The Effects of Natural Selection
As a result of natural selection, populations become better adapted to their environment; but the effects of natural selection are not always the same.

Peppered Moths—Changing With the Times

The difference between the two populations is obvious. How can this difference be explained by natural selection?

The offspring of dark moths are usually dark. If natural selection caused the change in the peppered moth populations, the dark moths must have been better adapted to their environment than the pale moths were. In what way?

Several species of birds eat peppered moths. During the day, the moths rest on lichen-covered tree trunks.

Air pollution in this area has killed most of the lichens and blackened the trees. Which color moths are better adapted to this environment, and are more likely to survive and leave offspring?

Natural Selection in Action
Experiments have confirmed that birds find and eat more dark moths on pale, lichen-covered trunks, but they eat more pale moths on blackened trunks.

So in an industrial area dark moths are more likely to survive and leave offspring, and over a period of time this would cause the proportion of dark moths in the population to increase. This would be enough to explain the rapid change in the peppered moth species around industrial towns last century.

Peppered moths show how natural selection can change the characteristics of a population.