Saturday 30 January 2021

Chapter 7 Evolution







Students, in the topic we will study history of life forms on earth. Changes

occurred over millions of years on earth. To acknowledge this,understanding of ‘Origin of Life’, evolution of earth, evolution of stars and origin of the universe in necessary.


Definition of Evolution: Evolution is the study of different forms of life, its

characteristics and the changes over several generations. It is the scientific theory

used by biologist to study the genetic variation in a population.


What is life: Life is an inherent capacity that an organism possesses to maintain

and reproduce itself.


Our Universe

There are several theories regarding the origin of universe but the most

accepted theory is BIG-BANG THEORY.




This Theory was proposed by Abbe Lemaitre in 1931. According to big bang theory about 15 billion years ago (but according to NCERT book its almost 20 billion years ago).


Cosmic matter is in condense from.


A fiery explosion take place which broke the condensed matter and scattered its fragments into space at an enormous velocity making a "big bang" sound and thus the theory came to known as big bang theory.


Immediately after the explosion the universe expanded rapidly from a size of a pin to about 2000 time the size of sun and hence the temperature came down. Hydrogen and Helium formed later.


The gases condensed under gravitation and formed the galaxies of the present-day universe.


Milky Way or Akash Ganga visible in the sky during night is a galaxy.



The Nebular Hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the solar system. It suggests the solar system is formed from gas and dust orbiting the sun.


Nebular hypothesis was first proposed by in 1755.


According to this hypothesis our solar system was probably created about 4.5 to 5 billion years ago when the gaseous cloud called solar nebula was formed.


As a cloud condensed, the central mass formed the Sun and the peripheral celestial bodies form planets, satellites, asteroid, meteors and comets formed the solar system.


Our Earth is located in the Milky Way or Akash Ganga Galaxy.



Earth was supposed to have been formed about 4.5 billion years back.


There was no atmosphere on early earth. Water Vapours, Methane, Carbon Dioxide and ammonia released from molten mass covered the surface.


The UV rays from the sun broke up water into hydrogen and oxygen and the lighter H2 escaped.


Oxygen combined with ammonia and methane to form water, carbon dioxide and others. The Ozone layer was formed.


As it cooled the water vapour fell as rain to fill all depressions and form oceans life appeared 500 million years after the formation of earth i.e.,almost 4 billion years back.





(i) Multiple Choice Questions:

1.Life papered.........years after the formation of earth.

(a) 100 million

(b) 1000 million

(c) 500 million

(d) 10 million


2. The earth was supposed to have been formed about......years back

(a) 4.5 billion

(b) 3.5 billion

(c) 5.5 billion

(d) none of these


3. Howold is universe?

(a) 20 billion years

(b) 10 billion years

(c) 18 billion years

(d) 5 billion years


4. Which one of the following gas was not present in the primitive atmosphere of the earth?

(a) Methane

(b) Hydrogen

(c) water vapors

(d) oxygen


5. Primitive atmosphere was made up of the mixture of :-

(a) oxygen, ammonia, methane, Water

(b) Hydrogen, ammonia, methane, oxygen

(c) oxygen, methane, water, nickel

(d) none of these


(ii) True/ False:

(a) Big-Bang theory was proposed by Abbe Lemaitre.

(b) Primitive atmosphere was an oxidizing atmosphere.


(iii). Fill ups:

(a) ............ gas was absent in the atmosphere of primitive earth.

(b) Our earth belongs to............galaxy.



(i) Multiple Choice Questions:


1. (c) 500 Million - when the earth cooled down the water vapors fell as rain to fill all depression and form the oceans life appeared.


2. (a) 4.5 billion

3. (a) 20 billion years


4. (d) oxygen - Because the primitive atmosphere was reducing (without free oxygen).


5. (d) none of these - Water vapours, methane, carbon dioxide and ammonia, released from molten mass covered the surface in primitive atmosphere.


(ii) True/ False

a. True

b. False - Because it was free of oxygen so it was reducing atmosphere.


(iil) Fill Ups

a. Oxygen

b. Milky Way or Akash Ganga


1. Define evolution?

2. Differentiate between primitive and recent atmosphere of the earth.


1. Explain the formation of Solar System.





Hello students, in the previous topic of chapter Evolution, you have learnt

about changes on early earth and conditions for origin of life. Now in today’s topic, we will discuss various theories proposed by various biologists in several periods; some of the important theories of origin of life are listed as follows.


THEORY OF SPECIAL CREATION —This theory states that entire universe was formed by super natural power, God.


It was proposed by Hebrew et. al.


God created the entire universe in

six days, according to Christianity. Adam was the first man and the first woman was Eve.


God Brahma created life in a single

stroke, according to Hindu mythology.


The first man was Manu and Shradha was the first woman.


Due to lack of scientific explanations, this theory was rejected.



It was proposed by Von Helmont (1577-1644) and states that life originated abiogenetically from non-living decaying matter like straw, mud etc. by

spontaneous generation about 3.5 billon years ago.


According to this theory, the origin of insects took place from dew, frogs and toads from muddy bottom of ponds, maggots from decaying meat,tapeworms from excreta of animals and micro-organisms from air or water.


Francisco Redi (1668), Louis Pasteur (1864) and Spallanzani (1765) rejected the abiogenesis concept experimentally.



It states that life arise from pre-existing life only.


The idea of spontaneous generation came to an end with following experiments performed by various scientists:


1. Redi’s Experiment — Francisco Redi (1668), an Italian physician, took the boiled flesh and placed it in three jars of which, one was uncovered, the second was covered’ with

parchment and third one was covered with fine muslin. He kept these jars for few days and

observed that maggots developed only in uncovered jar.Redi concluded, on the basis of

the aforementioned experiment,that life can only derive from pre-existing life, not from non-living substances.


2. Pasteur's Experiment — Louis Pasteur (1864) showed that minute organisms like protists and bacteria arise from pre-existing organisms of same kind. He took flask. Almost half filled with sugar and yeast. By heating he gave s-shaped structure to its neck.

The contents of swan necked flask were boiled to kill all the micro-organisms and tube was sealed. But when neck of flask was broken,micro-organisms appeared.

Hence, Louis Pasteur concluded that the life can arise only from pre-existing life.


3. Spallanzani’s experiments — Lazaaro Spallanzani (Italy) put hay infusion

in eight bottles and then it was boiled to make them sterile. He kept four bottles airtight and four of them loosely

corked. After few days,dense growth of micro-organisms was found in loosely corked

bottles whereas no organisms were found

to develop in airtight bottles.It was concluded that air consisted of micro-organism and was the source of contamination.



It was proposed by Ritcher (1865).


According to this theory


‘Protoplasm’ reached the earth in the form of spores or some other particles from some unknown part of universe with cosmic dust and

subsequently evolved into various

forms of life


But this hypothesis is unable to understand why  panspermia,including high temperatures and many harmful radiations, could survive in

adverse conditions on earth at that time.




Scientists now accept that it is not possible to create life spontaneously.


Specific requirements for life's appearance are essential.


T.H. Huxley and John Tyndall asserted that inorganic chemicals could produce life.


But as the knowledge of biochemistry was not available that time, their ideas were vagued.


This idea was proposed by the Russian biochemist A.l. Oparin(1923) and with J.B.S. Haldane’s assistance.


In his book “The Origin of Life on Earth” in1936, Oparin offered an extensive description of the origin of life by evolution or chemicals.


It is, thus, often called the Oparin and Haldane theory.


According to this theory, through a series of chemical reactions around 4.2 billion years ago, life emerged in water on primitive earth from chemicals,thus called the biochemical theory of origin of life.


Itis often referred to as the Modern synthetic theory of origin of life.


Evidences in support of origin of life: Miller-Urey experiment In 1953, Stanley Miller and Harold Urey conducted an experiment to test the biochemical origin of life hypothesis offered by Oparin and Haldane. Miller- Urey Experiment:


4 Miller constructed an apparatus of glass tube and flask termed as the spark discharge apparatus.


The apparatus depicted primitive earth — conditions,including a reducing atmosphere and an ocean.


A mixture of gases methane,ammonia and hydrogen was maintained in the gas chamber

in the ratio 2:2:1 and water in another chamber.


The gas mixture was pumped through the apparatus and the energy was supplied through

the use of electrodes in the gas chamber by boiling water and electric sparks.


The experiment initiated with switching on the electric source and boiling the water and is continued for a week.Observation:


4 They noticed a condensed liquid with a dark colour.


4 It was gathered and chromatographically analyzed, and the liquid was found to be a mixture of sugars, amino acids (glycine, analine, etc.) and fatty acids.



4 The experimental results support the Oparin-Haldane theory of the

origin of life that organic molecules are created from inorganic

molecules during the course of the origin of life.




(i) Multiple Choice Questions:


1. Who proposed autogenesis?

(a) Kettle-well

(b) Von Helmont

(c) Both a and b

(d) None of these


2. According to theory of special creation who formed organisms on our Planet?

(a) God

(b) Man

(c) Solar System

(d) None of these.


3. According to cosmozoic theory, life on earth came from?

(a) Ocean

(b) Rocks

(c) Space

(d) seeds




4. Who wrote the Book ‘The Origin of life on Earth’?

(a) Oparin

(b) Redi

(c) Pasture

(d) None of these


5. Primitive Atmosphere on earth was:

(a) Oxidized

(b) Reducing

(c) Dry

(d) None of these


(ii) True/ False:

1. Francesco Redi took the flesh and cooked it so that no organisms were left dead.

2. Louis Pasteur took flask filled with sugar and yeast.

3. Spore theory was proposed by Richter.


(iii) Fill ups:

1. Louis Pasteur gave.........................structure to his flasks by heating.

2. Accoring to Oparin-Halden Theory, life originated in ...................from

inorganic molecules.





A) Multiple Choice Questions:


1. (b) Von Helmont , states that life originated abiogenetically from non-living

decaying matter like straw, mud etc.


2. (a) God. This theory states that entire universe was formed by super natural

power, God.


3. (c) Space According to this theory ‘Protoplasm’ reached the earth in the

form of spores from some other part of universe.


4. (a) Oparin


5. (b) Reducing, reducing atmosphere lack oxygen. It includes CO2, H20,NH3, CHa and Ho.


B) True/ False:

1) False — Organisms were left alive

2) False - Half filled flasks with sugar and yeast

3) True


C) Fill Ups:

1) S-Shaped

2) Water



1. What is spore theory for origin of life?

2. What is the concept of Biogenesis theory?

3. Write the names of different theories for origin of life?



1. Explain Louis Pasteur's Experiment with the help of diagram.





Dear students, Origin of life has always amused human mind. Scientists have

worked for centuries to find the answer. The universe is very vast and very old —

almost 20 billion years old. Huge clusters of galaxies make this universe. Galaxies

contain stars and clouds of gas and dust.

Earth is just a smail peck in this vast universe. BIG BANG theory explains the

origin of universe -


1) It explains that singular huge explosion expanded the universe. After the

expansion, the temperature came down.


