Question

Taking industrial melanism as an example, explain the process of natural selection.

Answer 1

Industrial melanism in the peppered moth (Biston betularia) is a classic example of natural selection. Before the industrial revolution, the light grey form of the moth was abundant since it could easily camouflage on the lichen-covered, light-colored tree trunks, making it less visible to predators like birds. The dark-colored (melanic) form was rare because it was more conspicuous and thus more likely to be eaten.

However, with industrialization and the burning of coal, soot deposited on tree trunks turned them dark. This environmental change made the light-colored moth highly visible to predators, leading to its decline. Conversely, the dark-colored moth now had better camouflage, reducing its chances of predation. Consequently, the frequency of the melanic form increased dramatically, becoming the dominant form in polluted areas.

Later, with pollution control and cleaner environments, tree trunks became lighter again, and the light-colored moth populations increased once more.

This phenomenon demonstrates natural selection acting on variation: environmental changes altered the selective pressures, favoring the survival and reproduction of the moth variant best suited to the new conditions, thereby shifting population frequencies over time in response to natural selection.