LAMA RCKISM OR LAMARCK’S THEORY OF EVOLUTION
- B. Lamarck proposed theory according to this hypothesis.
- The continuous use of any of the organ would develop that organ while disuse would result in
gradual weakening and its ultimate the reduction and disappearance in the subsequent of
- Lamarck proposed the example of the long neck and fore limb of giraffe.
- He proposed that the ancestors of giraffe were small necked and gazed on grasses.
- The grass was destroyed or become unavailable so they had to stretch their necks to reach
the leaves which were higher off the ground.
- Thus as a result of continuous stretching of the neck for generations, the present giraffe with
longer neck and longer fore-limbs were evolved.
- To explain disuse of organs he took an example of modern snakes.
- He said like other reptiles, ancestors of snakes had four limbs to move on land.
- However to escape from their enemies, they had to hide under stones or in holes by creeping
in narrow cracks in rocks.
- This kind of movement requires muscles rather than limbs.
- Therefore as a results of disuse of limbs generation after gen9ion1 the snakes lost thcir
limbs and their bodies become cylindrical and elongated.
What is Darwinlcm, Describe its main features?
DARWINISM OR DARWIN’S THEORY OF EVOLUTION
- Charles Darwin (1809-1802) was an English man; he studied different plants and animals,
collected new specimens and categorized them.
- In the year 1859, he published a book “Origen of species by means of Natural selection” in
which he presented simple evidences in favour of evolution and proposed the mechanism of
origin of species.
MAIN FEATURES OF DARWINISM
The main points of the Darwin’s theory are as follows:
I). OVER PRODUCTION
- Living organisms reproduce rapidly so that the number of offspring could increase
- II) STRUGGLE OF EXISTENCE
- Due to the limited available resources of food, shelter, etc the offspring of species complete
not only with each other but also with the members of different species to share these
resources. In this struggle a large number of individuals of each species are eliminated. As a
result the population remains stable.
III) HERITA5LE VARIATIONS
- Darwin concluded that survival in struggle for existence is not random but depends upon in
part on the heredity constitution of the, surviving individuals. Those individuals whose
inherited characteristics fit them best to their environment would su9ive and produce more
offspring than less fit individuals who will vanish.
Iv) NATURAL SELECTION
- Nature selects the fittest individuals to survive and reproduce. favorable variations are
preserved through their inheritance to new young ones.