this ppt traces the evolutionary history of humans and presents the description of evolution on the basis of various theories put forward by various eminent scientists

2. 1
• THEORY OF ORGANIC EVOLUTION -
LAMARKISM
2
• NEO-LAMARKISM
3
• THEORY OF NATURAL SELETION- DARWINISM
4 • NEO-DARWINISM
5 • MUTATION THEORY- HUGO- DE-VRIES
6 • MODERN SYNTHETIC THEORY

3. Given by JEAN BAPTISTE DE LAMARK IN 1802
Theory is also known as theory of “ACQUIRED CHARACTERS” or
“THEORY OF USE AND DISUSE OF ORGANS”
According to this theory the changes in structure or
function of any organ acquired during life of an
individual (in response to changes in environment) are
inherited by offsprings & keep on adding the same over
period of time leading to origin of new species
ASSUMPTIONS
a) Internal vital force – All living organisms can increase
their size by virtue of presence of internal vital fore
b) Effect of environment & new needs- A change in
enironment brings about change in organism which
lead to production of new strutures and habits
c) Use and disuse of organ- The organs which are in use
developed better than the ones not in use.
d) Inheritane of acquired characters- Whatever an
individual acquires in his life time is itransmitted to
the next generation & this process continues for
generations leading to origin of new species.
1
2
3

4. Use & disuse of organs does
seem to influene the organis
to large extent
Only those variations transfe
to next generation whih are
related to germplasm
Environmrnt influences the
organism & changes its heri
Internal vital force dont
play any role in evolution01
02
03
04

5. ASSUMPTIONS
a) Prodigality in nature/ over production- all organisms have great
reproductive or fertility potential . Organisms produce no. Of
organisms than actually survive
b) Limited food and space
c) Struggle for existence- since organisms multiply in geometric ratio
and there is sacrcity of food and space there is struggle for existence.
Types of struggle
• Intraspecific struggle- struggle between individuals of same species.
• Interspecific struggle – struggle between individuals of different
species.
• Environmental struggle- struggle between organism & environment.
d) Variations & heridity- due to competion the organisms are ompelled
to hange themselves according to the ondotions around them hene
there are variations among the organisms which are passed from one
generation to other and hence after many years the accumulated
variations lead to formation of new species.
e) Natural selection & Survival of the fittest- such individuals have
more chances of reproduction than the organisms having less useful
variations . This differential reproduction inreases the no. of
individuals having useful variations i.e those organisms survive which
are fit and are naturaly selected by the environment.
Given by – CHARLES DARWIN

6. Presented by J. Huxley, H.J Miller, Gates, Weisman, E. Mayr,
Hugo de Veries
All organisms multiply in geometrical ratio & produce more
offsprings than can survive
There is limited food and space hence they struggle for existence which is of
3 types- intraspecific, interspecific and environmental
The causes of genetic variations were explained on the basis of-:
a) Mutations – these are discontinuos variations which develop due to permanent change
in genotype.
b) Genetic recombination- They are new combinations of genes which are usually caused
by crossing over.
c) Hybridization- It is crossing of organisms which are genetially diffrent in one or more
traits.
d) Genetic drift- it is addition or elimination of certain characters when some organisms in
the population migrate, immigrate or dies . Hence changes in the gene frequency is
called genetic drift or SEWALL WRIGHT EFFECT.
e) Natural selection- if diffrential reproduction continues for many generations then the
genes of individuals whih repproduce more will become predominant in gene pool
f) Isolation- it is seggregation of population by some barriers which prvent interbreeding .
This reprodutive isolation leads to formation of new species.
g) Origin of new species

7. Mutations appear suddenly & produce their
effects immediately
A single mutation can produce a new species.
Same type of mutattions can occur in
different organisms
Nature selects useful mutations and delete
lethal mutations
Evolution is not a continuous process, it is a
discontinuous one.
Given
by
Hugo
De
VERIES

8. Genetic
Variations
Heridity &
Mutations
Natural selection
Reproductive
isolation
Speciation
The are variations
caused in genes
due to mutations
or gene
recombination
Chnges in genes
are transfered
from one
organism to
other
On basis of
diffrential
reproduction
organisms with
more useful genes
are naturaly
selected.
Various barriers
isolate the species
from one another
that they couldnot
interbreed
The phenomenon
of development of
new species from
the existing ones is
called speciation