Question

Enumerate Lamarck's propositions about evolution. Describe the examples given by Lamarck in support of the theory of use and disuse.

Answer 1

Introduction: Lamarck proposed that environmental change leads organisms to acquire changes that may be passed to their offspring.

Propositions

1. Organisms or their organs tend to increase in size or complexity.
2. A new need or changed environment may lead to the development of new organs.
3. Frequent use strengthens or enlarges an organ, while disuse weakens or reduces it.
4. Acquired characteristics are inherited by offspring.

Examples of use and disuse: Lamarck explained that giraffes repeatedly stretched to reach high leaves, developing longer necks and forelegs that were inherited. He also attributed webbed feet in ducks and frogs to swimming, long legs in herons to stretching in water, and the elongated, legless form of snakes to ancestors stretching their bodies while crawling through vegetation.

Lamarck’s account made use and disuse central to evolution, but inheritance of acquired characteristics is not supported by evidence such as Weismann’s mouse experiment.