BIOLOGY, EVOLUTION BIOLOGY HELPFUL FOR NEET/ GSET/ NET/ GPSC EXAMINATION

1. BIOLOGY
STD 12
CHAPTER 7
EVOLUTION
SANJAY SIDDHAPURA
M.Sc., B.Ed., GSET, GPSC
(Ph.D. continue)

2. ORIGIN OF LIFE
• Evolutionary Biology is the study of history of life forms on earth.
• Solar system - Sun with its nine planets - M V E M J S U N P. (V - Brightest planet).
Originated about 4.5 billion year ago.
• Huge clusters of galaxies comprise the universe.
• Galaxies contain stars and clouds of gas and dust.
• In the solar system of the milky way galaxy
• Considering the size of universe, earth is indeed a speck (a tiny spot).

3. Big-Bang Hypothesis of cosmic evolution
• According to Big-Bang Hypothesis of cosmic evolution cosmos or
universe originated about 20 billion years back.

4. THE EARTH
• (1) Originated about 4.5 billion year ago.
• (2) The Temperature of early earth was 5000-6000°C and without atmosphere.
• (3) The later conditions on earth were
• High temperature
• Volconic lava and volcanic storm
• Molten mass (Volcanic lava) covered the earth surface and it released CH4, NH3, CO2, Water
Vapour.
• All gases like H2, CH4, NH3 make primitive atmosphere reducing.

5. • (4) By the passing of time, earth rotating speed and temperature came
down (below 100°C) and hydrosphere formed after lithosphere and
atmosphere. The ozone layer was formed. As it cooled, the water vaporfell
as rain, to fill all the depressions and form oceans.
• Earth core – Contain heavy metals.
• Earth crust (Lithosphere) – Si, Na, K, Mg, Ca, P, F, Cl, Ag
• Atmosphere – H, He, Ar, N, O, C
• Hydrosphere – Hot boiling water
• Life appeared 500 million years after the formation of earth, i.e., almost four billion
years back.

6. ORIGIN OF LIFE ON EARTH
• (i) Cosmozoic theory
• Richter, Arrhenius, Hoyle.
• (1) It explains “eternity of life” means life was present since the origin of earth and will remain till earth
exists.
• (2) It also explains theory of panspermia means the life present in each and every star, planet, sattelite.
The spores of life continuously being transfered from one to another star, planet, sattelite in the form of
spores through meteorites.
• (3) Life had came from another star or planet of universe on Earth in the form of life spores (Pangenes)
through meteorites.
• (ii) Theory of Abiogenesis or spontaneous generation theory
• Given by some greek thinker like Aristotle, plato, Ampedocles “Life came out of decaying and rotting
of Non-living matters like straw and mud.”
• Supporter – Von Helmotnz

7. ORIGIN OF LIFE ON EARTH
• (iii) Theory of Biogenesis
• Harvey and Huxley - “New Life originates from pre-existing life”
• Biogenesis = Omnis Vivum ex ova or Vivo
• Supporter –
• (a) Louice pasture:
• Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life.
• He took swan necked flask contain ing boiled yeast and sugar. life did not come from killed
yeast.
• while in another flask open to air, new living organisms arose from ‘killed yeast’.
• But Spontaneous generation theory was dismissed once and for all.

8. ORIGIN OF LIFE ON EARTH
• (iv) Theory of special creation:
• Father swarez
• Super natural power created this living nature or Divine creation of one or more superior,
intelligent and all powerfull God, created all livings.
• (a) According to bible – God created this living nature with in 6 days –
• 1st Day – Earth and Heaven
• 2nd Day – Sky and Water
• 3rd Day – Land and Vegetation
• 4th Day – Moon and Stars
• 5th Day – Fishes and Birds
• 6th Day – Terrestrial animal and first human male Adam.
• Note: Eve (First human female) borne from 12th Rib of Adam.

