Lamarck Theory of Evolution

Lamarckism 

Lamarck was the great biologist and taxonomist. He was the first scientist to put forward the theory of organic evolution, this theory was published in a book philosophic zoolgique. His theory is also called inheritance of acquired characters.

The assumptions made by Lamark are listed below:

1.   Direct effect of environment:

According to Lamarck, environment has direct effect on the habit and Habitat of living organisms. The change in the environment leads to the origin of new needs in the living organisms to fulfil the new needs they had to change their habits or behaviour .

2.   Use and disuse of organs:

To fulfil the new needs some of the organisms use some of its organs very much and some organs very less the organs which were used very much developed very much and the organs which are used less disappear or become vestigial. So, the organisms acquire certain new characters during its life time called acquired characters.

3.   Inheritance of acquired characters:

Lamarck believed that acquired characters passes generation after generation and after many generation , these characters accumulated to form new species .

Evidences in support of Lamarkism :

                                The modern long necked giraffe had evolved from short necked ancestors. Their ancestors lived in the forest and grazed on the grasses .Due to the change in the environment, the ground became barren which forced the Giraffe to feed on leaves of large trees. TO get the leaves they started to use their neck and forelimbs very much, in due period these organs became taller and modern giraffe was evolved.

                In the snake, due to the disuse of limbs and girdles, these organs disappeared.

Criticism of Lamarckism

1.   Strong muscles of wrestler is not found in their offspring.

2.   Weishmann was a German biologist he pot forward a theory continuity of germ plasma. According to this theory, two types of cells found in the body i.e. somatic and germinal cells .Somatic cells determine particular organ which germinal cells determine hereditary characters. It was concluded that use and disuse of organs and change in the environment effect only somatic cell, acquired characters must be lost with the death of organism and they have no roll in evolution. He cut the tail of mice for many generation, he found that there was equally long tail in the last generation as in the first.