
First non-cellular form of life originated 3 billion years ago.
4. Theory of special creation: It states that, living & non- They were RNA, proteins, Polysaccharides etc.
living was created by some supernatural power (God).

EVIDENCES FOR EVOLUTION

1. Paleontological evidences similarity in structure and origin but different functions.
Paleontology: It is the study of fossils. This phenomenon is called Homology.
Fossils are remnants of life forms found in rocks (earth crust). - E.g. Human hand, Whale’s flippers, Bat’s wing & Cheetah’s
Fossils are written documents of evolution. foot. These forelimbs have different functions but similar
Significance of fossils: anatomical structures such as bones (e.g. humerus, radius,
a. To study phylogeny (evolutionary history or race history). ulna, carpals, metacarpals & phalanges).
E.g. Horse evolution. - Homology is also seen in heart, brain etc.
b. To study the connecting link between two groups of - Homology in plants: E.g. Thorns of Bougainvillea and
organisms. E.g. Archaeopteryx. tendrils of Cucurbita.
c. To study about extinct animals. E.g. Dinosaurs. - The origin of homologous organs is due to Divergent
d. To study about geological period by analysing fossils in evolution. It is the evolution by which related species
different sedimentary rock layers. The study showed that become less similar to survive and adapt in different
life forms varied over time and certain life forms are environmental condition.
restricted to certain geological time spans. - Homology indicates common ancestry.
2. Morphological and Anatomical evidences b. Analogous organs
Comparative anatomy and morphology shows that different These are the organs having similar function but different
forms of animals have some common structural features. This structure & origin. This phenomenon is called Analogy. E.g.
can be explained as follows: ▪ Wings of insects (formed of a thin flap of chitin) and wings
a. Homologous organs of birds (modified forelimbs).
▪ Eyes of Octopus (retina from skin) and mammals (retina
- Homologous organs are the organs having fundamental
from embryonic brain).
1
▪ Flipper of Penguins and Dolphins. 5. Embryological evidences
▪ Sweet potato (modified root) & Potato (modified stem). - Proposed by Ernst Haeckel.
▪ Trachea of insects (from ectoderm) and lungs of - He observed that all vertebrate embryos have some
vertebrates (from endoderm). common features that are absent in adult.
Origin of analogous organs is due to Convergent evolution. - E.g. all vertebrate embryos (including human) develop
It is the evolution by which unrelated species become more vestigial gill slits just behind the head. But it is functional
similar to survive and adapt in similar environmental condition. only in fish and not found in other adult vertebrates.
3. Adaptive radiation (Biogeographical evidences) - However, Karl Ernst von Baer rejected this proposal. He
noted that embryos never pass through the adult stages of
Adaptive radiation (evolution by adaptation) is the evolution
other animals.
of different species in a geographical area starting from a
point. E.g. 6. Evidences for evolution by natural selection
o Darwin’s finches Natural selection is the process by which the organisms that
in Galapagos are best suited for their environment survive and reproduce.
Islands. Some evidences are given below.
o Australian Industrial melanism:
marsupials
▪ In England, before industrialization (1850s), there were
(Marsupial
more white-winged moths (Biston betularia) on trees than
radiation).
dark winged or melanised moths (Biston carbonaria). After
o Placental mammals in Australia.
industrialization (1920), more dark-winged moths and less
When more than one adaptive radiation is appeared in an white winged moths were developed.
isolated geographical area, it results in convergent evolution. Reason:
E.g. Australian Marsupials and Placental mammals. Before industrialization: There was white lichens covered
Placental m am m als Australian Marsupials the trees. In that background, white winged moths survived
Mole Marsupial mole but dark winged moths were picked out by predators.
Ant eater Numbat (Ant eater)
After industrialization: The tree trunks became dark due
Mouse Marsupial mouse
Lemur Spotted cuscus
to industrial smoke and soot. No growth of lichens. Under
Flying squirrel Flying phalanger this condition the white winged moth did not survive
Bobcat Tasmanian tiger cat because the predators identified them easily. Dark w inged
Wolf Tasmanian w olf moth survived because of suitable dark background.
4. Biochemical evidences Natural selection by anthropogenic action:
- Organisms show similarities in proteins, genes, other ▪ It is the development of resistant varieties in organisms due
biomolecules & metabolism. It indicates common ancestry. to human action. E.g. Excess use of herbicides, pesticides,
antibiotics or drugs etc.