9. ORIGIN OF LIFE ON EARTH
• (b) According to Hindu Epic – Brahma created this living nature.
• From Head of Brahma – Human, Devil, Angel
• From thorasic Region of Brahma – Birds
• From Mouth of Brahma – Goats
• From Hairs of Brahma – Other animals and Vegetation.
• Objection of special Creation Theory: It upholds that life is immutable and had not changed
ever since its origin.
• (v) Theory of Catastrophism or Sudden creation theory: G. Cuvier
• (1) G. Cuvier is the father of modern palaentology and according to him cataclism (Great
destruction) or Revolution or catastrophism (Disastrous event) occures upon earth from time to
time which Completely destroys all persisting living.
• (2) Then new organism suddenly formed from inorganic matter by crystalysation.

10. EVOLUTION OF LIFE FORMS – A THEORY
• Evolution is the formation of complex organisms through ‘change’ from simple ancestral
types over the course of geological time.
• It is through the constant process of evolution (since the origin of life) that has resulted into
enormous variety of plants and animals that have come to exist on this earth at present.
• Conventional religious literature tells us about the theory of special creation. This theory has
three connotations.
• One, that all living organisms (species or types) that we see, today were created as such.
• Two, that the diversity was always the same since creation and will be the same in future also.
• Three, that earth is about 4000 years old.
• All these ideas were strongly challenged during the nineteenth century.

11. • Based on observations made during a sea voyage in a sail ship called H.M.S. Beagle round the
world, Charles Darwin concluded that existing living forms share similarities to varying
degrees not only among themselves but also with life forms that existed millions of years
ago.
• Many such life forms do not exist any more.
• There had been extinctions of different life forms in the years gone by just as new forms of
life arose at different periods of history of earth.
• There has been gradual evolution of life forms.

12. • Any population has built in variation in characteristics. Those characteristics which enable
some to survive better in natural conditions (climate, food, physical factors, etc.) would
outbreed others that are less-endowed to survive under such natural conditions.
• Another word used is fitness of the individual or population.
• The fitness, according to Darwin, refers ultimately and only to reproductive fitness.
• Hence, those who are better fit in an environment, leave more progeny than others.
• These, therefore, will survive more and hence are selected by nature.
• He called it natural selection and implied it as a mechanism of evolution.
• Alfred Wallace, a naturalist who worked in Malay Archepelago had also come to similar
conclusions around the same time.

13. • All the existing life forms share similarities and share common ancestors. However, these
ancestors were present at different periods in the history of earth (epochs, periods and eras).
• The geological history of earth closely correlates with the biological history of earth.
• A common permissible conclusion is that earth is very old, not thousand of years as was
thought earlier but billions of years old.

14. WHAT ARE THE EVIDENCES FOR
EVOLUTION?
• 1. Palaeontological evidences
• 2. Morphological and anatomical evidences
• (a) Homologous organs and homology
• (b) Analogous organs and analogy
• 3. Adaptive radiation (Bio-geographical evidences)
• 4. Biochemical evidences
• 5. Embryological evidences
• 6. Evidences for evolution by natural selection

15. 1. PALAEONTOLOGICAL EVIDENCES
• Palaeontology is the study of fossils.
• Fossils are found in Sedimentary rock, polar snow, resin of plants.
• Fossils are the remains or traces of animal and plant life of the past, found embedded in rock
either as petrified hard parts or as moulds, casts or tracks.
• Fossils are written documents of evolution.
• Significance of fossils:
• To study phylogeny (evolutionary history or race history). E.g. Horse evolution.
• To study the connecting link between two groups of organisms. E.g. Archaeopteryx.
• To study about extinct animals. E.g. Dinosaurs
• To study about geological period by analysing fossils indifferent sedimentary rock layers. The
study showed that life forms varied over time and certain life forms are restricted to certain
geological time spans.