2) The conditions on the primitive earth were different from today i.e. high temperature, volcanoes, reducing atmosphere containing METHANE, AMMONIA etc. There was no free oxygen in primitive Atmosphere.


3) Large sized water bodies were formed as the earth surface cooled down; water

vapours condensed and came to surface of earth in the form of rain water. It led to

formation of oceans.


4) As the surface of earth cooled to 50

- 60°C , minerals and molecules present in water bodies combined to form simple organic compounds (like alcohols, aldehydes, glycerol, simple sugars, fatty acids,amino

acids,nitrogen bases etc) in the water

bodies.Then, complex organic compounds (like polysaccharide,fats,nucleotides, nucleic acids ) were formed from these simple organic



5) The main sources of energy for chemical reactions were:- electrical discharges, lightning, solar energy, ATP etc.


6) Non cellular prebiotic aggregates (Protobionts) were formed from complex

organic compounds. These would have RNA, protein, polysaccharides etc. These

could not reproduce but had power of growth and division. These were known as Coacervates or Microspheres.


7) Gradually, these aggregates got surrounded by complex system of enzymes which formed cytoplasm. These enzymes combined nitrogen bases, sugars and phosphates into Nucleotides. Thus, Nucleic acids were formed. The first cells used RNA as hereditary material and later evolved DNA from RNA template. Finally DNA replaced RNA as genetic material for the most organisms.


8) The first cell like structures (called EOBIONTS or PRE-CELLS) were formed in

water bodies. These were similar to mycoplasma which gave rise to monerans and

protistans. The Monerans include prokaryotes (bacteria and cyanobacteria) and

protistans gave rise to eukaryotes.



Early Greek thinkers believed units of life were spores. These units were transferred from outer space to earth. Panspermia was also advocated by astronomers.


Then came the theory of spontaneous generation. It was believed that life

came out of decaying and rotting matter like straw and mud etc.


Louis Pasteur demonstrated that life comes from pre-existing life. He sterilised flasks and showed that life did not come from killed yeast. New living organism grows in the flask that was open to air.


With this, the idea of spontaneous generation was dismissed for always but the question still existed —

Scientists were working across the world to explore the truth. Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules.



1. In 1953, Stanley L. Miller and Harold C. Urey proved experimentally formation of complex organic compounds from simple compounds under reducing conditions.


2. The apparatus had a spark chamber with two electrodes providing 75000 volts of energy, flask for boiling to temperature of 800 °C and a condenser.


3. Miller used a mixture of methane, ammonia, hydrogen and water vapours.The mixture was exposed to electric discharges followed by condensation and boiling .It was continued for 18 days.


4. Miller was able to identify 15 amino acids (like alanine, glycine,aspartic acid

etc.) , Organic acids (like lactic acid, succinic acid,acetic acid etc.) ,Ribose

sugar , purine adenine. In similar experiments other scientists also reported

formation of sugars, nitrogen bases, pigments, fats, peptides and organic acids.

5. They noticed a condensed liquid with a dark colour. It was gathered and

chromatographically analyzed, and the liquid was found to be a mixture of sugars, amino acids (glycine, analine, etc.) and fatty acids.


5. The experimental results support the Oparin-Haldane theory of the origin

of life that organic molecules are created from inorganic molecules during

the course of the origin of life.


A. Multiple Choice Questions:


Q1. The experiment that simulated conditions thought to be present on the early earth:

(a)Hersley and Chase

(b) Miller and Urey

(c) Darwin and Wallace

(d) Beadle and Tatum


Q2. Under certain conditions, scientists have obtained cell like structures. These were known as:

(a) Coacervates

(b) Monerans

(c) Protists

(d) Algae


Q3. The primitive earth's atmosphere did not contain:

(a) Hydrogen

(b) Nitrogen

(c) Oxygen

(d) water vapours




Q4. Who proposed that primitive life was formed from non living organic compounds ?

(a) Watson and Crick

(b) Oparin and Haldane

(c) Schleiden and Schwann

(d) None of these


Q5.What was not found in mixture used in Miller and Urey experiment ?

(a) Methane

(b) Ammonia

(c) Carbon dioxide

(d) water vapours


B. True and False statements:

1. RNA is genetic material in the most of the organisms

2. The primitive life was originated in water bodies.

3. Simple organic compounds were formed from complex organic compounds under reducing conditions in Miller and Urey experiment.


C. Fill in the blanks:

(A) .........eseeeee COUld Not reproduce but had power of growth and division.


(b) The primitive earth's atmosphere was .............. because of absence of


(C) voce ANG ee amino acids were found by Miller used and his experiment.



A. Multiple Choice Questions:

A1. (b) Miller and Urey

A2. (a) Coacervates

A3. (c) Oxygen

A4. (b) Oparin and Haldane

A5. (c) Carbon dioxide


B. True and False Statements:

1. False (DNA is genetic material in the most of the organisms.

2. True

3. False ( Complex organic compounds were formed from simple organic compounds under reducing conditions in Miller and Urey experiment.)


C. Fill in the blanks:

(a) Coacervates

(b) Reducing

(c) Alanine and glycine


B. Multiple Choice Questions:

A1. (b) Miller and Urey

A2. (a) Coacervates

A3. (c) Oxygen

A4. (b) Oparin and Haldane

A5. (c) Carbon dioxide


B. True and False Statements:

1. False (DNA is genetic material in the most of the organisms.

2. True

3. False ( Complex organic compounds were formed from simple organic

compounds under reducing conditions in Miller and Urey experiment.)


C. Fill in the blanks:

(a) Coacervates

(b) Reducing

(c) Alanine and glycine



Q1. What were sources of energy for chemical reactions involved in formation of complex organic compounds?

Q2. What did Oparin and Haldane propose?


Q1. Explain Miller and Urey experiment with the help of diagram?





Students, in previous topic of this chapter, you have learnt about origin of

life and formation of first living cell on this earth. With the passage of time,

number of new species of plants and animals were formed and evolved.


In our today’s topic we will discuss various morphological and anatomical evidences which proved the presence of more common characteristics and the closeness of the species. Also, the more closely related species are supposed to have had a common ancestor in the more recent past.


(ii) Thorn of Bougainvillea and tendril of Cucurbita both are modification of axillary bud.


(iii) Vertebrate hearts and brains:


(iv) Mouth parts of insects in each of these insects mouth parts comprise labrum, mandible maxilla etc.


(v) Potato and Ginger- both are modified shoots.


(v) Radish and Carrot- both are modified roots.


viii) Molecular homology- Homology found at molecular level. For example the plasma proteins found in the blood of man and apes are similar.


DIVERGENT EVOLUTION:When the same structures develop along different directions due to adaptations to different needs, this is called as I.Homology indicates common ancestry and based on divergent evolution.

 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.



(1) Drawin’s finches- During the journey of Galapagos Islands. Darwin observed an

amazing diversity of creatures of particular interest, small black birds later called

Darwin's Finches amazed him. Galapagos Island is situated near South America

which is a group of 22 smaller islands.

He realized that there were many varieties of finches at Galapagos 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.


(2) Australian Marsupials- A number of marsupials, each different from the other

evolved from an ancestral stock, but all within the Australian Island continent.


(3) Placental Mammals- A number of placental mammals have evolved from a common ancestral type in other parts of world also. Placental mammals in Australia also exhibit adaptive radiation.


ANALOGOUS ORGANS These organs perform the same function in but develop from different structures in different species, and this phenomenon is called as analogy.


Examples of analogous organs:


(i) Wings of bats, birds and insects- They are not anatomically similar structures

though they perform similar functions i.e. used for flying.


(ii) Flippers of Shark, Penguins and Dolphins


(iii) Sweet Potato (root modification)

and potato (stem modification)



When different structures evolve for the same function due to the similar habitat and

when more than one adaptive radiation appeared to have occurred in an isolated

geographical area (representing different habitats) this is called convergent

evolution.Analogy doesn't indicate common ancestry and it is based on convergent evolution where different group of organisms have similar adaptive features due to similar

habitat or towards the same function, hence analogous structures are a result of

convergent evolution.


VESTIGIAL ORGANS:These organs are non- functional and rudimentary in nature. However, they were very functional in the ancestors of the organism. This occurs due to the decreasing use of the organ which leads it to become small or non- functional in nature.Example of such a structure is the appendix and nictitating membrane in human




This can be called as the reverse of vestigial organs where a structure or organ which has become extinct in the species has appeared in the future generations. Example of such a trait is the appearance of a short tail in human babies.




(i) Multiple Choice Questions:


1. Which of the following sets do not have homologous organs:

a) Wings of mosquito and butterfly

b) Wings of butterfly and bat

c) Mouth parts of cockroach and butter fly

d) None of them


2. Wings of birds and wings of insects are example of:

a) Homologous structures and represent convergent evolution

b) Analogous organs and represent convergent evolution

c) Homologous structures and represent Divergent evolution

d) Analogous organs and represent divergent evolution


3. Homology is exhibited by:

a) Wings of butterfly, birds and bat

b) Paddle of whale, forearm of horse and forelimbs of man

c) Tail of monkey and bird

d) Sting of scorpion and honey bee


4. Flippers of penguin and Dolphin are examples of:

a) Convergent Evolution

b) Industrial Melanism

c) Natural Selection

d) Adaptive Radiation


5. is a vestigial organ:

a) Intestinal villi

b) Papillae

c) Vermiform appendix

d) None of the above


(ii) True/ False:

1. Organs which have common origin embryonic development but perform same or different functions are Analogous organs.


2. Vertebrate hearts is an example of Homologous organ.


3. When the same structures develop along different directions due to adaptations

to different needs, this is called as Adaptive radiation.


(iii) Fill ups:

1. Organs which have different origin but on perform similar functions are called as.


2. Small black birds in Galapagos Island during Darwin journey are known as



A) Multiple Choice Questions:


1. (0) wings of butterfly and bat are Analogous organs


2. (0) Analogous organs and represent convergent evolution as both have similar function but different structure.


3. (b) Paddle of whale, forearm of horse and forelimbs of man have similar structure but exhibit different functions.


4. (a) Flippers of penguin and Dolphin are examples of convergent evolution as their structures have evolve to perform same function.


5. (c ) Vestigial Organs are are non- functional and rudimentary in nature, e.g.

Vermiform appendix.


B) True/ False:

1. False Organs which have common origin embryonic development but perform

same or different functions are Homologous organs.

2. True

3. False When the same structures develop along different directions due to

adaptations to different needs, this is called as divergent evolution.


C) Fill Ups:

(1) Analogous organs

(2) Darwin finches



1. Define Homology and Analogy.

2. Explain Adaptive Radiation with example.

3. What do you mean by Convergent Evolution?



1. Describe Homologous and Analogous Organs with examples. How do they help in providing evidences for Evolution?








Evolution is unfolding of nature that brings about an orderly change from one form to another resulting in descendants becoming different from ancestors.There are many Evidences in support of evolution. In our previous topic, we have learnt about Morphological and Anatomical evidences.

Here we will discuss Embryological and Paleontological evidences.



