Explain the principles of Lamarckian theory.

Explanation

(a) Lamarckism is the hypothesis that an orgganism can pass on characteristics, that it has acquired through use or disuse, during it.s lifetime to the offspring. Lamarck.s theory of evolution was published in .Philosophic Zoologique. in the year 1809.
Lamarckism is popularly known as .Theory of inheritance of Acquired Characters.. or ..Use and Disuse theory..
(b) (i) Internal vital force :
Due to the inherent ability of the living organisms or their component parts tend to increase in size continuosly.
(ii) Environment and new needs :
A change in the environment brings about changes in the need of the organisms. In response to the changing environment, the organisms develop cartain adaptive characters. The adaptations may be in the form of develoopment of new parts of body.
(ii) Use and disuse theory :
Lamarck.s use and disuse theory states that, if an organ is used constantly the organ develops well and gets strengthendes. When an organ is not used for a long time, it gradually degenerates The ancestors of Giraffe were provided with short neck and short forelimbs. Due to shortage of grass, they are forced to feed on leaves from trees. The continuous strtching of their neck and forelimbs, resulted in the development of long neck and long forelimbs, which is an example for constant use of an organ. The degenerated wing Kiwi is an example for organ of tisuse.
(iv). Theory of Inheritance of acquired characters :
Animals respond to the changes, When is a change When there is a change in the environment. The develop adaptive structures. The characters, developed during their life, in response to the environment changes are called acquired characters. The acquired characters are transmitted to the offspring by the process of inhertance.