16. • Snow - Large body sized animal
• Resin - Small animal like insects.
• Petrified fossil – Only hard part of the body (teeth, bone, shell of
mollusc, skeletun of arthropod) present between layers of stratified rock.
• Printed fossil or moulded fossil – The print of animal or plant body in
stratified rocks. Ex. Archeopterix.
• Living fossil: Only existing representative of a group means all the member of a
group extincted but the only surviving member of that group is called Living fossil.
• Ex. – Limulus - King Crab (An Arthropod)
• Latimeria - Coelocanths (Bony Fish)

17. 2. MORPHOLOGICAL AND ANATOMICAL
EVIDENCES
• Comparative anatomy and morphology shows that different forms of animals have some
common structural features.
• (a) Homologous organs and homology
• Homologous organs are the organs having fundamental similarity in structure and origin
but different functions.
• This phenomenon is called Homology.
• The origin of homologous organs is due to Divergent evolution.
• Divergent evolution is the process by which related species become less similar in order to
survive and adapt indifferent environmental condition).
• Homology indicates common ancestry.

18. • E.g. Homology in animals
• Human hand, Whale’s flippers, Bat’s wing, and Cheetah’s foot.
• All these perform different functions, but are constructed on the same plan.
• humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs.

19. Homology in plants: E.g. Thorns of Bougainvillea and tendrils of
Cucurbita.
CHEETAH
TENDRILS

20. (b) Analogous organs and analogy
• Analogous organs are the organs having similar function but different structure and origin.
This phenomenon is called Analogy.
• Origin of analogous organs is due to Convergent evolution.
• Convergent evolution is the process by which unrelated species become more similar in order
to survive and adapt in similar environmental condition.
• Wings of insects (formed of a thin flap of chitin) and wings of birds (modified forelimbs).
• Eyes of Octopus (retina from skin) and mammals (retina from embryonic brain).
• Flipper of Penguins and Dolphins.
• Sweet potato (modified root) and Potato (modified stem).
• Trachea of insects (from ectoderm) and lungs of vertebrates (from endoderm).

22. 3. Adaptive radiation (Bio-geographical evidences)
• Adaptive radiation (evolution by adaptation) is the evolutionary process that produces new
species from a single, rapidly diversifying lineage. This process occurs due to natural
selection.
• An example of adaptive radiation is Darwin finches, found in Galapagos Island. A large
variety of finches is present in Galapagos Island that arose from a single species, which
reached this island accidently.
• As a result, many new species have evolved, diverged, and adapted to occupy new habitats.
• These finches have developed different eating habits and different types of beaks to suit their
feeding habits.

23. Adaptive radiation• EXAMPLE :-
• The insectivorous, blood sucking, and other species of finches with varied dietary habits
have evolved from a single seed eating finch ancestor.
• Australian marsupials. A number of marsupials each different from the other evolved
from an ancestral stock. But all within the Australian island continent.

24. • Placental mammals in Australia also exhibit
adaptive radiation in evolving into varieties of
such placental mammals each of which appears
to be ‘similar’ to a corresponding marsupial
(E.g. placental wolf and Tasmanian wolf-
marsupial).
• When more than one adaptive radiation appears
in an isolated geographical area, this leads to
convergent evolution. E.g. Australian
Marsupials and Placental mammals

25. 4. Biochemical evidences
• During development, all vertebrates have a
post-anal tail and paired pharyngeal pouches.
• Organisms that show similarities in their
embryonic development may have a common
ancestry.
5. Embryological evidences
• Similarities in proteins and genes performing a given function among diverse
organisms give clues to common ancestry.

26. 6. EVIDENCES FOR EVOLUTION BY NATURAL SELECTION
• Natural selection is the process by which the organisms that are best suited for their
environment survive and reproduce.
• E.g. Industrial melanism (In England)
• Before industrialization (1850s), it was observed that there were more whitewinged moths
(Biston betularia) on trees than darkwinged or melanised moths (Biston carbonaria).
• Reason: There were more white coloured lichens that covered the trees. Hence, white
winged moths were able to camouflage themselves and survived. But the dark coloured
moths were picked out by predators.
• After industrialization (1920), there were more dark winged moths and less white winged
moths.
• Reason: The tree trunks became dark due to industrial smoke and soot. Under this
condition the white winged moth did not survive as the predators could identify them easily.
However, dark winged moth survived because of suitable dark background.

