The evolution of hermaphroditism among animals.

Abstract

Possible selective advantages, including some new ones, for hermaphroditism are reviewed. It is proposed that hermaphroditism should evolve under the following conditions: (a) where it is hard to find a mate; (b) where one sex benefits from being larger or smaller than the other; or (c) where there are small, genetically isolated populations. Some conceptual problems and a comparative means of study are discussed. The literature is reviewed to show the conditions under which hermaphroditism may have evolved. It is concluded that all thee explanations have some validity.