Lamarckism (Theory of Inheritance of Acquired Characters)
This theory was proposed by French biologist, Jean Baptiste de Lamark in 1809. It was published in ‘Philosphie Zoologique’ in the year 1809. It is popularly known as “The Inheritance of Acquired Characters in Organisms’.
Definition: Lamarckism or theory of inheritance of acquired characters can be defined as “The changes in structure or function of any organ acquired during the life-time of an individual in response to changes in the surrounding environment are inherited by its offsprings and keep on adding up over a period of time”. These changes lead to the origin of new species.
Postulates of Lamarckism or Inheritance of Acquired Characters
Lamarckism is based on three factors or postulates:
1. New Needs: Changes in the environment create new needs in living organisms so that these are better adapted or more suited to the changed environment. The organisms have to put in special efforts for the fulfillment of the new needs. These efforts lead to a change in the habits or behavior. The new need results in the formulation of new organ or a part in the body. If the need continues that organ or part continues to grow.
2. Acquisition of New Characters: New Characters are acquired by the living beings in two ways:
(a) By use and disuse: The new habits involve greater use of certain organs to meet the new need, and disuse or lesser use of certain other organs in changed conditions. The continuous use of an organ or organs keeps them functional and makes them stronger, larger and more efficient. Continuous disuse of an organ or organs leads to gradual reduction in their size and to their final disappearance.
Vestigial organs are examples of such non-functional organs in the modern forms. These were in the functional form in the ancestors. Thus by differential use and disuse of various body parts, an organism would change to some extent and acquire some characters and modify some other.
The changes acquired or accumulated in an organism during its life time by the use and disuse of organs or by the influence of the environment are called acquired characters.
(b) Effect of environment: Changes in temperature, light, medium, food, etc., influence the functioning and behavior of living beings and introduce changes in their structure. Thus organisms acquire certain new characters due to direct or indirect influence of environment.
3. Inheritance of Acquired Characters: The characters acquired by an organism during its life time are inherited to the next generation. In every generation some new characters were acquired or the older ones keep on increasing or improving. As a result, after a number of generations, the species gets modified into a new one.