This document discusses several theories of evolution including: 1. Lamarck's theory of inheritance of acquired characteristics which was later disproven. 2. Darwin's theory of natural selection, where organisms with favorable variations are more likely to survive and reproduce. 3. De Vries' mutation theory, where sudden variations occur that can be inherited. 4. The modern synthesis combining genetics, mutation, natural selection and evidence from fields like biogeography, paleontology and embryology.

2. 1. Lamarck’s theory.
2. Darwin’s theory of natural selection.
3. Mutation theory.
4. Modern synthetic theory.
5. Evolution by anthropogenic source.
6. Adaptive radiation.

3. Lamarck was 1st to postulate the theory of evolution in his
book Philosophie Zoologique in 1809 .
The 2 principles of lamarck’s theory are
1. The theory of use and disuse
(i) Organs that are use often will increase in size.
Eg. Neck in giraffe (use)
(ii) Organs that are not used will degenerate.
Eg. Absence of limbs in snakes . (Disuse)

4. 2 . The theory of inheritance of acquired
characters :
Character that are developed during lifetime
of an organism are called as acquired
characters .
Acquired characters are inherited .

5. Disproved by August Weismann by
conducting experiments on mice for 20
generations by cutting their tail and
breeding them.
Weizmann proved that change in
somatoplasm will not be transferred to next
generation but change in germplasm will be
inheritance.

6.  Charles Darwin explained the theory of evolution in his book The
Origin Of Species By Natural Selection.
 He proved that fittest organisms can survive and leave more
progenies than the unfit ones through natural selection .
Darwin’s theory was based on several facts , Observation and
influences .
They are
1. Over production or prodigality of production..
2. Struggle for existence .
3. Universal occurrence of variation.

7.  All living organisms increase their population in larger
number .
Eg. 1.
Salmon fish produces about 28 million eggs during breeding
season , if all of them hatch , the sea would be filled with salmon
in few generations
Eg. 2.
Elephant, the slowest breeder that can produce only 6 young
ones in it’s life time can produce 6 million descendants at the
end of 750 years .

8.  Organisms struggle for food ,space and mate .
 Limiting factors – competition exist among members of the
population.
Darwin denoted struggle for existence in 3 ways
1. Inta specific struggle – between same species for food , space and
mate.
2. Inter specific struggle – with different species for food and space.
3. Struggle with environment to cope with climate variations , flood
,earthquake, drought ,etc.,

9. No two individuals are alike .
They are variations even in identical twins.
Even children born of same parents differ in colour
,height , behaviour ,etc.,
The useful variations found in an organism help
them to overcome struggle and variations are
passed on to the next generation.

10. According to Darwin, nature is the most powerful
selective force .
He compared origin of species by natural selection
to a small isolated group.
Darwin believed that the struggle for existence
resulted in the survival of the fittest .
Such organisms become better adapted to changed
environment.

11. Darwin
 Failed to explain the mechanism of variation.
 Explains the survival of the fittest but not the arrival of the fittest.
 Focus on small fluctuating variations that are mostly non heritage.
 Did not distinguish between somatic and germinal variation.
 Could not explain the occurrence of vestigial organs (specialization
of some organs like large tusks in extinct mammoths , oversized
antlers in the extinct Irish deer , etc.,

12.  Hugo de vries put forth the Mutation theory .
 Mutation are sudden random changes that occur in an organism that is not
heritable .

13. Mutation or discontinuous variation are
transmitted to other generations.
In naturally breeding populations, mutations
occur from time to time.
There are no intermediate form, as they are fully
fledged .
They are strickly subjected to natural selection .

14. According to this theory
1. Gene mutations
2. Chromosomal mutations
3. Genetic recombination
4. Natural selections
5. Reproductive isolation are the 5 basic factors involved
in the process of organic evolution.

15. Gene mutation
 It refers to the changes in the
structure of the gene .
 It is also called as point
mutation.
 It alters the phenotype of an
organism and produce
variation in their offspring .
Chromosomal mutation
 It refers to change in the
structure of chromosomes due
to detection, addition ,
duplication , inversion or
translocation .
 This too alters the phenotype
of an organism and produce
variations in their off spring .

16. Genetic recommendation
It is due to crossing over
genes during meiosis
This brings about genetic
variation in the
individuals of the same
species and leads to
heritable variations.
Natural selection
It does not produce any
genetic variation but once
such variations occur it
favours some genetic
changes while rejecting
others.

17. Reproductive isolation
It helps in preventing inter breeding between
related organisms .

18.  Natural selection can be explained clearly through industrial melanism .
Industrial melanism is a classical case of natural selection exhibited by the
peppered moth ,Biston betularia .These were available in 2 colours ,white and
black. Before industrialisation peppered moth both white and black coloured were
common in England .Pre industrialisation witnessed white coloured background
of the Wall of the building hence the white coloured moths escaped from their
predators. Post industrialization, the trees trunks became dark die to smoke and
shoot let out from the industries. The black moths camouflaged on the dark side of
the trees and the White moths were easily identified by their Predators. Hence
the dark coloured mock population was selected and their number increased when
compared to the white mouth . Nature offered positive selection pressure to the
black coloured mouth .Organisms that can adapt will serve and produce more
progenies resulting in increase in population through natural selection.

19. Artificial selection is a byproduct of human exploitation of
forest , ocean and fisheries or the use of pesticides,
herbicides ir drugs .
For hundreds of years humans have selected various types
of dogs all of which are variant of single species of dog .
If human being can produce new variety in short period,
then nature with its vast resources and long duration can
easily produce new species by selection

20.  The evolutionary process which produces new species diverged from
a single ancestral form becomes adapted to newly invaded habit is
called adaptive radiation .
 Adaptive radiations are best exemplified in closely related groups
that have evolved in relatively short time.
 Darwin’s finches and Australian marsupials are the best examples
for adaptive radiation.
 When more than one adaptive radiation occurs in isolated
geographical area having the same structural in functional
similarity it is due to convergent evolution