Embryology provides a number of evidence related to embryonic stages of organisms which are called Embryological evidences. These are based on comparative developmental studies of embryos of various animals.

This theory was explained through following steps-


1. Similar early development: Development in sexually reproducing organisms begins from a single diploid cell stage, i.e. a fertilized egg or zygote. Zygote undergoes cleavage, blastulation and gastrulation. At the end of gastrulation, three germ layers are formed which give rise to various organs and organ systems.


2. Similar vertebrate embryos: Comparing the

embryos of vertebrates shows that all have gill slits except in fishes. This supports the idea that all the vertebrates share

common ancestors.


3. Temporary embryonic structures: There were

certain structures which were present’ in the

organisms at the early stages. There was evolution which leads to change in certain features. There are still certain structures which are observed in the early embryonic stage such as notochord is the rod-

like structure which is present in the larvae of certain vertebrates.There are gill clefts present in the embryonic structures in vertebrates.These structures provide evidence for evolution.


4. Haeckel's Biogenetic Law:Haeckel found similarities between embryonic development of an individual and evolution of the race. He formulated biogenetic law which is also popularly called Ontogeny recapitulates Phylogeny.Ontogeny is about growth and phylogeny is about evolutionary history.


5. Development of organs- The developmental pattern of organ development also leads to evolutionary links.



Study of paleontology shows that a number of organisms existed on earth for some time and then disappeared. They include the mighty dinosaurs, the toothed birds like Archaeopteryx, pteridosperms, giant horsetails, tree-like lycopods, great mammals, ancestors of man, trilobites, etc. Extinction occurred due to

(i) Competition from more advanced descendants.

(ii) Changes in environment.

(iii) Natural calamity.

(iv) Genetic degeneration.



The evidences of evolution based on the information collected from fossils are called Paleontological evidences.Fossils are preserved remains, impression or traces of any once living thing.Sometimes petrification occurs when the organic matter is completely

replaced by minerals and the fossil is turned to stone. It is evident that fossils hide many stories of evolution.Paleontological evidences are discussed through Connecting Links andMissing links.


CONNECTING LINKS:Connecting links are the organisms which have characteristics of two

different groups.


1. Duck billed platypus is a connecting link between mammals and reptiles. It has

mammary glands to feed and has hair on body and single aortic arch like mammals but lays

eggs with yolk and shell and similar pectoral girdle to reptiles.


2. Lung fish resembles the fish in having paired fins, gills and scales on its body, but it respires through lungs like  amphibians. Thus, lung fish acts as a connecting link between fish and



MISSING LINKS:These are those extinct organisms which had the characters of two different groups of animals and confirm the path of evolution as lie in-between these



Archaeopteryx:- It is a missing link between reptiles and birds. It was about the size of a crow and had both reptilian and avian characters.


Reptilian characters:-

(a)Presence of similar teeth in jaws.

(b) Each finger ending into a claw.

(c) A long tail with free caudal vertebrae.

(d) Presence of keelless sternum.

(e) Non-pneumatic bones.


Avian a characters:-

(a) Presence of feathers on the body.

(b) Rounded cranium with intimate fusion of bones.

(c) Forelimbs modified into wings and have only three fingers.

(d) Presence of 4-toes in each foot and adapted for perching as in the birds.

(e) Presence of furcula or wish-bone.

(f) Jaws modified into beak.


These characters show that the birds have evolved from the reptilian ancestors.




(a) Multiple choice questions:


(1) Name a fossil bird which looks like a bird but has many other features found in reptiles?

(a) Dodo

(b) Archaeopteryx

(c) Flamingos

(d) Mouse Bird.


(2) Aves have evolved from:

(a) Amphibians

(b) Arthropods

(c) Mammals

(d) Reptiles


(3) Haeckel’s law of evolution is related to-

(a) Embryonic evidences

(b) Paleontological evidences

(c) Morphological evidences

(d) Cytological evidences


(4) Connecting links support-

(a) Embryonic evidences

(b) Paleontological evidences

(c) Morphological evidences

(d) Cytological evidences


(5) Duck billed Platypus is a connecting link between -

(a) Non-living and living

(b) Algae and Fungi

(c) Reptiles and Mammals

(d) Pisces and Amphibians


(b) True /false:

(1) Embryology provides many evidences in support of evolution.

(2) Evolution is a gradual process.

(3) Archaeopteryx is living bird.


(b) Fill ups:

(1) Duck billed platypus is a connecting link between reptiles and

2) Fossils are remains, traces or impressions of once..........



1. Multiple Choice Questions:


1 (b) Archaeopteryx

2.(d) Reptiles

3 (a) Embryological evidences

4.(b) Paleontological evidences

5 (c) Reptiles and mammals


2. True/ False:

(1) True

(2) True

(3) False Archaeopteryx is a fossil organism which is a missing link between reptiles and birds.


3. Fill ups:

(1) Mammals

(2) Living



(1) Define Biogenetic Law and give evidence in support of it.

(2) Write about avian and reptilian characters of Archaeopteryx.

(3) Differentiate between connecting links and missing links.



(1) How do embryological and paleontological evidences support Evolution?





Students, as you have learnt from previous topics that there are many Evidences in support of evolution. We have learnt about Morphological,Anatomical, Embryological and Paleontological evidences. Here we will

discuss about Bio geographical, i! [NS and Cytological evidences of evolution.


Biogeography is the pattern of distribution of animals and plants in different parts of

the earth. It shows the evolutionary interrelationship between living organisms.

Biogeographical evidences of evolution on the basis of geographical distribution of

species were documented by Charles Darwin, an English naturalist.On the basis of distribution of plants and animals on the earth, A.R, Wallace (1876 A.D.), an English naturalist, divided the earth into six biogeographical realms:Palearctic, Oriental, Ethiopian, Australian, Nearctic and Neotropical. These realms are separated from one another by major barriers like sea, deserts, maintaining e.g.Oriental biographic realm, which includes India also, is isolated from palearctic realm by Himalayan mountains and from Australian and Ethiopian realms by seas.It is believed that around the Carboniferous period of Paleozoic era (about 375 million years ago), there was a single land mass called Pangea land mass. Later

on, due to various geological changes, especially movements of crustal plates

below the surface of the earth (called tectonic movements), this huge land mass

was broken into smaller land masses which drifted away from one another. These

land masses became different continents and got separated from one another by

the barriers, especially sea, which now prevented the free movements of living

organisms. As these land masses had different environmental conditions, the

plants and animals evolved differenily.


1. Darwin’s Finches:Charles Darwin found that the Galapagos Islands have many endemic

species of plants and animals. He noticed that on these islands, insect-eating

Warbles and Woodpeckers were absent but reported various types of finches (a group of small sized and black colored passerine birds of Geospizae family). Darwin found that the finches (about 20 varieties), found on different islands of Galapagos with varied environmental conditions, differ from one

another mainly in SIZE and BILL (BEAK) SHAPE due to different feeding habits but were closely related to one another. These birds are now called Darwin's finches.Dr. David lack proposed that these birds have

evolved from a common ancestral seed-eating

ground finches and living in a_ particular

geographical area of South American mainland.

But later these finches radiated to different

geographical areas and adapted differently in their feeding habits so developing different type of beaks e.g. woodpecker like, insectivorous feeding,vegetarian, cactus-feeding, warbler finch, etc.Such an evolutionary process, in a given

geographical area starting from a common

point and giving rise to new species adapted to new habitats and ways of life, is called Adaptive Radiation.


2. Discontinuous distribution:When descendants of a common ancestor inhabit different geographical areas and differ from each other, it is called discontinuous distribution, the Alligators are found only in south-eastern United States and

eastern China and are different from each other. It was suggested that during

early Cenozoic era, North America and East Asia were in continuity by a land bridge in the Bering Strait region and there was free movement of alligators and other organisms. So Alligators were distributed over the entire region. In late Cenozoic era, barriers were developed between these areas and

distribution of Alligators became discontinuous. As these areas had different

environmental conditions, the Alligators of two areas developed different mutations (variations) so they became slightly different but are related species of the same genus. It is supported by the occurrence of Magnolias,Tulips and Sassafras plants in the eastern U.S.A and China only.


3. Restricted distribution:When some unique organisms are confined in some parts of the world, due to their habitat isolation, it is called restricted distribution e.g. Egg-laying mammals (Prototherians e.g. Duck billed platypus and spiny ant-eater) and

marsupials (Metatherian e.g. Kangaroos) are restricted in Australian only but

this continent has only few placental mammals.The evidences based on similar biochemical reactions are called biochemical

evidences e.g. similarities in DNA, proteins, genes, etc.


1. Enzymes:Similar enzymes of different animals are similar in their chemical nature and mode of action e.g.Enzyme Substrate End product/s Amylase — Starch Maltose

Trypsin Proteins Proteoses/ peptones

(From protozoans to man, so called ancient enzyme).


2. Hormones Similar hormones of different vertebrates are similar in their chemical nature,target organ and mode of action e.g.

Hormone Source Function Insulin Pancreas (B-cells) Glycogenesis Insulin of different vertebrates is similar, so the deficiency of insulin in man can be compensated by giving insulin derived from the pancreas of other

animals. Similarly, thyroxine hormone of human thyroid gland can induce metamorphosis in tadpole larva of frog.


3. Cytochrome ‘C’:This is an electron-carrier protein found in ETC of mitochondria of all living organisms. Its amino acid sequence was determined by R.E. Dickerson 0972 in different organisms.


3. Blood and Lymph:The components of blood and lymph, and their functions are similar in different vertebrates.


4. Blood proteins: (Haematin crystals) Precipitation test confirm not only

similarly but also degree of evolutionary and serological relationship between the vertebrates.


5. Blood Groups: Four blood groups A, B, AB and O are found in Apes but not in Monkeys. These studies showed that man is more closely related to apes than to monkeys though all the three have a common ancestry.


6. Limulus is closer to Arachnids than to Crustaceans.


7. Hemichordates are closely related to Echinoderms.


8. Excretion: Physiology of excretion also confirms evolution e.g.

(a)The adult frog is ureotelic in excretion while its tadpole larva shows ammonotellic like fishes.

(b)The youngone of a bird is first ammoniotelic, then ureotelic and finally



9. ATP is universal energy molecule.

SIGNIFICANCE These similarities between living organisms at the molecular level is called molecular homology.These similarities confirm the relationship of all organisms ad show their descendance from a common stock.

ee:Taxonomic characters are the taxonomic attributes that can be used to provide the

evidence from which relationships (the phylogeny) between taxa are inferred”.


We study taxonomic evidences in relation to:

1. Morphology (deals with the external characters)

2. Anatomy (The study of the structure of organism and their parts)

3. Palynology (The study of plant pollen, spores)

4. Embryology (The study of embryo)

5. Cytology (The study of structure and function of cells)

6. Phytochemistry (The study of phytochemicals, which are chemicals

derived from plants)

7. Ultra-Structure (The architecture of cells and biomaterials that is visible at

higher magnification)

8. Genome Analysis and Nucleic Acid hybridization (Identification,measurement, arrangement of genomic features).



All the living organisms are similar in being:

{1. Cellular in nature and are formed of one (protozoans) or more cells (metazoans).


