Polygyny is a type of mating system that involves pair bonds between one male and several females. While this may at first seem unfair to females, in a polygynous system every female can usually have a mate, while only the most desirable males will find a mate. In human societies, polygyny is actually the most common type of mating system. This is reinforced by genetic data—it suggests that the Y chromosome sequences vary little within human populations. Thus, relatively few men have contributed a larger fraction of their chromosome pool in every generation.