The mice live in dark, rocky terrain. If they are spotted, owls will eat them.
More mice have been born than can survive. There aren't enough resources or space for all of them to survive. Some of the mice are seen and eaten by the owls.
Some mice are white, while some are black. But all mice are fighting to survive and not get eaten by the owls.
The black-colored mice blend in with the darker rocks. Because the white-colored mice are easier to see, the owls eat more white-colored mice than black-colored mice.
The black-colored mice are more adapted to their environment, and so they are better at hiding from the wolves. As a result, the black-colored mice are eaten less and survive longer.
The black-colored mice live longer, so they can reproduce more. Then, the black-colored mice give their color trait to their offspring. Over time, the population in the area has more black-colored mice than white-colored mice