Question

Which statement is correct regarding Biston betularia, a species of moth found in England during the late 19th century?

Options

• The black colouration of moth was caused by pollution from burning coal.

• Black moths were covered with soot from coal burning factories.

• These moths were killed by devastating fungus Phytophthora.

• An occasional mutation caused black moth to be borne.

Answer 1

An occasional mutation caused black moth to be borne.

Explanation:

The black coloration of the moth Biston betularia (melanic form) is due to an occasional mutation that produced dark-colored individuals. This mutation was initially rare. Before the industrial revolution, the grey form was predominant as it was camouflaged against lichen-covered tree bark. However, the environmental change caused by industrial soot darkening the trees made the black morph less visible to predators, giving it a selective advantage. The mutation itself caused the black coloration, but the industrial smoke changed the selective pressures, favoring the black moths.