Lamarckism: Inheritance of Acquired Characters (Use and Disuse)

Lamarckism has two parts. First, use and disuse of organs: an organ used a lot grows bigger and stronger (like a blacksmith's arm), while an organ not used becomes weak and shrinks. Second, inheritance of acquired characters: the change gained during the parent's life is passed to the offspring. For NEET, remember both ideas travel together in Lamarck's theory.

Lamarck said early giraffes had short necks. To feed on leaves high up on tall trees, they kept stretching their necks. This stretching (use) made the neck longer during their life. Lamarck said this acquired long neck was passed to the next generation, so over many generations giraffes got long necks. NCERT gives this exact example, then says nobody believes it now.

Rejected. NCERT clearly states about Lamarck's giraffe idea: "Nobody believes this conjecture any more." Body changes made during life (acquired characters) do not reach the reproductive cells (gametes), so they are not passed to offspring. Only changes in genes are inherited. NEET often tests that Lamarckism is a discarded theory.

Characters gained during life, like bigger muscles from exercise or a scar, affect only body (somatic) cells, not the sex cells (gametes) that form the next generation. Since the DNA in gametes is not changed by such body changes, the offspring do not inherit them. This is why cutting a mouse's tail for many generations still gives mice with tails.

Both used the giraffe, but differently. Lamarck said each giraffe stretched its neck and passed the longer neck to its young (inheritance of acquired characters). Darwin said giraffes already had natural variation in neck length; those with longer necks got more food and survived and reproduced (natural selection). NEET loves this contrast, so keep the next page darwin-vs-lamarck ready.

Jean Baptiste Lamarck, a French biologist, proposed it. It is also called the theory of inheritance of acquired characters or the use and disuse theory.

It means the changes an organism gains during its own lifetime (acquired characters) are passed on to its children (inherited). Lamarck believed this; modern biology rejects it.

The blacksmith example: a blacksmith develops strong arm muscles by using them (use), and Lamarck claimed this strength would pass to his children. Also, the loss of eyes in cave animals due to disuse. These are Lamarckian ideas, now rejected.

Yes. NEET can ask who proposed the theory, the two key ideas (use and disuse, inheritance of acquired characters), the giraffe example, and the fact that it is now rejected. It is also compared with Darwinism.

Darwin's theory of natural selection is the accepted explanation. Instead of stretching and inheriting, natural selection acts on pre-existing inherited variation, favouring individuals that survive and reproduce better.