2. Presence of similar organelles having similar ultrastructure and functions.


3. In all, the cells are formed of similar material called protoplasm having similar

physical, chemical and biological properties.


4. Basic metabolic cellular functions are performed in a similar way.These support that all the organisms are interrelated and have common ancestry.



(a) Multiple choice questions:


1. Darwin in his ‘Natural Selection’ theory did not believe in any role of which of the following in organic evolution?

a) Survival of the Fittest

b) Struggle for existence

c) Discontinuous variations

d) Parasites and Predators as natural



2. Egg laying mammals and marsupials are restricted to :

a) Australia

b) Asia

c) South America

d) Antartica

 3. The conceptual evolution was given by:

a) Darwin

b) Aristole

c) Lamarck

d) Empedocles


4. Darwin Finches are related to which of the following evidences?

a) Fossils

b) Embryological

c) Anatomical

d) Biogeographical


5. Four blood groups A, B, AB and O are found in:

a) Man

b) Apes

c) Monkey

d) Both (a) and (b)


(b) True /false:

(i) | Archaeopteryx is a connecting link between reptiles and birds.

(ii) A.R. Wallace, divided the earth into six biogeographical realms.

(iii) | Evolution is a discontinuous process.


(c) Fill in the blanks:

(i) Darwin finches are examples of evolution.

(ii) is universal energy molecule.




(a) Multiple Choice Questions:

1. c) Discontinuous variations According to this theory, organic evolution is a

continuous process

2. a) Australia

3. a) Darwin

4. d) Biogeographical

5. d) Both (a) and (b)


(b) True /false:

(i) False Archaeopteryx is a Missing link between reptiles and birds.

(ii) True

(iii) False Evolution is a continuous process


(c) Fill in the blanks:

(i) Divergent

(ii) ATP


1. What are Tectonic Movements?

2. Write six Biogeographic Realms?

3. Define convergent evolution?

4. What is molecular Homology?


1. Write in detail about Darwin's finches.

2. Write about Biochemical Evidences in the process of evolution.





Students in this topic we will learn about the theory of organic evolution put

forward by French naturalist, Jean Baptiste de Lamarck(1744-1829A.D.)THEORIES OF EVOLUTION Buffon (1707-1788), Erasmus Darwin (1731-1802 A.D.) also proposed idea

of evolution through environmentally controlled forces. So main theories of

evolution are:

1. Lamarckism or Theory of Inheritance of Acquired characters.

2. Darwinism or Theory of Natural Selection.

3. Mutation Theory by Hugo de Vries


Lamarckism:Lamarckism is also known as Theory of inheritance of acquired characters

published in Philosphic Zoologique in 1809 A.D. by Lamarck .His theory is based on the inheritance of acquired characters which are defined as the changes developed in the body of organism from normal characters,in response to the changesin environment,or use and disuse of organs,in their own life time,to fulfil their new needs.


Postulates of Lamarckism:

1. New needs or Wants: a change in environmental factors leads to changes in habits or behaviour. This tendency leads to complexity of organs.


2. Use and disuse of organs: It greatly affect the form, structure and functioning of organs. Continuous and excessive use make organs more efficient while their disuse leads to degeneration and disappearance.


3. Inheritance of acquired characters: Acquired characters are inheritable and are transmitted to the offsprings.


Lamarck’s two factor theory involves-

a) A complexifying force that drives animal body plans towards higher levels.


b) An adaptive force that causes animals with a given body plan to adapt to circumstances (use and disuse of organs, inheritance of

acquired characters).


Lamarck explained that organisms have a tendency to become complex.


Evidences in favour of Lamarckism:

1. Phylogenetic studies of horse, an elephant and other animals show that all forms transformed from simple to complex one.


2. Giraffe developed long neck and fore limbs by their extra use from deer like ancestors.


3. Snakes developed from limbed ancestors( disuse and degeneration of organs.


4. Aquatic Birds develops webs and reduction in wings (use and disuse of organs)


5. Flightless Birds viz Kiwi, Ostrich lost their flying habits(continuous disuse

of wings)


6. Horse has developed from very short legged and more functional digits (4 functional fingers and 3 functional toes) Dawn Horse, change in habitat(from soft ground to dry ground) leads to modern day Horse.


Criticism of Lamarkism:Theory of continuity of germplasm by German Biologist August

Weismann in 1892 A.D. states that only germ cell changes are carried to next generations and not by somatic cells.


Weismaan worked on mice for 22 generations by docking tails,but none of mice born tailless.


Similarly piercing of nose and ear in Indian women for generations does not result in hole either in nose and ear in offspring.



1. Lamarckism was first comprehensive theory of Biological Evolution.

2. It stressed on adaptation to environment as a primary product of evolution.



Recent findings in Environmental role in evolution revived Lamarckism as

Neo-Lamarckism.The term was coined by Alphaeus S. Packard, French Giard, American Cope, T.H.Morgan, Spencer, Packard,Bonner, Tower, Naegali and Mc Dougal contributed Neo-Lamarckism.


Salient features of Neo-Lamarckism:

1. Germ cells may develop from somatic cells (a) Regeneration in


(b)Vegetative Propagation in Bryophyllum

(c) A part of zygote

(equipotential egg) of human can develop into complete foetus(Driesch).


2. Effect on germ cell through somatic cells pale variety of Moth ,when fed on Manganese coated food,a true variety of melanic moth is produced.


3. Effect of environment directly on germ cells when some young potato beetles reared in variable temperature ,marked changes in body coloration observed in next generation.

Conclusion:Lamarckism and Neo-Lamarckism explain us the role of environment in

evolution can't be kept aside.






(1) The theory of Lamarck was published in -

(a) Origin of Species

(b) Philosophie Zoologique

(c) Intracellulare Pangenesis

(d) None of these


(2) The key words of Lamarack’s theory is about —

(a) Germ plasm

(b) Natural Selection

(c) Use and disuse of organs

(d) big bang


(3) Lamarck stated that organisms have tendency to become-

(a) simple

(b) complex

(c) stable

(d) none of these


(4) Long neck of giraffe is an example of —

(a) acquired characters

(b) natural selection

(c) theory of germ plasm

(d) none of these


(5) Flightless birds like ostrich are example of-

(a) use of organs

(b) variations

(c) mutations

(d) disuse of organs



1. Snakes evolved from lizards.

2. Devries appreciated lamarck’s theory.

3. The theory of ‘Use and disuse of organs ‘was given by Darwin.



1. Lamarck’s theory was later on accepted as ..........

2. Development in genetics led to failure of............



1) (b) Philosophie Zoologique

2) (c) use and disuse of organs

3) (b) complex

4) (a) acquired characters

5) (d) disuse of organs



1. True

2. False De vries gave theory of Germplasm. This concept failed Lamarck’s theory.

3. False ‘Use and disuse of organs ‘ was given by Lamarck


(c) FILL Ups:

1. Neo Lamarckism

2. Lamarckism



3. What do you understand by acquired characters?

4. Write postulates of Lamarack’s theory.

5. Write about Neo Lamarackism.



1. Discuss the theory of evolution given by Lamarck with the help of suitable examples.





Charles Darwin (1809-1882 A.D.). The English naturalist was the most dominant figure among the biologist of the 19" century. He explored

Galapagos Island on H.M.S. Beagle (a ship in which Charles Darwin sailed around the world) and other islands nearby. He collected the observations on animal distribution and relationship between living and extinct animals. They found that existing living forms share similarities to varying degree not only among themselves but also with life forms that existed millions of years ago.

Darwin explained his theory of evolution in a book entitled on The origin of species by means of natural selection. It was published on 24" November 1859.


Charles Darwin is known as the father of evolution due to his contribution to

the establishment of the theory of evolution. His theory helped in removing all

the conventional old believes which said that the formation of various species was a supernatural phenomenon or act of the Almighty. Darwin's evolutionary theory of natural selection gave a more rational explanation of the formation of new species. As per natural selection, various species

originated from a single species as a result of adaptation to the changing environment.



Darwin explained his theory with following postulates:

1. Geometric increase

2. Limited food and space

3. Struggle for existence

4. Variations

5. Natural selection of survival of the fittest

6. Inheritance of useful variations

7. Speciation


1. Geometrical increase > According to Darwinism,the population tend to multiply geometrically and the reproductive power of living organisms are much than required to maintain their number.e.g. Paramecium divides three times by binary fission in 24 hours during favourable conditions.A female rabbit gives birth to six young ones in one

litter and produces four litters in a year. Six- month-old rabbit is capable of reproduction. If all the rabbits

survived and multiplied at this rate, their number would be very large after some time.

Thus some organisms (living beings) produce more offspring and others produce

fewer offspring. This is called differential reproduction.


2. Limited food and space > Darwinism states that though population tends to increases only arithmetically, food , space and other resources remain limited.They are not liable to increase.


3. Struggle for existence > The struggle for existence can be of three types.


(a) Intraspecific > It is the struggle

between the individuals of the same

species because their requirements

like food, shelter, breeding places, etc.

are similar.e.g. Many human wars are the examples of intraspecific struggle.

Two dogs struggling for a piece of meat.


(b) Interspecific > It is the struggle

between the members of different

species. This struggle is normally for

food and shelter.e.g, A fox hunts out a rabbit, while the fox is preyed upon by a tiger.


(c) Environmental or Extra specific > It

is the struggle between living organisms and adverse environmental factors like heat, cold, drought, flood,earthquake etc. Thus, climate and other natural factors also help in restricting the number of individuals of

particular species.


4. Variations > Variation is the law of nature. According to this law, no two individuals except identical twins are

identical. Due to the variations

some individuals would be better adjusted towards the surroundings than the others.

According to Darwin, the variations are gradual (continuous) and those which

are helpful in the adaptations of an organism towards its surroundings would be passed

on to the next generation,while the others disappear. <=


5. Natural selection or survival of the fittest > Nature selects only those

individuals out of the population which are with useful continuous variations.



6. Inheritance of useful variations >

Darwin believed that the selected individuals

pass their useful continuous variation to their offsprings who are born fit to the changed environment.


7. Speciation > According to Darwinism,

useful variations appear in every generation

and are inherited from one generation to

another. After some generations these

continuous and gradual variations in the

possessor would be so distinct that they form

a new species.


CRITICISM OF THE NATURAL SELECTION THEORY/DARWINISM Darwin was unable to explain the basis of variation and the mode of transmission of the variants to the next generation. He failed to explain following concepts:


1. The inheritance of small variations in those organs which can be useof only when fully formed. Example, wings of a bird.


2. Inheritance of vestigial organs.


3. Inheritance of over specialised orange. Example, antlers in deer and tusks in elephants.


4. Presence of neuter flowers and sterility of hybrids.


5. Did not differentiate between somatic and germinal variations.


6. He did not explain the cause of the variations and the mode of transmissions of was also refuted by Mendel’s laws of inheritance.








