In the context of the organic evolution, the loss of limbs of snakes is explained by the phenomenon of

1. The question asks how the theory of organic evolution explains the loss of limbs in snakes. 2. Lamarck's theory of evolution (now largely discredited in its original form but historically significant) included the principle of 'use and disuse of organs' (Option A). 3. This principle suggested that organs that were frequently used would develop, while those that were not used would gradually degenerate and disappear over generations. 4. In this context, it was proposed that ancestral snakes stopped using their limbs (perhaps due to adaptation to living in burrows - Option B, which is a related but distinct concept explaining *why* disuse might occur), leading to their gradual reduction and eventual loss. 5. Lamarck also proposed the 'inheritance of acquired characters' (Option D), suggesting these changes due to use/disuse could be passed on. While modern evolutionary synthesis emphasizes natural selection (Option C) acting on random mutations, the specific explanation historically linked to the gradual loss of limbs due to lack of necessity is the Lamarckian concept of 'use and disuse'.