While members of most sexually reproducing species are either male or female, individuals belonging to the rest of the biological world are not so simply defined. Hermaphroditic creatures reproduce both as a male and as a female, providing a fascinating example of alternative sexual practice and its ecological and evolutionary successes.Eloquently written by an award-winning biologist and pioneer in molecular ecology, this primer traces the phenomenon of hermaphroditism throughout Earth's species and the adaptive significance of alternative sexual systems. The volume's accessible and richly illustrated text covers the evolutionary origins of hermaphroditism and its historical and fictional instances, proving the relevance of dual sexuality to the everyday world. John C. Avise describes the genetics, ecology, phylogeny, and natural history of hermaphroditic plants, fish, and invertebrate animals and details organisms that either reproduce simultaneously as male and female or switch routinely between one sex and the other. Filled with surprising creatures and inherently compelling topics, this book stands alone in its clear yet comprehensive treatment of hermaphroditism and its unique challenge to the supremacy of separate sexes.