28. • Excess use of herbicides, pesticides, antibiotics or drugs, etc.
resulted in selection of resistant varieties.
• This is known as natural selection by anthropogenic action.
• This also tells us that evolution is not a direct process in the sense of
determinism.
• It is a stochastic process based on chance events in nature and chance
mutation in the organisms.

29. THEORIES OF BIOLOGICAL EVOLUTION
• 1. Lamarckism (Theory of Inheritance of Acquired Characters)
• 2. Darwinism (Theory of Natural Selection)
1. LAMARCKISM (THEORY OF INHERITANCE OF ACQUIRED CHARACTERS)
• It was proposed by Lamarck.
• Principles of Lamarckism or Lamarckian theory were based on four theoretical aspects of
evolution of organisms.
• (i) Internal urge of organisms
• (ii) Environmental change and new needs
• (iii) Use and disuse of organs
• (iv) Inheritance of acquired character

30. • (i) Internal urge of organisms
• All the living things and their component parts are continually increased due to an urge or
internal force of life and due to an inherent ability of organism itself.
• (ii) Environmental change and new needs: Environment keeps on changing and thus,
influences the organism by creating new needs.
• The new needs are met with by producing new structures.
• Thus change in environment brings about the development of new characters which results
structural modifications and behavioral change in the organism, so that one organism develop
adaptive features to co-op with new environment.
• (iii) Use and disuse of organs: A constant use of an organ results in its better development
whereas disuse leads to its ultimate degeneration and loss.
• (iv) Inheritance of acquired character: The modifications produced during the whole life of
an organism the transferred to its offspring in the process of heredity.
• Therefore acquired characters are inherited leading to morphological and anatomical changes in a
species lead to be evolved.

31. • Thus Lamarckism holds the view that evolution taking place by the cumulative effect of
environment on organism in relation to heredity over a long period of time.
• E.g.
• Long neck of giraffe is due to continuous elongation of their neck to forage leaves on tall trees.
This acquired character was inherited to succeeding generations.
• Disappearance of limbs in snakes.

32. 2. Darwinism (Theory of Natural Selection)
• It was proposed by Charles Darwin.
• It is based on two key concepts: Branching descent and natural selection.
• The theory states that organic evolution occurs through natural selection and accumulation
of heritable variations that provide structural and functional superiority to some individual
over others in their survival and reproduction.
• The important features of the theory are as follows:
• (i) Over production: Every plant and animal has a tendency to produce in geometrical
progression (Malathian concept). Population size grows exponentially if everybody
reproduces maximally (E.g. bacterial population).
• (ii) Limited food and space: There is limitation of food and space of earth. Therefore,
populations of different species cannot increase beyond a certain limit.

33. 2. Darwinism (Theory of Natural Selection)
• (iii) Struggle for existence: The immense power of reproduction ensures a competition
among the offsprings for food, shelter, clothing, light, mating partner and all other necessities of
life. The competition is maximum amongst members of the same species. i.e. intraspecific
competition.
• (iv) Variations: The differences of offsprings from their same species are called variations.
These are the most important aspects of evolution. No two individuals were exactly alike. Such
variations were of two kinds, some were inheritable while others were not inheritable. Further,
the variation may be beneficial, harmful or neutral.
• (v) Survival of fittest: The organisms with useful variations have an upper hand in the struggle
for existence and they come out successful. They win the struggle, survive and propagate the
variation to the next generation. Others with harmful variations perish.
• (vi) Inheritance of useful variations: Individual with useful variations reproduces and
transfers the variations to the next generation. Next generation repeats the process of formation
of new variations and natural selection. There is therefore, a continuous selection.

