A mystery emerged in Britain during the 1800s. An Industrial Revolution had just taken hold. Busy factories started to darken the skies with smoke from burning wood and coal. The sooty pollution blackened tree trunks. In short order, Victorian scientists took note of a change, too, among peppered moths (Biston betularia). A new, all-black form emerged. It came to be called B. betularia carbonaria, or the “charcoal” version. The older form became typica, or the typical form. Birds had been able to easily spot the old-style, lightly colored peppered moths as they settled onto soot-blackened tree trunks. Their new dark cousins instead blended in. The result: those carbonaria were less likely to be eaten.

Not surprisingly, numbers of light-colored moths started to fall as their dark cousins increased. By 1970, in some polluted regions nearly 99 percent of peppered moths were now black.

Source

What process caused changes in the frequency of traits within the peppered moth population?

A artificial selection

B sexual reproduction

C natural selection

D mutation