The increase of the dark form of the peppered moth in industrial England is a direct example of

Explanation

Soot darkened the tree trunks, so pale moths became conspicuous to birds while the dark variant was camouflaged, and the frequency of the dark form rose within a few decades. The variation already existed as a mutation and the environment merely decided which form survived to breed. It is not artificial selection because no human chose the breeders, and the moths did not darken through exposure to soot.