Move over, moths! There’s a new kid in town!
During the Industrial Revolution, naturalists in England noticed that the incidence of normal, light-colored peppered moths (Biston betulari) had become scarce in the vicinity of various urban centers. Instead, they were finding a melanistic (dark colored) variety. At the same, time, pollution had caused the local trees to get darker. In 1896, J.W. Tutt proposed that this change was an example of natural selection. The light moths lost their camouflage effect when they sat on the new dark trees, so they got eaten by the local birds. Hence, the moths with the gene for melanism fared better and became prevalent.
The issue was hotly debated and thoroughly investigated through the first half of the twentieth century, and has since become one of the best known and best supported examples of natural selection. You probably remember it from your high school biology class.