Question

Which type of selection is industrial melanism observed in moth, Biston betularia ?

• A. Stabilising
• B. Directional
• C. Disruptive
• D. Artificial

Hint:

The dark form increased in sooty areas, so the population shifted to one extreme.

Answer 1

The Correct Option is B

Step 1: Recall the example:
Before industrialisation, white-winged peppered moths were common because they hid well on lichen-covered trees.
After industrialisation, soot darkened the tree trunks. Dark-winged (melanic) moths hid better and white ones were eaten by birds.

Step 2: Identify the selection type:
The population changed in one direction: the frequency of the dark form increased and the white form fell.
Natural selection that shifts a trait towards one extreme is called directional selection.

Step 3: Check each option:
Stabilising selection favours the average and removes both extremes, so (A) is wrong.
Disruptive selection favours both extremes and removes the average, so (C) is wrong.
Artificial selection is done by humans on purpose, but here birds and the environment acted, so (D) is wrong.
Directional selection fits, so (B) is correct.

Final Answer:
Industrial melanism is directional selection, option (B).