34. • (vii) Natural selection: According to Darwin, nature selects the fittest ones to survive and
rejects the unfit ones. In nature, only those organisms which are best adapted to a given set
of conditions are most likely to survive. In this way, in species advantageous characters are
increasingly accumulation generation after generation and disadvantageous characters
gradually disappear.
• An E.g. of such selection is antibiotic resistance in bacteria. When bacterial population was
grown in an agar plate containing antibiotic penicillin, the colonies that were sensitive to
penicillin died, whereas one or few bacterial colonies that were resistant to penicillin survived.
• This is because these bacteria had undergone chance mutation, which resulted in the
evolution to penicillin drug.
• Hence, the resistant bacteria multiplied quickly as compared to non-resistant (sensitive)
bacteria, thereby increasing their number. Hence, the advantage of an individual over other
helps in the struggle for existence.
• (viii) Formation of new species: Accumulation of variations produces a completely new
species.

35. CRITICISM OF DARWINISM
• Darwin did not distinguish between somatic and germinal variations.
• Darwin explained the survival of fittest but not arrival of fittest.
• Natural selection operates on small variations, most of which are not heritable.
• Over specialisation of organs cannot be explained by natural selection.
• On the basis of these objections and other scientific researches it can be said that natural
selection is an important cause of variation but not its sole reason. “Recently the theory has
been modified and known as Neo-Darwinism.
• Neo-Darwinism or Modern synthetic theory is an integration of separate ideas on
evolution, and genetics.
• It is based on Mutations + natural selection + isolation.

36. MECHANISM OF EVOLUTION
• Darwin ignored about origin of variation and mechanism of speciation.
• Hugo de Vries proposed Mutation Theory of evolution.
• He conducted some experiments on Oenothera lamarckiana (evening primrose)
and believed that evolution takes place through mutation and not by minor variation.
Darwin’s theory Mutation theory
• Evolution is caused by minor variations. • It is the mutation which causes evolution.
• Darwinian variations are small, slow and
directional
• Mutations are random, sudden and
directionless
• Evolution for Darwin was gradual. • deVries believed mutation caused speciation
and hence called it saltation (single step
large mutation).

37. VARIATIONS
• Variations can be defined as the differences that occur in the characteristics between members
of the same species.
• Variations occur with reference to every character. In the absence of variations, every species
would have continued to exist in the same form and no new species would have arisen from
the existing one.
• Thus, variations are the raw materials for organic evolution.
• Variation and evolution: Variation helps the species to survive in all the conditions.
Environmental conditions such as heat, light, pests, and food availability can change suddenly
at only one place.
• At that time, only those variants resistant to these conditions would be able to survive.
• This will slowly lead to the evolution of a better adapted species.
• Thus, variation helps in the evolution of sexually reproducing organisms.

38. CAUSES OF VARIATION

39. SPECIATION
• Origin of a new species from the existing one due to reproductive isolation of a part of its
population is called speciation.
• It is an important aspect of evolutionary process.
• There are four geographical modes of speciation in nature:
• (i) Allopatric speciation (Geographical isolation)
• (ii) Peripatric speciation
• (iii) Parapatric speciation
• (iv) Sympatric speciation (reproductive isolation)

40. • (i) Allopatric speciation (Geographical isolation)
• Population splits into two geographically isolated regions and each population undergoes
genotypic and/or phenotypic divergence. E.g. Darwin finches.
• (ii) Peripatric speciation:
• New species are formed in isolated small peripheral population that are prevented from
exchanging genes with the main population. Genetic drift plays an important role here.
• (iii) Parapatric speciation
• Two populations are partially separated geographically, so individuals of each species may
come in contact with the other from time to tome but reduced fitness of the heterozygote
prevents breeding between the two species.
• (iv) Sympatric speciation (reproductive isolation)
• It refers to the formation of two or more descendents species from a single ancestral species
all occupying the same geographical location.

41. HARDY- WEINBERG PRINCIPLE
• “Under certain conditions of stability, allelic frequencies remain constant form generation to
generation in sexually reproducing organism”, proposed by two scientist hardy and Weinberg
and the law are called Hardy-Weinberg law.
• Hardy-Weinberg law is an algebraic equation that describes the genetic equilibrium within a
population.
• It states that in a large, random-mating population, the gene pool (total genes and their
alleles in a population) tends to remain constant from generation to generation unless outside
forces act to change it.
• In such a way even the rarest forms of genes, which one would assume would disappear, are
preserved.