THEORIES OF BIOLOGICAL EVOLUTION

1. Lamarckism (Theory of Inheritance of Darwinism is based on 2 key concepts:
Acquired characters) o Branching descent: It explains that all organisms are
It is proposed by Lamarck. It states that evolution of life forms modified descendants of previous life forms.
o Natural selection: Consider a bacterial colony A growing
occurred by the inheritance of acquired characters.
on a given medium. If the medium composition is changed,
Acquired characters develop by use and disuse of organs.
only a part of the population can survive under new
o Evolution by use of organs: E.g. Long neck of giraffe is
condition. This variant population (B) outgrows the others
due to continuous elongation to forage leaves on trees. This
and appears as new species, i.e. B is better than A under
acquired character was inherited to succeeding generations.
new condition. Thus, nature selects for fitness.
o Evolution by disuse: E.g. Disappearance of limbs in snakes.
Natural selection is based on the following facts:
This theory was eliminated out because it is proved that the • Heritable minor variations: It is either beneficial or
characters are inherited only through genes. harmful to the organisms.
2. Darwinism (Theory of Natural selection) • Overproduction: Population size grows exponentially
- Proposed by Charles Darwin. due to maximum reproduction (E.g. bacterial population).
- It was based on observations during a sea voyage in a sail • Limited natural resources: Resources are not increased
ship called H.M.S. Beagle. in accordance with the population size.
- Alfred Wallace (a naturalist worked in Malay • Struggle for existence: It is the competition among
Archepelago) had also come to similar conclusions. organisms for resources so that population size is limited.
- Work of Thomas Malthus on populations influenced Darwin. • Survival of the fittest: In struggle for existence,
organisms with beneficial variations can utilize resources
2
 better. Hence, they survive and reproduce. This is called - He conducted experiments on Oenothera lamarckiana
Survival of the fittest. It leads to a change in population (evening primrose) and believed that evolution takes place
characteristics and new forms appear. through mutation and not by minor variation.
Darwin ignored about origin of variation and mechanism of - Darwinian variation is minor, slow and directional. Due
evolution or speciation. to this, gradual evolution occurs.
- Mutation is sudden, random and directionless variation.
MECHANISM OF EVOLUTION
Here, speciation is by saltation (single step, large mutation).
- Hugo de Vries proposed Mutation Theory of evolution. - Mutation is the origin of variation for evolution.

HARDY-WEINBERG PRINCIPLE
- It states that allele frequencies in a population are stable d. Genetic recombination: Reshuffling of gene combinations
and constant from generation to generation in the absence during crossing over resulting in genetic variation.
of other evolutionary influences. e. Natural selection: It is 3 types.
- The gene pool (total genes and their alleles in a population) i. Stabilizing selection: Here, more individuals acquire
remains a constant. This is called genetic equilibrium mean character value and variation is reduced. E.g.
(Hardy-Weinberg equilibrium). consider the body size of organisms.
- Sum total of all the allelic frequencies = 1
- E.g. In a diploid, p and q are the frequencies of alleles A &
a respectively.
The frequency of AA = p2
The frequency of aa = q2
The frequency of Aa = 2pq
Hence p2 + 2pq + q2 = 1 [binomial expansion of (p+q) 2 ] ii. Directional selection: Here, individuals of one
extreme are more favoured.
Change of frequency of alleles in a population causes
disturbance in genetic equilibrium. This is due to evolution.
Factors affecting Hardy-Weinberg equilibrium
a. Gene migration: Gene flow from one population to another.
Here gene frequencies change in both populations. Gene
flow occurs if migration happens multiple times.
iii. Disruptive selection: Here, individuals of both
b. Genetic drift: The accidental gene flow causing change
extremes are more favoured.
in frequency. Sometimes, the change in 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.
c. Mutation: Mutations result in formation of new
phenotypes. Over few generations, this leads to speciation.

