evolution

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Origin of Life

and

Evolution

Gurudatta K Wagh

Charles Robert Darwin FRS

12 February 1809 - 19 April 1882

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Darwin

- Established that all species of life

have descended over a time from

common ancestors

- Proposed the scientific theory that this

branching pattern of evolution resulted

from a process that he called natural

selection

- 'On the Origin of Species' (1859)

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Darwin's theory of natural selection

Only the fittest survive. Plants and

animals which are not fit die. Fit

species reproduce and pass on the

relevant characteristics to the

following generation which in turn

would make them fit for survival.

Natural selection - The process of

selection of characteristics that

contributes to the fitness for survival.

Rule of the nature - Organisms which

cannot adjust to their surrounding

have no right to survive

Selection of variants by

environmental factors forms the

basis for evolutionary processes

The "Evolution of Life" (organic

evolution) is the most widely

accepted theory 4

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Life on earth

A life-substance appeared on the

earth in sea water. It developed into

a unicellular form of life. Gradual

and orderly changes took place in

this unicellular form and it

developed into multicellular forms of

greater and greater complexity over

a prolonged period of nearly 300

crore years.

Evidence for organic evolution

Processes like growth, reproduction and

metabolism are essentially the same in all

organisms.

Analogous: Organs that are

fundamentally unlike except in function

a) Tail fin of lobster and flukes of whale

b) Wings of fly and wings of a bird

c) Eyes of arthropods and vertebrates

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Homologous: Organs which are

fundamentally the same in structure,

but perhaps modified for widely

different functions

a) The forelimbs of man (adapted for

handling), bat and bird (adapted for

flying), Whale and seal (adapted for

swimming) have the same principal

skeletal composition

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b) The scales of an ovulate pine cone

correspond with the carpels of a

flower and the scales of the staminate

cone correspond with the stamens of

a flower

Similarities observed between the

homologous organs are due to the

fact that evolution leads to modify the

existing structures for new modified

functions creating a new structure

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Vestigial organs (functionless in the

course of evolution)

The same organ may be functional in

one organism but vestigial in another.

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Vermiform appendix of man: Human

ancestors ate uncooked food with

considerable cellulose content in

them. The normal function of caecum

and appendix in mammals is the

digestion of cellulose.

Other examples are ear muscles,

wisdom teeth, plica semilunaris

(representing nictitating membrane of

the eye), coccyx (reduced tail) etc.

Monotropa uniflora. Indian pipe plant

is parasitic. Leaves are scale-like,

without chlorophyll. 11

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Palaeontological evidence

The process of fossilization takes a

very long period of time.

In order to study the fossil, the land is

excavated. The deepest layers have

fossils of invertebrates. In layers above

them are found prehistoric fish-like

animals, amphibians, reptiles, birds

and mammals respectively in that

order.

Connecting Links

Organisms referred to as 'connecting

links' are those which are structurally

intermediate between two different

groups. Connecting links can be found

among organisms that are still living.

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Duck-billed platypus

Lays eggs like reptiles

Has hair and mammary

glands like mammals.

'Peripatus' has

segmental nephridia,

thin cuticle and

parapodia - like

appendages as in

Annelida. At the same

time it has trachea and

open circulation as in

Arthropoda.

Lung fish though

a fish breathes air

through its lungs.

These organisms point strongly to the

fact that Mammals have evolved from

Reptiles and Amphibia from fishes. 16

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Embryological evidence

Embryology - study of development of an

organism from an embryo.

Comparative study of embryos of

different generation of vertebrates

exhibits that the embryos in their early

stages of development show a great deal

of similarities, but differ in the later stages

of development - suggesting common

ancestry for these animals.

Natural selection

After several generations the adapted

individuals may also be very different

from the original species.

Criterion for the natural selection

Successful adaptation for growth and

reproduction in the given environment.

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Industrial revolution

and the

Birmingham moths

Typica and carbonaria morphs on the

same tree. The light-coloured

typica (below the bark's scar) is nearly

invisible on this pollution-free

tree, camouflaging it from predators.

Biston betularia f. typica, the

white-bodied peppered moth

Biston betularia f. carbonaria,

the black-bodied peppered

moth

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As a result of industrial revolution,

there was an increase in the level

of pollution. Owing to this, there

was hardly any growth of algae or

fungi on the tree trunks.

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Instead, the tree trunks got covered by soot which gave

them a black colour. Now, it were the black moths that

began to get protection and the grey ones were easily

detected by their predators and consumed by them.

Nowadays in the surroundings of Birmingham black

moths are found in large numbers.

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How an individual plant or animal

acquired factors that made it better

adapted to its surroundings?

This was answered by the discovery of

the laws governing heredity and

mutation and thus Darwin's theory

came to be universally accepted.

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Please click the link in the next slide

Theory of Evolution

https://www.youtube.com/watch?v=p

Qp2lFcDEbw

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Thank you

• Viewers

• Std X text book MSBSHE

Government of Maharashtra

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• YouTube

• Wikipedia

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evolution

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