Q.90 Increase in the existent population of grey peppered moth, Biston betularia, during industrial
revolution in Britain is an example of which ONE of the following evolutionary processes?
(A) Neutral selection (B) Disruptive selection
(C) Directional selection (D) Stabilizing selection

The increase in the grey (melanic) population of the peppered moth (Biston betularia) during Britain’s Industrial Revolution exemplifies directional selection. This classic case of industrial melanism demonstrates natural selection favoring one extreme phenotype due to environmental change.​

Question Analysis

The query from CSIR NET Life Sciences tests understanding of evolutionary processes, specifically how pollution shifted moth populations. Pre-Industrial Revolution, light-colored moths dominated as they camouflaged on lichen-covered trees, evading bird predation. Soot from factories darkened trees, killing lichens and making light moths conspicuous, while melanic (dark) mutants, arising around 1819, blended in better and increased to 95-98% by 1895.​

Option Explanations

• (A) Neutral selection: Refers to neutral theory of molecular evolution, where genetic changes neither benefit nor harm fitness and spread by genetic drift, not selection. This does not apply, as melanic form had a survival advantage via camouflage.​

• (B) Disruptive selection: Favors both phenotypic extremes over intermediates, creating a bimodal distribution and potentially leading to speciation. Here, only the dark extreme thrived; light and intermediates did not.​

• (C) Directional selection: Favors one phenotypic extreme, shifting population mean toward that trait in response to environmental pressure. Matches perfectly: dark moths selected as pollution favored melanism.​

• (D) Stabilizing selection: Favors intermediate phenotypes, reducing variation around the mean in stable environments. Opposite occurred; extremes shifted due to change.​

Correct Answer: (C) Directional selection.​

The peppered moth directional selection during Britain’s Industrial Revolution showcases rapid evolution in Biston betularia. Light moths once thrived on lichen trees, but soot pollution darkened bark, favoring dark melanic forms through natural selection.​

Historical Context

Before 1848, light “typica” moths dominated, camouflaged against predators. A melanic mutation (carbonaria) emerged, spreading as factories blackened environments, reaching 98% in polluted Manchester by 1895. Cleaner air post-1956 reversed this, confirming selection’s role.​

Why Directional Selection?

This process shifts trait distribution toward one extreme when environments change. Dark coloration provided camouflage advantage, increasing survival and reproduction. Unlike other selections, it explains the unidirectional rise in grey peppered moth population.​

Relevance to Exams

Ideal for CSIR NET Life Sciences on evolutionary biology. Highlights natural selection over drift or neutral changes. Key for understanding adaptation in changing habitats.​