(a) Multiple choice questions:


1. Darwin in his natural selection theory did not believe in any role of which of the following in organic evolution

(a) Survival of the fittest

(b) Struggle of existence

(c) Discontinuous variations

(d) Parasites and predators as natural enemies


2. Natural selection really means

(a) Struggle for existence

(b) Differential reproduction

(c) Survival of the fittest

(d) Elimination of the unfit


3. The corner stone of Darwin’s theory is

(a) Inheritance of acquired character

(b) Higher productivity

(c) Natural selection

(d) None of these


4. The concept of evolution was given by

(a) Darwin

(b) Aristotle

(c) Lamarck

(d) Empedocies


5. Darwin’s finches are related to which of the following evidences:

(a) Fossils

(b) Embryological

(c) Anatomical

(d) Bio- geographical


(b) Fill Ups:

1. The most accepted theory of origin of life was proposed by and .

2. Darwin's finches are examples of selection.


(c) True/False:

1. The book “Origin of life” was written by Oparin and Haldane.

2. Darwin supported struggle of only those organisms which for existence.

3. Natural selection of Neo-Darwinism operates through differential




1. (c) Discontinuous Variations

2. (c) Survival of the Fittest

3. (a) Inheritance of the acquired characters

4. (a) Darwin

5. (d) Biogeographical evidences



1. A.| Oparin and |.B.S Haldan

2. Natural



1. False; the book “Origin of life” was written by Darwin.

2. True

3. True



1. Explain briefly the struggle for existence in Darwinism.

2. Define Speciation.



1. Explain Darwin theory of natural  selection.





Hugo de Vries in his book Die Mutation Theory (1901) proposed the mutation theory in order to explain the mechanism of evolution.

This theory was based on his observations on Evening Primrose, Oenothera lamarckiana. He studied this plant in wild (natural) forms for many years continuously and observed certain spontaneous changes in some of these wild plants. These plants differed considerably in stem height, flower colour and leaves shapes. He observed that these changes were heritable and ultimately led to

several new varieties.He succeeded in cultivating all these new varieties and named them as mutant varieties.


In fact, he selected for his breeding experiments two mutant varieties—Oenothera

laevifolia, characterized by smooth leaves and O. brevistylis characterized by short

styles. And he observed that these features were breeding true and so he regarded these mutant strains as the distinct species.


MUTATION THEORY:On the basis of above observations, Hugo de Vries (1901) put forward a theory of evolution, called mutation theory. The theory states that evolution is a jerky process where new varieties and species are formed by mutations (sports or

 discontinuous variations) that function as raw material of evolution.

The salient features of mutation theory are:


1. Mutations, sports or discontinuous variations are the raw material of evolution.


2. Mutations appear all of a sudden. They become operational immediately.


3. Unlike Darwin's continuous variations or fluctuations, mutations do not revolve

around the mean or normal character of the species.


4. The same type of mutations can appear in a number of individuals of a species.


5. All mutations are inheritable.


6. Mutations appear in all conceivable directions.


7. Useful mutations are selected by nature. Lethal mutations are eliminated.

However, useless and less harmful ones can persist in the progeny.


8. Accumulation of variations produces new species. Sometimes a new species is

produced from a single mutation.


9. Evolution is a jerky and discontinuous process.



1. The mutation theory describes the importance of mutation in selective value of



2. It explains the occurrence of evolutionary changes within short period in contrast

to natural selection which describes slow and continuous variations.


3. Mutation theory explains the absence of connecting links as no criteria against

evolution but its possibility exist.


4. Occurrence of mitosis in all possible directions removes the possibility of

species disappearance by crossing.


5. Induced mutations have given rise to new useful varieties.



1. It could not explain the existence of discontinuity in distribution among



2. Many mutations, described by de Vries in O. lamarckiana, are known to be due

to certain numerical and structural changes in the chromosomes. For instance,“gigas” mutant of O. lamarckiana was later found to be due to polyploidy.


3. Mutation theory alone could not explain evolution. It, however, provided raw

material for other forces to act upon it and bring about evolutionary changes.


4. Mutation theory cannot satisfactorily explain the development of mimicry, mutual

dependence of flowers and pollinating insects.




A) Multiple Choice Questions


1. Sudden heritable changes are called


(b) Variations

(c) Recombination

(d) Evolution


2. According to De Vries theory, evolution is

(a) jerky

(b) discontinuous

(c) continuous and smooth

(d) both a and b


3. Mutation may be described as

(a) Continuous genetic variation

(b) Phenotypic change

(c) Discontinuous genetic variation

(d) change due to hybridisation



4. Mutation theory was proposed by


(b) Lamarck

(c) De Vries

(d) Mendel


5. Theory of mutation by de Vries considers that

(a)Only small mutation take part in developing variations

(b) Only large

mutation take part in developing variation (c) Both small and large mutations

cause variations

(d) None of the above


B) True/ False:

1. Abrupt hereditary changes are called mutations.

2. Mutations appear in all conceivable directions.

3. All mutations are not inheritable.


c) Fill ups:

1. Mutation theory was based on his observations on plant.

2. Induced mutations have given rise to new varieties.



A) Multiple Choice Questions:


1. (a) Mutations- Mutations are sudden heritable changes.


2. (c) Both a & b- Evolution is a jerky and discontinuous process according to De Vries,.


3. (c) Discontinuous genetic variation- Mutation may be described as discontinuous genetic variation.


4. (c) De Vries- Mutation theory was proposed by De Vries.


5. c) Both small and large mutations cause variations- Theory of mutation by de Vries considers that both small and large mutations

cause variations.


B) True/ False:

1. True- Sudden, jerky, heritable changes are called Mutations.

2. True- Mutations appear in all conceivable directions.

3. False- All mutations are inheritable.


c) Fill Ups:

1. Mutation theory was based on his observations on Oenothera lamarckiana plant.

2. Induced mutations have given rise to new useful varieties.


1. Enlist a few advantages of Mutation Theory.

2. Write note on De Vries observations on Evening Primrose.

3. What are the objections to Mutation Theory?





Students, after keenly observing it came in light that neither Darwin theory nor

Lamarck theory explain process of Evolution completely. Then Huxley proposed a theory of Evolution called Modern theory or synthetic theory of evolution.He considered ‘Population’ as a unit of Evolution.The modern synthetic theory of evolution describes the evolution in terms of

genetic variations in a population that leads to the formation of a new species.It explains the contribution of factors such as genetic variations, reproductive and geographical isolation, and natural selection.


GENETIC VARIABILITY:Variation is a key to evolution and different kind of variations occur in nature due to Mutations, recombination of genes and Hybridization



Mutations occur on both Chromosomal and Gene levels. Studies showed that the unit of heredity and mutations are genes and these are located in linear manner on chromosomes. Change in genetic material changes phenotype

(morphology) of and individual.



Various sources of genetic variability are:-

1. Mutations:- These are sudden and inheritable changes in genetic material. These are of three types on the basis of nature of genetic material involved.


(a) Chromosomal aberrations: - These are morphological changes in chromosomes without changing their number means addition or loss of some genetic material of a chromosome. These can be :


7 Deletion: Itis the loss of a chromosome segment.


Duplication: It is duplication of a segment of chromosome.


Translocation: It is exchange of chromosome segments between non homologous chromosomes.


Inversion: Here, chromosomal segments get inverted and it is further of

two types-

(i) Paracentric: Inversion does not involve centromere.


(ii) Pericentric: Inversion involves centromere.


Isochromosome: Replacement of lost Chromatid with identical copy of homologous chromatid.


Ring Chromosome: A ring chromosome is formed when two breaks occur in a chromosome, giving rise to two sticky ends that reunite to form a ring.


(b) Numerical chromosomal mutations: - It include change in number of chromosomes. These can be:


Euploidy (gain or loss of number of genomes or set of chromosomes)


Aneuploidy (gain or loss of one or two chromosomes)


(c)Gene mutations: -These are invisible changes in chemical nature of a

gene and are of three types:


Deletion-Loss of one or more nucleotide pair


Addition-Gain of one or more nucleotide pair


Substitution-Replacement of one or more nucleotide pair with another base pair


2. Recombination of genes:- During prophase-1 of crossing over thousands of new combination of genes occur and these form different phenotypes.


3. Hybridization:- It involves interbreeding of two genetically different individuals to produce hybrids


4. Mutagens:- These can be physical i.e. radiations,temperature or chemical nitrous acid,colchicine,nitrogen mustard etc.


5. Genetic drift:-Extreme reduction in population due to epidemic or migration may cause loss of some genes of original characteristics of a species which lead to speciation after many generations. This is also called Sewell Wright Effect.



It differs from Darwinism that it does not operate through ‘Survival of fittest’

rather operate through comparative reproductive SUCCESS.

Those members, which are best adapted to the environment, produce at a

higher rate and produce more offsprings than those which are less adapted. So

after a number of generations better and different quality of gene pool exists:

which leads to speciation.



Some natural calamities such as flood, fire etc. can lead to isolation of a group of

population which reduces chance of interbreeding between related (isolated)

group of individuals. These isolated gene pools grow generation after generation

and may lead to different phenotypes, hence speciation.Reproductive isolation is the prevention of interbreeding between the

populations of two different species. It maintains the character of a species but

can lead to the origin of a new species. This can be achieved by-


1. Geographical isolation — It refers to the separation of groups of related organisms by physical barriers, such as sea, mountain, desert, river, etc.


2. Temporal Isolation — It is the failure of two species to interbreed because

they breed at different times of the year.


3. Behavioural Isolation — It prevents interbreeding of two groups due to

differences in courtship and mating behaviour.


4. Mechanical Isolation — It is the difference in size or structure of genitalia

between species that makes interbreeding difficult or impossible.


CONCLUSION:EVOLUTION is the change in the characteristics of a species over several 

generations and relies on the process of natural selection.


The theory of evolution is based on the idea that all species are related and gradually change over time.


Evolution relies on there being genetic variationin a population which affects the physical characteristics (phenotype) of an



Some of these characteristics may give the individual an advantage over other individuals which they can then pass on to their offspring.






1) Who gave synthetic theory of evolution?

(a) Hugo de vries

(b) Huxley

(c) Lamarck

(d) A R Wallace


2) What is the unit of evolution according to the Modern theory of evolution ?

(a) Individual

(b) Chromosome

(c) Population

(d) Gene


3) Spread of genes from one breeding population to another by migration,

which may result in change in gene frequency is called:

(a) Genetic drift

(b) Gene frequency

(c) Gene flow

(d) none of these



4) A sudden change occurred in chromosome is called:

(a) Mutation

(b) variation

(c) evolution

(d) none of these


5) Which one of following is not a mutagen?

(a) Radiations

(b) Colchicine

(c) Nitrous acid

(d) HCl



1) Species formation is the final result of evolution

2) Trisomy is an example of Numerical Chromosomal Mutation.

3) Evolution is a continuous process.



1) Elimination of some genes of original characteristics of species occur

due to extreme reduction in a population is called....................effect.

