The theory of evolution

                    THE THEORIES OF EVOLUTION

                                                                                                                                                                 

HUMAN EVOLUTION

→LAMARCKISM OR LAMARCKS THEORY OF INHERENTENCE OF AQUIRED CHARACTERS.

→DARWINISM OR DARWIN'S THEORY OF NATURAL SELECTION.

→MODERN CONCEPTS OF EVOLUTION / SYNTHETIC OF EVOLITION.

LAMARCKISM

LAMARCKISM  is the first theory of evolution ,which was proposed by jean baptiste de lamarck a french biologist.

Although the outline of the theory was brought to notice in 1811, but his famous book "philosopic zoologique" was published in 1809, in which he discussed his theory in details.

lamarcks propotion

Internal vital force;all the living things and their component parts continually increase due to vital force.

Effect of  environments and new needs :  environment influence all type of organism . A change in environment brings about changes in organism. it gives rise to new needs.

New needs or desire  :  produce new structure and change habits of the organism. doctrine of desire is called appetency

Use and disues of organs : if an organ is constantly used it would be better developed where as disuse of organs result in degeneration.

Inheritance of acquired character : whatever character  an individual acquires in its life time due to internal vital force effects of environments , new needs and disuse of organs they are transmitted into the next generation.

After several generation, the variation are accumulated up to such extent that they give rise to new species.

long neck girraf     

Ancestors of giraff had a small neck and small forelimb.

They were living in places with .ittle vegetation so they had to stretch their neck and forelimbs to take leaves for food, which results in the slight elogination of these part.

whatever they acquired from one generation to another is transmitted to next generation.

 Aquatic birds like ducks has evolved from the terrestrial ancestor.

Snacks have evolved from lizards like ancestor which had two pairs of limbs

The ancestor of these birds were capable of flying, but due to some environment factors they had plenty of food and well protected.

so they did not use their wings  and that why they later become vestigial.

Ancestors of deer were not having much speed of running, but as they needed protection from other animals of that time they started running, due to which present speed was achieved by the deer.