42. • Hardy Weinberg principle assumes that, within a given population:
• (i) Mating is random. There is no mating preference. For example an AA male does not
prefer an aa female.
• (ii) No mutations are arising i.e. the alleles must not change.
• (iii) No gene flow i.e. Exchange of genes between the population and another population
must not occur.
• (iv) No natural selection. Natural selection must not favourany particular individual.
• (v) Population size is infinitely large. The population must be large to minimize random
sampling errors.

43. Importance
• Hardy-Weinberg law is only tree and applicable in following conditions –
• i. Population must be large (not small)
• ii. Must be random mating (not selective) and free gene flow
• iii. Mutation must occur
• iv. Gene flow, gene migration and genetic drift must be avoided.
• v. Hybridization and gene recombination must be avoided.
• The Hardy-Weinberg model enables us to compare a population’s actual genetic structure
over time with the genetic structure we would expect if the population were in Hardy-
Weinberg equilibrium (i.e., not evolving).
• If genotype frequencies differ from those we would expect under equilibrium, we can
assume that one or more of the model’s assumptions are being violated, and attempt to
determine which one (s).

44. Equation of Hardy and Weinberg law
• Consider a population whose gene pool contains the alleles A and a.
• Hardy and Weinberg assigned the letter p to the frequency of the dominant allele A and the
letter q to the frequency of the recessive allele a.
• Since the sum of all the alleles must equal 100%, then p + q = 1.
• They then reasoned that all the random possible combinations of the members of a
population would equal
(p+q) 2 or p2+ 2pq + q2.
• The overall equation for the Hardy-Weinberg equilibrium is expressed in this way:
p2 + 2pq + q2 = 1 [binomial expansion of (p+q)2].

45. FACTORS AFFECTING HARDY-WEINBERG EQUILIBRIUM
• (i) Gene migration: It is the gene flow from one population to another. When migrations
of a section of population to another place occur, gene frequencies change in the original as
well as in the new population. New genes/alleles are added to the new population and these
are lost from the old population.
• (ii) Gene flow: Gene migration that happens multiple times is termed as gene flow.
• (iii) Genetic drift (Sewall wright effect) : Genetic drift is the accidental gene flow causing
change in frequency. Sometimes, the change in frequency is so different in the new sample of
population that they become a different species. The original drifted population becomes
founders and the effect is called founder effect.
• (iv) Mutation: Mutations result in formation of new phenotypes. Over few generations, this
leads to speciation.
• (v) Genetic recombination: It is the reshuffling of gene combinations during crossing over
resulting in genetic variation.

46. • (vi) Natural selection:
• Natural selection is the process by which the organisms that are best suited for their
environment survive and reproduce.
• Natural selection is a process in which heritable variations enabling better survival are
enabled to reproduce and leave greater number of progeny.
• A critical analysis makes us believe that variation due to mutation or variation due to
recombination during gametogenesis, or due to gene flow or genetic drift results in changed
frequency of genes and alleles in future generation.
• Coupled to enhance reproductive success, natural selection makes it look like different
population.
• There are three kinds of natural selection.
• (i) Stabilizing selection (ii) Directional selection (iii) Disruptive selection

47. • (i) Stabilizing selection:
• In which more individuals acquire mean character value.
• Both extremes of the variation of a trait are eliminated.
• This selection results in favouring the average individuals in a population. This occurs when
the environment doesn’t change.
• Natural selection doesn’t have to cause change, and if an environment doesn’t change there is
no pressure for a well-adapted species to change.
• Fossils suggest that many species remain unchanged for long periods of geological time.
• One of the most stable environments on Earth is the deep ocean.

