Question

Explain industrial melanism.

Answer 1

Industrial melanism is a phenomenon where darker-colored variants of a species become more common due to environmental changes caused by industrial pollution. A classic example is the peppered moth (Biston betularia) in British woodlands. Before the Industrial Revolution, the light grey form of the moth was abundant because it could camouflage against the light-colored lichen-covered tree trunks. The dark-colored mutant was rare as it was conspicuous and preyed upon by birds.

However, the burning of coal during industrialization resulted in soot deposition on tree trunks, turning them black. This made the light-colored moths more visible and vulnerable to predation, while the dark-colored moths became better camouflaged. Consequently, the population of dark (melanic) moths increased dramatically, reaching about 90% in affected areas. Later, with pollution control measures and cleaner environments, the tree trunks lightened again, favoring the light-colored moths, whose population increased.

This shift in moth coloration due to changes in environmental pigmentation demonstrates natural selection, where environmental pressures select for the phenotype best suited for survival, leading to changes in allele frequencies in the population over time. Industrial melanism thus serves as a clear example of evolution by natural selection in response to environmental change.