Theory Examples Concept of Lamarck regarding the Evolution

 

Jean Baptiste de Lamarck Was a French naturalist and gave the theory of Inheritance of acquired character with reference to evolution.

This illustration of Lamarck was quite different from Theory of Darwin. It was published in 1809 in his book philosophie zoologique.

According to this theory the characteristics  that are acquired by an organism during their lifetime in response to environmental conditions are passed to their offspring.The theory of Lamarck can be understood by the following basic features -

Organisms and their organs have a natural tendency to continuously increase in size from generation to generation.

Continuous changes in Environmental conditions directly influence the way of living and nature of organisms. These environmental conditions affect their structure organization.  

The body parts that are more usable that they  are more developed  and the  parts that are less usable than their development is  decreased. 

The parts of the body that are poorly developed or that are more developed are passed  from generation to generation as a hereditary character.

Lamarck emphasized only lesser or more use of the body part  therefore it is also often referred to as the theory of use and disuse of organs.

Lamarck gave several examples regarding lesser or more use of the body part. Out of these example, the two are most popular that are given below-

Example no 1  - The present species of Giraffe lives in the arid African desert which has no vegetation except for a few trees in a widely scattered area. The neck and fore limb of these giraffes are quite elongated which makes them able to reach the leaves of high trees.

He also claimed  that the ancestor from which present species of Giraffe has evolved were ordinary deer and fed vegetation  like them because at this time, this area was rich in vegetation. As the climate of this area started changing it gradually turned into desert and its rich vegetation gradually disappeared.

Only a few trees that grew also gain height generation after generation. Giraffes in each generation therefore had to stretch their neck and forelimb  to reach to the leaves of these trees. Due to this continuous effort of Giraffe, their  neck and forelimb  gradually became longer and gave rise to modern species. This example was  given by Lamack to illustrate the effect of a better use of organs. 

Example no 2 - The example of the snake was given by Lamarck also to illustrate the effect of disuse  of organs. He stated that the ancestors of the modern snake were like  limbed lizards which were forced to live in a thick forest. As an adaptation to forest life, the body gradually elongated and adopted creeping for the fast  locomotion and lost the utility of leg therefore gradually legs were disappeared.