48. • (ii) Directional selection
• More individuals acquire value other than the mean character value.
• It is the selection that favours one of the extreme variations of a trait. This selection results
in a shift towards one extreme.
• This occurs whenever the environment changes in a particular way. There is therefore
selective pressure for species to change in response to the environmental change.
• E.g. The peppered moth, Bacterial resistance to antibiotics, Pesticide resistance.
Directional selection

49. • (iii) Disruptive selection:
• More individuals acquire peripheral character value at both ends of the distribution curve.
• It is the selection that favours both extremes of the phenotype. Hence, the Intermediate
phenotype is eliminated.
• This selection results in favouring either extreme of a trait’s variation.
• This occurs where an environment change may produce selection pressures that favour two
extremes of a characteristic.
Disruptive selection

50. A BRIEF ACCOUNT OF EVOLUTION
• A Trip through Geologic Time:
• By looking at fossils and by figuring out the age of rocks, scientists have come up with
something like a calendar of Earth’s history. This calendar is called the geologic time scale.
• The scale is divided into four sections called eras.
• Each era represents a very long period of time. The four eras are: Precambrian, Palaeozoic,
Mesozoic and Coenozoic.
• Each era is subdivided into periods. Scientists selected the divisions based on information from
fossils. Each division of the time scale is based on the kinds of organisms that lived during that
time. The fossil record also shows several times when a mass extinction took place. A mass
extinction is an event that happens when many organisms disappear from the fossil record at
the same time. The figure below shows the four eras of Earth’s geologic time scale.

51. A BRIEF ACCOUNT OF EVOLUTION

54. A BRIEF ACCOUNT OF EVOLUTION
• (1) Appearance of first cellular form of life on earth: Anaerobic Heterotrophic bacteria were
the first cellular form of life on earth, that originated about 3.5-3.2 billion year back. (According
to new NCERT 2000 million years back and made contradiction itself at two places in text book
so you are advised not to go with NCERT)
• Some of these cells had the ability to release O2. The reaction could have been similar to the
light reaction in photosynthesis where water is split with the help of solar energy captured and
channelised by appropriate light harvesting pigments. Slowly single-celled organisms became
multi-cellular life forms.
• (2) Appearance of invertebrates: By the time of 500 million year ago, Invertebrates formed
and active.
• (3) Appearance of first Vertebrates (Jawless fishes): Jaw less fishes evolved around 350 mya.
These fishes were flashy and lobed fined.
• Sea weeds and few plants existed probably around 320 mya. We are told that the first organisms
that invaded land were plants.

55. A BRIEF ACCOUNT OF EVOLUTION
• (4) Lobed fin fishes (Coelacanth) and origin of Amphibian: Fish with stout and strong
flashy lobed fins (coelacanth) could move on land and gave rise primitive amphibian and then
go back to water.
• (5) Coelacanth as living fossil: In 1938, a fish caught in South Africa was coelacanth which
was thought to be extinct but the reality is there are no specimens of flashy lobed fin fishes
except coelacanth (Lattimeria) with us hence called living fossil.
• (6) First life that migrated from aquatic to terrestrial habitat: Plants (Mass or Bryophytes)
• (7) Ancestor of Amphibia (Frogs and Salamanders): Lobbed fin fishes (coelacanth) are the
ancestor of amphibian likes frogs and salamanders.
• Amphibia were first animal but second organism (because first were plants) which migrated
from aquatic to terrestrial habitat.

56. A BRIEF ACCOUNT OF EVOLUTION
• (8) Origin of Reptiles and reason of their successful life: Reptiles originated from amphibian and
reptiles have thick shelled eggs which do not dry up in sun unlike those of amphibian, in next 200
million years or so. Reptiles of different shapes and sizes dominated on earth. Some of these land
reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g. Ichthyosaurs). The land
reptiles were, of course, the dinosaurs.
• Giant ferns (pteridophytes) were present but they all fell to form coal deposits slowly.
• Ex. 1. Turtle, Tortoise, Crocodiles.
• 2.Dinosaurs:
• i. Ichthyosaurs: Fish like and aquatic (200 mya)
• ii. Tyrannosaurus rex: Biggest dinosaur with 20 feet height and huge dagger like teeth.
• (9) Golden age of Reptiles extinction of Dinosaurs: Jurassic period was the golden age reptile and
About 65 mya, dinosaur an extincted because of two probable reasons –
• i. Climatic changes killed them
• ii. Most of them evolved in birds.
• The truth may live in between. Small sized reptiles of that era still exist today.

