Question

Mention the two principles through which Lamarck explained his ideas.

Answer 1

1. Use and disuse: Parts of the body that are extensively used become larger and stronger, while those that are not used deteriorate. He explained this by taking the example of a giraffe. Lamarck suggested that the giraffe evolved from ground-feeding herbivores. But at a later stage, the area fell short of its ground-level vegetation, and thus, the giraffe took to feeding from trees. The constant stretching of its neck and forelimbs over many generations resulted in these structures becoming longer and stronger so as to reach higher foliage (leaves).
2. Inheritance of acquired characters: It stated that an organism could pass its modifications to its offspring. Lamarck postulated that the long, muscular neck and forelimbs of the living giraffe were passed on to them by their ancestors, and the same characters would continue to appear generation after generation.