• In pre-industrial times, the light-coloured moths were well-camouflaged on lichen-covered tree trunks, so predators (birds) could not easily spot them.

• During the Industrial Revolution, soot and smoke darkened tree trunks, making light-coloured moths more visible and thus more preyed upon.

• A mutation in a single gene gave rise to the dark-coloured (melanic, Carbonaria) variety, which now had a selective advantage because they were better camouflaged in the new polluted environment.

• This is a classic example of industrial melanism and natural selection.