Natural selection can be compared with the process of passing a gravel-mix through a sorting machine, and getting separate piles of gravel, each with its own pebble size. In this analogy, which part of natural selection is represented best by the gravel mix? a. Over-reproduction b. Struggle for existence c. Variation d. The environment

The correct answer is option c, that is, variation.

Explanation:

In the given case, the gravel mix is to be selected on the basis of the size of pebbles, which is analogous to the organism selected in nature. In the given question, the sorting machine is analogous to the environment, that is, a selective force.

Like a specific environment permits the organisms exhibiting specific traits. For example, in a desert where the environment is hot and dry, only the species exhibiting the tendency to conserve water can thrive, similarly sorting machine will permit to distinguish gravel on the basis of the pebble size. Thus, different size of pebble resembles variation.