Lamarcksim(Theory of inherent of acquired character)
French naturalist J.B Lamarck proposed the theory of evolution in 1809 entitled Inheritance of acquired character through his “philosophic zoology book”. It is also known as Lamarckism.
Lamarckism states that “An organism acquires new modification for adaptation in its environment in the course of times which are transferred to its offspring automatically and become a part of heredity.”
Lamarckism can be summarized in the following points-
- Tendency to grow– Each and every organism has the natural tendency to grow . New structure appears because of inner want of organism. The body part of organism grows up to a limit that is determined by the life itself.
- Environment effect and formation of new organ– Gradual change in the environment factor like variation in temperature, light, food etc. change the animal needs. To fulfill these new needs the living organisms have to change their habit or behavior. The change in habits results in the modification of the organs and new organs are created.
- Use and disuse of organ– use and disuse of organs affect their form, structure and mode of function .Continuous use of organs keep them active and make them larger stronger and more efficient. The continuous disuse makes them weaker and undeveloped. Later they disappear.
- Inheritance of acquired character– the character acquired by and individual by use and disuse of organs and by environment effect are transmitted by hereditary to the next generation. In every generation fresh character are acquired after a no of generation and species are modified into new ones.
To support his views the forwarded following example.
-Giraffes- The ancestors of giraffes were small deer like animals. Due to shortage of grasses they started feeding leaves of long trees. To reach the leaves they started to extend their neck and limbs . During the course of time, this was transmitted to the next generation; in which further elongation occur due to similar effort. This resulted in present day giraffes.
– Snakes- The absence of feet in snakes is an example of disuse . The snakes were generally 4 limbed animals. But they adopted creeping habits and lived in burrows. Due to this they lost limbs resulting in present day snakes.
Criticism of Lamarckism-
- According to Lamarck, the eyes are developed more in the course of time but it gets weaker during course of time.
- The son of boxer and wrestler doesn’t become a fighter from birth.
- Boring of ear and nose has been practiced by Indian women since ages but the characters aren’t inherited to the offspring.
- weishman ,cut the tail of mice continuously for 20 generation but no tail less variety were obtained.
- He couldn’t explain the vitality of structure in intial stage of development.
Several experiments were conducted by a number of scientists to modify Lamarckism, to make it more modify Lamarckism, to make it more reliable and acceptable; it is called “Neo-Lamarckism”.The major contribution to correct the Lamarck theory was made by “A.Weishman”. On the basis of his experiment on mice, he proposed “Germ plasm theory”.
Ac/to this theory,” There are two types of cells in the organisms i.e somatic cells and germinal (reproductive) cells, the changes in somatic cells aren’t inherited whereas the changes in germinal cells are only inherited