2) Instant speciation occurs by ..................



(1) (6) Julian Huxley coined this term in his 1942 book,Evolution: The Modern Synthesis.


(2) (c) The Modern Synthetic theory of Evolution explains the evolution of life in

terms of genetic changes occurring in the populations that leads to the formation

of new species


(3) (c) Gene flow can take place between two populations of the same species through migration, and is mediated by reproduction and vertical gene transfer from parent to offspring.


(4) (a) Mutation

(5) (d) Mutagens are chemical compounds or forms of radiation (such as ultraviolet (UV) light or X-rays) that cause irreversible and heritable changes (mutations) in the cellular genetic material, deoxyribonucleic acid (DNA).



(1) True

(2) True

(3) True



(1) Sewell wright

(2) Hybridization





1) What is concept of natural selection according to modern theory of evolution?

2) What do you mean by gene flow?

3) What do you mean by Reproductive Isolation?



1) Describe Modern theory of organic evolution?





Reproductive isolation: The prevention of mating between two natural populations of the SAME or DIFFERENT species due to presence of barriers to interbreed is called reproductive isolation.Hardy-Weinberg principle or Hardy-Weinberg equilibrium model:

It is the fundamental law which provides the basis for studying Mendelian populations developed by GH Hardy and G Weinberg in 1908.

It states that Allele and genotype frequencies in a population will remain

constant from generation to generation in the absence of other evolutions influences like genetic drifts, natural selection, selective mating and mutation,etc.


REPRODUCTIVE ISOLATION:The various preventions to interbreeding have been called ISOLATING MECHANISMS by, Dobjhanky.


Operation of Reproductive isolating mechanisms is important for the formation of

new species and to maintain the distinct identity of different species.


The barriers for isolation can be PHYSICAL or BIOTIC, PRE-MATING or POST-MATING.


PHYSICAL barriers are of three types:

1. Geographical

2. Spatial

3. Ecological


BIOTIC barriers are:Temporal (Seasonal), Ethological (Behavioural), Mechanical (Difference in position,size of genet ilia), Physiological (Absence of specific pheromones) and Genetic

(post mating).


HARDY-WEINBERG PRINCIPLE:Different ways to form genotypes for next generation can be shown in Punnette Square, where proportions of each genotype are equal to the product of rows and columns, Allele frequencies from the current generations.

Sum of genotype frequencies, (p + q) = p- + q- + 2pq

Hardy-Weinberg equation used to determine genotype frequencies;

Where,p? — represents the frequency of dominant homozygous genotype (AA)

q?— represents the frequency of recessive homozygous genotype (aa)

 pq —represents the frequency of heterozygous genotype (Aa)

The major factors affecting the Hardy - Weinberg's equilibrium:


1. EEE |n small population frequencies of particular allele may change drastically by chance alone, such change in allele frequency occurs randomly as if the frequencies were drifting is known as Genetic drift.

Genetic drift occurs by 2 factors:


1)Founder effect — Formation of different genotypes in new settlement is called

founder effect. When a small group of persons called founders leave their place

of origin and find new settlements, the population in the new settlement may

have genotype frequency from that of parent population.


2) Bottleneck effect — Due to natural disaster like earthquakes major

population declines. A few surviving individuals may constitute a random genetic

sample of original population. The resultant alterations and loss of genetic variability

has been termed Bottleneck effect.

ee — Movement of individual from one place to another is called Migration which is powerful agent of change because of members of two

different populations may exchange genetic material. The new-comer individual has

unique combination and is well adapted, it alters the genetic composition of receiving

population. This is the gene flow from one _ population to another.

GN — It is a sudden and heritable change in an individual which is due to

change in base sequence of nucleic acid in genome of the individual which causes

large variation and new species formation.

EE Environmental conditions determine that which individual in population produces the maximum number of offsprings. Organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success which causes evolution and disturbs the equilibrium.


Let us know what we have learnt!


MCQ's :

1. Which of the following options would not disrupt Hardy-Weinberg equilibrium in a population?

(a) Random mating

(b) Genetic drift

(c) Natural selection

(d) Mutation


2. Which term describes the theory that alleles or proportions of genotype ina population will remain constant or stable as long as individuals in population randomly mate with each other?

(a) Genetic drift

(b) Evolution

(c) Genome

(d) Hardy-Weinberg equilibrium


3. In Hardy-Weinberg equilibrium equation q? is the frequency of what?

(a) Recessive homozygous allele

(b) Dominant homozygous allele

(c) Heterozygous allele


4. Which of the following would cause deviation from the Hardy-Weinberg equilibrium?

(a) Small population

(b) Random mating

(c) Lack of selection pressure

(d) No mutation


5. Which of the following formulae predicts the genotype frequency of the next generation?


(b) e = mc?

(c) x? = sum [(0-c)*/*]

(d) p? + 2pq +q? = 1


True/ False:

(a) Random meeting affects the Hardy Weinberg equilibrium

(b) A large population favour the Hardy Weinberg equilibrium model.


Fill in the blanks:

(a) Founder effect is the main factor to cause

(b) A sudden and suitable change in an Organism is called

(c) Complete Hardy-Weinberg equilibrium equation p?+q?+_ = 1


MCQ's -

1. (a) Random mating

2. (d) Hardy-Weinberg equilibrium

3. (a) Recessive Homozygous allele

4. (d) Lack of selection pressure

5. (d) p? + 2pq + q?= 1



(a) False ( Mating by chance not by individual interest )

(b) True


Fill in the blanks:

(a) Genetic Drift

(b) Mutation

(c) 2pq



1. What do you mean by reproductive isolation?

2. What is genetic drift?

3. What do you understand from gene flow?

4. Which fundamental law provides basis for studying the Mendelian population?




1. Explain factors which affect the Hardy Weinberg equilibrium principle




Students, in previous topics, you have learnt that the theory of evolution is one of

the great intellectual revolutions of human history, drastically changing our

perception of the world and of our place in it. Sir,;Charles Darwin put forth a

coherent theory of evolution and amassed a great body of evidence in support of

this theory.In today’s topic we will discuss Darwin's discovery of natural selection, Artificial selection and the concept of Speciation.



Natural Selection is a process of adaptation by an organism to the changing environment by bringing selective changes to its genotype or genetic composition.It is one of the four primary mechanisms of evolution along with mutation, genetic drift and migration.


Charles Darwin Popularized the concept of natural selection during his studies on



In 1831, Darwin got an opportunity to travel on [EEN (A ship in which Charles Darwin sailed around the world) for a voyage of world exploration that lasted for 5 years (1831-1836). During that period Darwin

explored the fauna and flora of a numbers of continents and Islands. Later beagle was sailed to the GALAPAGOS ISLANDS.


Darwin noticed finches of Galapagos Islands. These birds were called


Finches found on different Islands of Galapagos have different types of EEE

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. 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 J



According to Darwin, natural selection is not an intentional process and is brought about by changes in environment. It is a fundamental process of evolution in which any characteristics of an Individual that allows it to survive and reproduce with the changing environment condition will be selected by

nature and will gradually appear in all the species.


Population of all organism have variations in characteristics which help them to adapt better to environment. Some of these characteristics enable individual to survive better in natural condition and reproduce. This is called SURVIVAL OF THE FITTEST. The organisms which adapt well in the

environment are selected by nature and thus survive more in nature. This is called NATURAL SELECTION.




1. Industrial melanism: In England it was observed that Biston betulana (peppered moth) existed in two strains (forms). Light coloured (white) and malanic (black) In the past, bark of tree 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. Thus Industrial melanism supports evolution.


2. Antibiotic Resistance: We use antibiotics or drugs to kill disease causing Bacteria. When a bacterial population encounters a particular antibiotic sensitive to it die. But some bacteria having mutations become resistant to 

the antibiotic. Such resistant bacteria survive and multiply quickly as the

competing bacteria have died. Soon the resistance providing genes become wide spread and entire bacterial population becomes resistant.


3. Resistance of Insect to Pesticides:

Within few years of introduction of DDT,new DDT resistant mosquitoes appeared

in the population. These Mutant strains soon become well established in

population and to the great extent replaced the original DDT sensitive


Human has created many varieties of plants and many breeds of animals for

his use by domestication of wild varieties, selection and carrying out intensive breeding programs. It is also called SELECTIVE BREEDING. It is comparatively faster process where the effects are seen over a few



Some examples of artificial selection are to produce new breeds of dogs and cash crops like wheat and rice.


Speciation is the evolutionary process by which populations evolve to become distinct species.CHARLES DARWIN was the first to describe the role of natural selection in

speciation. It has been observed as a three-stage process: —


1. Isolation of populations.

2. Divergence in traits of separated populations (mating system and habitat



3. Reproductive Isolation of populations that maintains isolation when populations come into contact again.It occurs along two main pathways:-


(a) Geographic separation (Allopatric speciation).

(b) Through mechanisms that occurs within a shared habitat.(Sympatric speciation)





I. Multiple choice questions:


1. Industrial melanism is an example of:-

(a) Neo Darwinism

(b) natural selection

(c) Mutation

(d) Neo Lamarckism


2. By the statement “Survival of the Fittest” Darwin meant that:

(a) The Strongest of all species survives

(b) The most intelligent of the species survive

(c) The cleverest of the species survive

(d) The species most adaptable to changes survives


3. The diversity in the type of beaks 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


4. The Ship used by Charles Darwin during his sea voyages was:-

(a) HMS Beagle

(b) HSM Beagle

(c) HMS Eagle

(d) HSM Eagle


5. Which of the following is most important for speciation:-

(a) Seasonal isolation

(b) Reproductive Isolation

(c) Behavioral isolation

(d) Tropical isolation.


ll. Fill Ups:

a) The increase in dark population of moths was due to

b) The theory of natural selection was given by

c) HMS Beagle was sailed to the islands.


lll. True/False.

(a) Natural selection — nature made and Artificial Selection - Man Made

(b) Light coloured peppered moth is Biston carbonana and dark coloured peppered

moth is Biston betularia.


|. MCQ’s

1. b-Natural Selection: (Dark colour of peppered moth allows them to blend in

with their surroundings. This is because; pollution kills Lichens leaving tree



2. d- The species most adaptable to changes survives: (The organisms which are provided with favorable variations would survive because they are the fittest to face their surroundings while the unfit are eliminated).


3. C- Origin of species by natural selection: (Ancestral finches on reaching different Islands of Galapagos occupied all empty ecological niches in the absence of competition & evolved into different species).


4. a-HMS Beagle: (In 1831 Charles Darwin got an opportunity to travel on HMS Beagle ship for a voyage world exploration).


5. b-Reproductive Isolation: (Reproductive Isolation is most important factor

because it prevents the inbreeding between individuals of two different species).


ll. Fill Ups:

a) Industrial Melanism

b) Charles Darwin

c) Galapagos

lll. True/False:

a) True

b) False (Light coloured Biston betularia, Dark Coloured Biston carbonara )



1. Explain industrial melanism with example.

2. What do you understand by antibiotic resistance observed in bacteria in light

of Darwinian selection theory?



