Within a population of fish, exists in the form of body color. some fish are orange and some fish are red.

In populations of all living things, there is a variation of different traits. This is important for the process of evolution and natural selection because if the individuals in the population vary in size, shape, color or any other morphological or physiological trait, the individuals can be more or less successful because of them and therefore natural selection can filter the variations that are the fittest for that environment.