57. A BRIEF ACCOUNT OF EVOLUTION
• (10) Origin of Birds: Birds originated from reptiles and evidences comes from Archaeopteryx
(Connective link b/w reptiles and birds)
• (11) Origin of mammals and their domination upon others: Mammals also originated from reptiles
(therapsid) with separate line of birds. The first mammals were like shrews. Their fossils are small sized.
• Mammals dominated over others because of following reason.
• (i). They were viviparous and protected their unborn young inside the mother’s body.
• (ii) They (mammals) were mare intelligent in sensing and avoiding danger at least.
• When reptiles came down mammals took over this earth.
• There were in South America mammals resembling horse, hippopotamus, bear, rabbit, etc.
• Due to continental drift, when South America joined North America, these animals were overridden by
North American fauna. Due to the same continental drift pouched mammals of Australia survived
because of lack of competition from any other mammal. Some mammals live wholly in water. Whales,
dolphins, seals and sea cows are some examples.

58. A BRIEF ACCOUNT OF EVOLUTION
• (12) Mammals with interest of evolutionary history: Horse, elephant, dog with special stories
of evolution.
• (13) Most success full story of Human evolution: With language skills and self consciousness.
coelacanth
(Lattimeria)
Jaw less fish
Ichthyosaurs
Tyrannosaurus rex
shrew
therapsid

59. A BRIEF ACCOUNT OF EVOLUTION
• (12) Mammals with interest of evolutionary history: Horse, elephant, dog with special stories
of evolution.
• (13) Most success full story of Human evolution: With language skills and self consciousness.

60. ORIGIN AND EVOLUTION OF MAN

61. ORIGIN AND EVOLUTION OF MAN
• About 15 mya, primates called Dryopithecus and Ramapithecus
were existing. They were hairy and walked like gorillas and
chimpanzees.
• (1) Dryopithecus – Arose about 15 Million yr ago, more ape-
like, walked like Chimpanzee and Gorilla. It is supposed as
common ancestor of Ape and man.
• (2) Ramapithecus – Arose about 15 million yr ago, walked
like apes. It was more man-like hence called oldest human
ancestor and direct line towards human evolution.

62. ORIGIN AND EVOLUTION OF MAN
• (3) Few Hominids fossils of Ethiopia and Tanzania – Few fossils of man like
bones have been discov ered (excavated) in Ethiopia and Tanzania.
• These revealed hominid features leading to the belief that about 3-4 million yr ago,
man like primates walked in eastern Africa.
• Similarity and difference in fossil bones, possibly they were two types
• 1st type – Australopithecines
• They were Man like primates walked in east African grassland about 2 million yr ago.
• They were probably not taller than 4 feet but walked up right.
• Many evidences reflects that they hunted with stone weapons but essentially ate fruit
means hunting was their way to entertain and amusement but they actually were
vegetarian.
• 2nd type – Homo habilis
• It was first human being the hominid with 650-800 cc brain capacity.
• It was first tool maker or Handy man but after being hunter it probably did not eat
meat.

63. ORIGIN AND EVOLUTION OF MAN
• (6) Homo erectus –
• Fossils discovered in Java in 1891.
• About 1.5 million yr ago with cranial capacity
900 cc (Java ape man).
• Homo erectus used fire and probably eat meat.
• (7) Neanderthal-
• Arose about 1, 00,000 - 40,000 year back, near
east and central Asia.
• Cranial capacity-1400 cc
• Neanderthal used hides to protect their
domestic animals and himself.
• First burial funeral of their dead started by
Neanderthal.

64. ORIGIN AND EVOLUTION OF MAN
• (8) Homo sapiens-
• Arose during ice age between 75,000-10,000
year back near Caspian Sea.
• Prehistoric art- developed by Cro-Magnon
about 18,000 yr back.
• Homo sapiens sapiens developed in to three
races-
• White race
• Negroid race
• Mongoloid
• Agriculture and human settlements started
about 10,000 year back.

65. Thank you