A species with a number of more or less independent subpopulations is said to have population subdivision.

In nature, a species may consist of a number of separate populations, each more or less isolated from the others. The members of a species might, for example, inhabit a number of islands, with each island population being separated by the sea from the others; individuals might migrate between islands from time to time, but each island population would evolve to some extent independently.

An important consequence of population subdivision is the Wahlund effect: the frequency of homozygotes higher in populations which contain subdivisions than in fused populations.