1. (a) What is the role of Darwin in explaining natural selection?

(b) Define speciation. write its types.





During the course of evolution different animal species evolved special organs

for a successful life like, wings in insects, birds and bats for flying, claws for

holding, burrowing and climbing in rats and squirrels and fins or paddles in aquatic

life for swimming. Similarly, most significant event in human evolution has been

evolution of brain which enabled him to become most superior member of animal

kingdom. The large and more complex brain evolved greater ability of thinking,

logical power and capacity of taking decisions depending on the situation.

Human evolution is the evolutionary process within the history of primates that

led to the emergence of Homo sapiens. This process involved the gradual

development of —


Size of Brain




Being Terrestrial


Linguistic skills


Present human species is named as Homo sapiens sapiens (Sapient =wise). T. H. Huxley (1863) in his book ‘Man's Place in Nature’ made first attempt to explain scientific grounds of upbringing of man. Charles Darwin (1871) in his book ‘The Descent of Man’ gave his ideas about ancestry of man.


The vertebrates of class mammalia as well as other primates have common ancestory with monkeys and apes. Mammals evolved from

primitive reptiles in early Jurassic period (about 210 million years ago).


Humans belong to family hominidae in which Homo sapiens is the only living species. The evolutionary history of man has been built up on the basis of study of fossils and molecular homology.


The’ earliest hominid stock included fossils of Dryopithecus,Ramapithecus or Sivapithecus unearthed from Africa and Asia.


Several species belonging to genus Homo can be recognised from fossil record. Human evolution took place in Africa and Asia.


Acommon ancestory for great apes and man has been deduced on the basis of similarities in DNA content, chromosome number and banding

pattern of chromosomes.


THE EVOLUTION OF HUMANKIND:Discoveries of remains of earliest ancestors and races give an idea of the process of human evolution.

The major forms, as recorded until date, are as follows:

The remains of these hominids Australopithecus, Zinjanthropus, etc.) were

discovered in Mid-Pleistocene or earlier in Transvaal, South Africa in 1925 and

Olduvai Gorge Tanganyika in 1959. A wide range of skulls and some skeletal parts

have been discovered.


They bear the following characteristics:

1. The skulls are smaller in size than that of modern man.

2. The volume of the brain ranged between 600-700 c.c.

3. The forehead was higher than in apes and the face was protruding.

4. The brow ridges were prominent.

5. The occipital condyles were ventrally placed and the rear part of the skull

was rounded.

6. The jaws were observed to be large with small incisors.4

7. It also had large and spatulate canines and large cheek teeth.




Fragmentary remains of Pithecanthropus erectus were discovered in the Mid-

Pleistocene of Solo River near Trimil, Java from 1891 until 1945.The features are:

1. A flattish-topped skull and projected behind.

2. The brow ridges were solid above the orbits.

3. The brain volume was between 775-900 c.c.

4. The imprint of the brain indicated the ability of speech.

5. The jaws were protruding with teeth arranged in an even curve.



The remains of skulls and parts of the skeletal structure of Pithecanthropus

(Sinanthropus) pekinensis were discovered up to 1943 from the Mid-Pleistocene

caves at Choukoutien (South-west of Peking), China.


The noted features are:

1. The skull was small and the brain volume was 850-1300 c.c.

2. The skull was low-vaulted.

3. The brow ridges were stout.

4. The imprint of the brain suggested the ability of speech.

5. Signs of implements of quartz and other rocks have been discovered.

6. The hearths showed the use of fire.



The remains of the transitional man were discovered in the Pleistocene bed of East

Africa. They were the makers of crudely chipped stone tools. This species of the

human race represents an intermediate stage between the Australopithecus and

Pithecanthropus erectus.The mean capacity of the brain was 680 c.c.



One lower jaw of Homo heidelbergensis was discovered in 1907 in a sandpit at

Mauer near Heidelberg (Germany). The remains were of the Mid-Pleistocene period. The jaw was massive with very broad ascending ramus which indicates,they had powerful jaw muscles. There was no chin. They also had stout teeth and the canines were not enlarged. Associated tools were not found.



The remains of the Neanderthal man from the late Pleistocene bed (before or during first Ice Age) were first discovered in Spain and North Africa to Ethiopia,Mesopotamia., Gibraltar, Neanderthal Valley near Dusseldorf (Germany), Southern Russia from 1848-1861.

The features of the Neanderthal man are:


Massive long and flat-topped skull.


The forehead was receding with heavy brow ridges.


The nose was broad.


The orbits were large.


The average brain volume was 1450 c.c.


The jaws were protruding but the chin was receding and they had large teeth.


The attachment sites of the occipital region of the skull and the cervical vertebrae indicate the existence of powerful neck muscles.


The females were shorter than males.


The Neanderthal man lived in caves and rock shelters made with stone.


Stone tools and weapons were used.


There was also evidence of the use of fire.


The period is estimated around 100,000 years ago.



CRO-MAGNON MAN (Homo sapiens fossilis):


These lived during last 30,000 years or more in Europe. These succeeded Neanderthals and became extinct about 10,000 years ago in the last glacial period.


These were about 180 cm. in height with a large skull, broad face, rounded

forehead, narrow nose and a prominent chin.


They lacked eyebrow ridges.


The cranial cavity was about 1660 c.c.


These were cave dwelling and hunters.


They made tools from stones and ornaments from ivory.


i.Cro—Magnon had perfectly orthognathus face.


ii. Cro—Magnon is the most recent ancestor of “Homo sapiens”.


iii. Cro—Magnon man was expert in making tools, weapons, paintings etc.

iv. Cranial capacity of modern man is 1350-5000 cm’.


MODERN MAN (Homo sapiens sapiens).

After last glacial periodie., about 10,000-75000 years ago, Homo Sapiens—sapiens appeared and began to spread all over the globe.


He learned to cultivate plants and domesticate animals of economic importance.


Skull is dome shaped. Cranial capacity is about 1400c.c.


These were the first settlers who started living a settled life.


Pre historic cave art came into existence 18000 years ago.


The shift to agriculture was around 10,000 years back leading to settled life style of human beings.





 1) When were Dryopithecus found on this earth?

(a) 50 million years ago

(b) 30 million years ago

(c) 15 million years ago

(d) 100 million years ago


2) Where did Australopithecines live?

(a) East African grasslands

(b) Central Asia

(c) Europe

(d) East Asia


3) Homo habilis is name for-

(a) Dryopithecus

(b) Austalopithecus

(c) Ramapithecus

(d) Neanderthal


4) Where were fossils of Neanderthal found?

(a) India

(b) North America

(c) Tanzania

(d) Java


5) When do Homo sapiens appeared on this earth?

(a) 75000 years ago

(b) 18,000 years ago

(c) 10,000 years ago

(d) none of these



1) The dryopithecus were hairy and walked like gorillas.

2) The brain capacity of Austraopithecines was 650-800cc.

3) Agriculture came around 18,000 years back.



1) Dryopithecus was more like_

2) Neanderthalused__ to protect their body.



1) (c) 15 million years ago

2) (a) East African grasslands

3) (b) Australopithecines

4) (d) Java

5) (a) 75,000 years ago The modern man Homo sapiens came into existence around 75,000 years to 10,000 years back.



1) True

2) True

3) False Pre historic cave art developed around 18,0000 years ago whereas

agricuture was started around 10,000 years back.



1) Ape

2) Hides



1) Write salient features of Australopithecines.

2) How would you describe Neanderthal man?

3) Name the various stages in evolution of man.



1) Write the salient features of Homo sapiens.








History of life comprises two events first, the origin of life and second the mechanism involved in the changes of living organisms through time or evolution of life.


Earth has originated about 4600 million years ago.


Life was present on earth about 3.9 billion years ago.


According to special creation theory, life is immutable and has never changed even since its origin.


Cosmozoic theory states that life originated from non-living matter.


Oparin and Haldane “theory of life origin” generally accepted.


Miller and Urey recreated conditions of primitive earth in the laboratory and

abiotically synthesized amino acids and nitrogen bases.


First formed cells are EOBIONTS.




The types of evolution which supports organic evolution are morphological,anatomical, embryological, paleontological, bio geographical, physiological and biochemical.


Morphological and anatomical evidences include homologous organs,analogous organs, vestigial organs and similar vestigial organs.


Paleontological study supports the theory of evolution and provides direct evidence.


Embryological evidences include similar early development, similar vertebrate embryo, recapitulation theory and development of certain organs.



Jean Baptiste Lamarck proposed the theory of evolution of inheritance of acquired characters or theory of use and disuse of organs.


Charles Darwin and Alfred Wallace in the mid nineteenth century introduced the principle of natural selection as mechanism of evolution.


Mutation theory of evolution was proposed by Hugo De Vries and is able to explain some of the drawbacks of Darwin's theory.


Neo-Darwinism is modified version of natural selection and is reconciliation between Darwinism and Mutation theory.


The modern theory of evolution stresses upon the importance of population as units of evolution and the central role of evolution of natural selection as the most important mechanism of the evolution.


Man belongs to class Mammalia of subphylum Vertebrata of phylum Chordata.


Linnaeus gave the name Homo sapiens to man.


Man is placed in order primata along with monkeys and apes.


Human evolution took place in Africa and Asia


Earliest hominid stock included fossils of Ramapithecus and Sivapithecus.


Homology is based on divergent evolution whereas analogy refers to convergent evolution.


Fossils recovered in Java revealed Horno erectus stage about 1.5 million years



During ice age between 75000 to 100000 years ago modern Homo sapiens arose. Pre historic cave art developed about 18000 years ago.


Hardy-Weinberg principal states that allelic frequencies in a population are stable and constant from generation to generation. The gene pool remains constant, it is termed genetic equilibrium.



Dear students, now let us do NCERT exercise questions:


Q.1: Explain antibiotic resistance observed in light of Darwanian selection theory.

Ans: Antibiotic was considered to be very effective against disease causing

bacteria. But within two or three years of introduction of antibiotic, new antibiotic

resistant bacteria appeared in population.

Sometimes the bacterial population happens to contain one or a few bacteria having mutations or in built variations which make them resistant to antibiotic. Such resistant bacteria survive and multiply quickly as the compete ting bacteria have died. Soon the resistance providing genes become wide spread and entire bacterial population become resistant.Antibiotic resistance may be achieved with in a week as bacteria have

generation of only 20 minutes.


Q. 2: Find from newspapers from popular science articles any few fossil discoveries or controversies about evolution.

Ans: Fossils of Dinosaurs have been unearthed to reveal evolution of reptiles in

Jurassic period. It further leads to evolution of birds and mammals. Recently,

fossils of shark toothed reptiles from Sahara deserts have been discovered.Fossils of flying birds with teeth in jaws have been discovered.


Q.3: Attempt giving a clear definition of the term species.

Ans: The members of a species resemble structurally and functionally and are able to interbreed freely and produce fertile off springs of their own kind and share a common gene pool.


