Sep 222012

Organic evolution is one of the most interesting and mysterious things that can be studied. By this, we can know about the evolution of living organisms on the earth. Though the answer of the question “How living beings came into existence?” is not found till today, many hypothesis and theories have been given to give the answer of this question. Among those theories, Lamarckism is also the one.

Lamarckism, which is also known as The Theory of Inheritance of Acquired Characters, was given by French Naturalist Jean Baptiste de Lamarck (1744 A.D.-1829 A.D.). He was the grandson of famous scientist Erasmus Lamarck. He stated this theory in the year 1809 through his famous book called “Philosophie Zoologue”. Some main facts of Lamarckism are given below:

  1. Tendency to grow in size: Some internal factors like internal needs of life tend to increase the size of the part of an organism upto the certain limit. The limit after growth is determined by life itself.
  2. Effect of use and disuse of organs: In the changing environment, all organs of the body are not used equally. The organs which are used regularly become more strong and more developed. On the other hand, some organs gradually become weak and degenerate due to continuous disuse of organs. Therefore, Lamarckism is also called as “theory of use and disuse of organs”.
  3. Inheritance of acquired characters: All the changes which an organism acquires during its lifetime are inherited. The acquired characters go on accumulating through generations and finally in long course of time, produce an organism which is entirely different from the pre-existing organisms. The acquired characters are appeared due to use and disuse of organs.
  4. Effect of environment: Changing environment affects the mode of life, body structure and habits. Variation in the environment of an organism creates a new need to change for adaptation, otherwise it will not be able to survive.

Drawbacks of Lamarckism

The drawbacks of Lamarckism are given below:

  • Lamarckism explained about the tendency to grow in size. There are many cases where evolution process takes place not only with the increase in size but also through a reduction in size.
  • Lamarckism also explained that new organs result from new needs of the organisms. This is quite false.

Weisman Theory (Germplasm Theory)
German scientist Weisman was the first person to object Lamarckism by doing an experiment. He did an experiment by cutting tails of white mice for more than twenty generations. But he found that the length of the tails of off-springs were normal, not shorter.

On the basis of this experiment, Weisman proposed his own theory which is known as Germplasm Theory. This theory shows that in an organism, two types of cells can be found which are somatic cells and germ cells. The acquired characters cannot be inherited, for such characters are in the somatic cells only whereas inherited characters are transferred in the germ cells only.