A BRIEF ACCOUNT OF EVOLUTION

The geological time scale includes 4 eras: Proterozoic, In 1938, a Coelacanth fish (lobefins) was caught in South
Palaeozoic, Mesozoic & Cenozoic. Africa which was thought to be extinct. This fish was
1. Proterozoic era: 2500 - 541 million yrs ago (mya) evolved into first amphibians (ancestors of modern day
frogs and salamanders).
- First cellular forms of life appeared (2000 mya).
- 320 mya: Sea weeds and few plants were existed.
- Some of the cells had the ability to release O 2 as the light
- Amphibians evolved to reptiles. They lay thick-shelled eggs
reaction in photosynthesis.
(do not dry up in sun).
- Single celled organisms became multicellular organisms.
- Giant ferns (Pteridophytes) were present but they all fell
2. Palaeozoic era (540 - 252 mya) to form coal deposits slowly.
- It has 6 periods: Cambrian (540 - 490 mya), Ordovician 3. Mesozoic era (252 - 66 mya) – Age of reptiles
(490 - 443 mya), Silurian (425 mya), Devonian (405 mya), - It has 3 periods: Triassic (230 mya), Jurassic (208 mya) &
Carboniferous (360 mya) & Permian (285 mya).
Cretaceous (144 mya).
- 500 mya: Invertebrates were formed. - 200 mya: Some of the land reptiles went back into water to
- 450 mya: First land organisms (plants) appeared.
evolve into fish-like reptiles (E.g. Ichthyosaurs).
- 400 mya: Arthropods invaded the land.
- The land reptiles were dinosaurs (Tyrannosaurus rex,
- 350 mya: Jawless fishes were evolved. Fishes with stout Triceratops, Pteranodon, Stegosaurus, Brachiosaurus etc.)
and strong fins could move on land and go back to water.

3
 T. rex was the largest dinosaur (20 feet in height, huge Hairy. Walked like gorillas & chimpanzee.
fearsome dagger-like teeth). Dryopithecus: ape-like.
- First toothed birds were emerged. Ramapithecus: man-like.
4. Cenozoic era (66 - 0 mya) • 3-4 mya: Man-like primates. Height up to 4 feet. Fossils
- Age of Mammals & Angiosperms. of man-like bones found in Ethiopia & Tanzania.
- It has 2 periods: Tertiary (66 mya) & Quaternary (2 mya • 2 mya: Australopithecus. Lived in East African grass
- Age of man). lands. Hunted with stone weapons. Ate fruits.
- 65 mya: Dinosaurs suddenly disappeared. Some say Homo habilis: First human-like being (hominid).
climatic changes killed them. Some say most of them Brain capacity: 650-800 cc. Did not eat meat.
evolved into birds. • 1.5 mya: Homo erectus (Java man). Large brain (900 cc).
- First mammals were shrew-like. Their fossils are small sized. Ate meat.
• 1 lakh - 40,000 yrs ago: Homo neanderthalensis
- In South America, there were mammals resembling horse,
hippopotamus, bear, rabbit etc. Due to continental drift, when (Neanderthal man).
South America joined North America, these animals were Brain capacity: 1400 cc. Lived in East & Central Asia. Used
overridden by North American fauna. hides to protect their body. Buried their dead.
- Due to continental drift, Australian marsupials survived • 75,000 - 10,000 yrs ago (ice age): Homo sapiens (Modern
because of lack of competition from any other mammals. man).
Pre-historic cave art developed about 18,000 years ago.
ORIGIN AND EVOLUTION OF MAN
Agriculture & settlements: 10,000 years ago.
• 15 mya: Dryopithecus & Ramapithecus.

Visit: www.bankofbiology.com
MODEL QUESTIONS
1. Match the following:
A B C
Charles Darwin Chemical evolution Use and disuse of organs
Lamarck Natural selection Abiogenic origin of life in ocean
Hugo de Vries Biogenesis Oenothera lamarckiana
Louis Pasteur Inheritance of acquired characters Survival of the fittest
Oparin & Haldane Mutation Disproved theory of spontaneous generation
2. Analyze the relationship between first two words and fill the fourth place.
a. Homology: Divergent evolution Analogy: ………………..
b. Pisum sativum: Mendel Oenothera lamarckiana: ………………
3. Classify the following points into two categories. Give suitable titles.
Random & directionless, Minor variation, Gradual evolution, Slow & directional,
Large variation, Speciation by saltation
4. A bacterial infection was effectively controlled by using a specific antibiotic for a long time. But now- a- days this
antibiotic is not found to be so effective. Give a scientific explanation for this phenomenon based on evolution.
5. Hardy- Weinberg Principle has a great contribution in population genetics.
a. State Hardy- Weinberg Principle. b. What are the factors affecting genetic equilibrium?
c. What is meant by Founder effect?
6. Select the correct order
a. Paleozoic era → Proterozoic era → Mesozoic era → Coenozoic era
b. Mesozoic era → Proterozoic era → Coenozoic era → Paleozoic era
c. Proterozoic era → Paleozoic era → Mesozoic era → Coenozoic era
d. Coenozoic era → Paleozoic era → Mesozoic era → Proterozoic era
7. Prepare a flowchart showing the evolution of man.