Q 4: Try to trace the components of human evolution.

Ans: During human evolution ancestral human types had undergone a number of

remarkable changes in their brain size (cranial cavity), skeletal features, dietary

preferences etc. as shown in the table given in the text and in the following table:


Q 5: Find out through internet and popular science articles whether animals other than man have self-consciousness.

Ans: Yes, the apes like human beings have well developed facial muscles for showing facial expressions and have property of self-consciousness.


Q 6: List a few modern day animals and from internet link to corresponding ancient fossils. Name both.

Ans: Table


Q 7: Practise drawing various animals and plants.

Ans: Try it yourself.


Q 8: Describe one example of adaptive radiations.


What is divergent evolution? Give example.

Ans: It is the process of divergent evolution in which members of SAME ancestral

species of large taxonomic group are evolved along different lines in different

habitats of same geographical area.

Example: Darwin’s finches’ are an example of adaptive radiation.There are many varieties of small black birds in the Galapagos Islands. Darwin reasoned that after originating from a common seed eating stock, the finches must have radiate to different geographical locations in the same island and

undergone adaptive changes, especially in the type of beak. Living in isolation for

long, the new kind of finches emerged that could survive and function in the new



Q 9: Can we call human evolution as adaptive radiation?

Ans: No, we cannot call human evolution as adaptive radiation. It is the case of

descent with modification in which more advanced types are evolved from simple

forms. In case of human evolution there appear to be parallel evolution of human

brain and language.


Q 10: Using internet and discussing with your teacher, trace the evolutionary stages of any one animal say, horse.

Ans: The major evolutionary trend of horse:

i) General increase in size.

ii) Progressive loss of toes.

iii) Lengthening of toes that are retained

iv) Lengthening of limbs in general.

v) Enlargement of brain.

vi) Increase in height.

vii) Increase in the complexity of molar teeth and enlargement of last two and

eventually, the last three pre molars until they came to resemble molars.




Universe is around 20 billion years old and comprise of huge clusters of


The origin of universe is explained by the big bang theory.


Earth was formed 4.5 billion years back.


Life appeared 500 million years after formation of earth.

Different theories were given to explain the origin of life.

1. Theory of special creation: - According to this theory God Created life by his

divine art of creation.

2. Theory of Panspermia / Cosmozic Theory: - According to early greek thinkers

units of life called spores or Panspermia came from outer space and developed

into living forms.

3. Theory of spontaneous generation: - According to this theory, life originated

from decaying and rotting matter like straw an mud etc.Louis Pausteur dismissed the theory of spontaneous generation and

demonstrated that life came from pre-existing life.

4. Theory of Chemical evolution or Oparin- Haldane Theory:- This theory was

given by Oparin and Haldane and stated that life originated from pre-existing

non leaving organic molecules (e.g RNA, proteins etc)


1. Paleontological evidences:The study of fossil called palaeontology.

Fossils are remains of impression of past organism preserved in sedimentary rocks or other media.

Different aged rock sediments in earth crust indicate the presence of fossils

of different life forms which died during the sediment formation.

2. Morphological and Comparative anatomical evidences:The phylogenetic history can be revealed by comparative study of external and

internal structure.The organ with same structural design and origin but different functions is called homologous organs. e.g the forelimbs of some animals like whales,

bats and cheetah have similar anatomical structure of fore arms i.e humerus, radius, ulna, carpals, metacarpals and phalanges but they perform different functions.

Due to different needs some structures developed differently. This is called

divergent evolution.

The organs which are anatomically different but functionally similar are called analogous organs. e.g wings of butterfly and birds.

Due to same functions different structure evolved similarly. This is called

convergent evolution. Examples include; eye of octopus and mammals,flippers of penguins and dolphins, sweet potato and potato.

3. Embroyological evidences:-Embroyological support for evolution was also purposed by Ernst Haeckel based upon the observation of certain feature during embryonic stage common to all vertebrates that are absent in adult. The comparative study of embryos of various

animals is as follows:-

a) Similar development: - In all multicellular animals the fertilized egg i.e zygote undergoes cleavage producing blastula further changes into either two or

three layered gastrula. The animals having two layered gastrula are said to be

diploblastic. The animals with three layered gastrula are called triploblastic.Such a similar early development establishes a closed relationship among all multicellular animals.

b) Resemblence among vertebrate embryos:- Early stage of embryos development such as fish, salamander, tortoise, chick and aman, Itis obeserved that they resemble one another closely.

c) Resemblences among invertebrates larvae:- Annelids and Molluscs posses a similar type of larvae called trocophore and hemichordates also have similar larvae.

d) Biogenetic law/ Recapitulation theory:-Von Baer purposed law which is stated that during embroyonic development, the generalised features such as brain, aortic arches etc are common to all vertibrats, appered earlier then the special feature which distinguish the various members of the group

4. Adaptive Radiation:-It is the evolutionary process in which different species starting from a common point in a geographical area radiate to other geographical areas.

Within the Australian continent many different marsupials or pouched animals

are same as these have evolved from a common ancestral stock.

Darwin Theory:- Darwinsm in a theory purposed by Charles Robert Darwin. It states that organic evolution occurs through Natural Selection. It is also called Theory of Natural Selection. The main postulates of Darwin’s Theory of evolution are:

1. Rapid multiplication: - The population tends to multiply geometrically and the reproductive power of living organisms are much more than required maintaining their number.

2. Limited food and space: - It states that though a population tends to increase

geometrically and the food increases arithmetically so, two main limiting factors

i.e limited food and space does not allow a population to grow indefinitely.

3. Struggle for existence: - There is rapid multiplication of population where as

food and space is limited. This starts and everlasting competition between living

organisms for the basic needs of life like food, space, mate etc.

4. Variations: - According to it, no two individuals are identical except identical twins. Variation occurs in all organisms.

5. Natural selection or survival of fittest: Nature selects only those individuals

out of the population which are useful and best adopted to the environment.Another individuals are eliminated by it. This type or reduction of individuals by nature was called natural selection by Darwin and survival of fittest by Wallace.


This was put forward by Hugo de Vries based on his work.According to him evolution is caused by sudden large differences in the population.i.e mutation and not the miner variation as per Darwin.He believed that mutation caused speciation and called it single step large mutation.

MODERN CONCEPT OF EVOLUTION  - There are four factors in this concept.

1. Genetic variation in population:- Evolution occurs through the accumulation

of genetic variation in population over long period of time.

2. Natural Selection:- It means differential reproduction i.e some members of a

population have gene which enable them to grow up and reproduce at a higher rate and leave more surviving offspring in the next generation then others.

3. Speciation:- When environmental conditions change, a section of the population migrate to new area with different environmental conditions. New speciation may arise. This origin of new species from the existing one called Speciation.

4. Re-productive lsolation:- Isolation preserve the Integrity of a species by

checking by hybridisation.

HARDY- WEINBURG PRINCIPLE:This principle states that Allelic Frequencies in a population are stable and remains constant from generation to generation i.e., gene pool (Total number of genes and their alleles in a population) is constant. This is called genetic equilibrium or Hardy Weinberg equilibrium.It can be expressed as p°+2pq+q°=1 where p and q are frequencies of different alleles.Disturbances in genetic equilibrium results in evolution.

Dear students now let us try to discuss some more questions, other than NCERT exercise questions, from the chapter.


Q. 1. What are major theories of origin of life?

Ans: Major theories for the origin of life are:

i) Theory of special creation.

ii) Theory of spontaneous generation.

iii)Theory of catastrophism.

iv)Cosmozoic theory.

v) Theory of eternity of life.

vi) Modern or Oparin and Haldane theory


Q. 2. What are vestigial organs? Give two examples of vestigial organs in man?

Ans. Vestigial organs: The organs which occur in the reduced form and useless to the possessor are called vestigial organs. These organs are functional in related animals or ancestors. e.g. Muscles in pinna, Tail Bone in human body, Canines and Wisdom Teeth, Vermiform Appendix.


Q. 3. Define atavism. Give an example.

Ans: Atavism is the re-appearance of certain ancestral but nor parental structure

which have either completely disappeared or greatly reduced in the present 

generation. Atavism also called reversion or throw back.

e.g., Occurance of short tail in some babies and presence of additional mammae

in man.


Q.4. What are connecting links? Give at least two examples in support of your answer.

Ans: Connecting links. The living organisms, which possess characters of two different groups of organisms are known as connecting links e.g.


i) Euglena (a Protist is often regarded as a connecting link between plants and

animals. Its plants characters are presence of chloroplast and photoautotrophic nutrition. Its animal features include contractile vacuoles,mouth and binary fission.


ii)Penpatus ( Itis a caterpillar like arthropod which forms a connecting link

between annelida and arthropoda.


Q. 5. What are missing links? Give examples.

Ans: The fossil organisms, which show characters of two different groups of

animals are called missing links. e.g., Archaeopteryx. It shows the characters of

reptiles and birds.


Q. 6. Discuss recapitulation theory.

Ans. This theory is given by Ernst Haeckel in 1866. It states that an animal in its

individual development from egg to adult repeats or recapitulate in a condensed

form, the stages through which its ancestors have passed in course of their evolution. It is also known as “Ontogeny repeats phylogeny”. Ontogeny is the life history of individual animal; Phylogeny is the evolutionary history of the race of the

animal. This means an organism repeats its ancestral history during its development.


Q. 7. What is genetic drift?

Ans. The elimination of genes of certain traits wnen a section of population

migrates on the ease of a natural calamity. It alters the gene frequency of the

remaining population. The bottle neck effect and the founder effect are the results

of Genetic Drift.


Q. 8. What are fossils? How these are formed? Suggest the method of their age determination.

Ans: Preserve the traces of plants and animals formed the fossils. During the

formation of sedimentary rocks, the dead animals of sea and the land carried to

sea sink-down and get buried in the rocks. This cut-off oxygen condition that

prevent decay. The animals thus preserved in rocks have formed fossils. Age of a

fossil is computed by absolute dating method invoving either Uranium led technique of Carbon (C14) dating technique or Potassium- Argon technique.


Q. 9. What is Bottleneck effect?

Ans : When the population is at decline, the number of individual may reduce to the

extent that the small group of population constituting the population becomes

isolated and restricted in distribution.

These are then exposed to random genetic   drift resulting in fixation of certain genes. Such reduction in allele frequencies is called a genetic bottle-neck effect.

It prevents the species from extinction.


Q. 10. How mosquitoes become resistant to pesticides?

Ans : Mosquitoes spread diseases such as Malaria and Filaria besides infecting

irritating bites. They were originally sensitive to DDT, which killed them. Now they

have become resistant to DDT, Some individuals, even in the original mosquito

population were resistant to DDT. These DDT resistant mosquitoes were fewer because they had no advantage over the DDT sensitive, mosquitoes wnen DDT was not being used to control them. When the use of DDT, started, only the DDT resistant mosquitoes were able to survive and reproduce. Their resistant genotype in due course of time spread to almost the entire mosquito population. This made DDT, ineffective against them.

Chapter 7 Evolution