It is most common in animals who associate in relatively small social groups, sich as chimpanzees and wolves. In both cases, as the young mature sexually, one sex, and only one (males in chimps) is driven out of the group and so forced to find sexual partners in other groups than their own.
In animals in large social groups, like wildebeest for example, it isn't necessary as the likelihood of sexual encounters with one's own kin is far less.