A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. Plant species in which individuals are either male or female are dioecious. The individuals of many taxonomic groups of animals, primarily invertebrates, are hermaphrodites, capable of producing viable gametes of both sexes. In the great majority of tunicates, mollusks, and earthworms, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the female or male. Hermaphroditism is also found in some fish species, but is rare in other vertebrate groups. Among plants the vast majority of angiosperms (flowering plants) are hermaphrodites. Most hermaphroditic species exhibit some degree of self-fertilization. The distribution of self-fertilization rates among animals is similar to that of plants, suggesting that similar pressures are operating to direct the evolution of selfing in animals and plants. A rough estimate of the number of hermaphroditic animal species is 65,000, about 5% of all animal species, or 33% excluding insects. Insects are almost exclusively gonochoric. There are no known hermaphroditic species among mammals or birds. About 94% of flowering plant species are either homoecious (all flowers produce both male and female gametes) or monoecious, where both male and female flowers occur on the same plant. There are also mixed breeding systems, in both plants and animals, where hermaphrodite individuals coexist with males (called androdioecy) or with females (called gynodioecy), or all three exist in the same species (called trioecy). Sometimes, both male and hermaphrodite flowers occur on the same plant (andromonoecy) or both female and hermaphrodite flowers occur on the same plant (gynomonoecy). Hermaphrodism is not to be confused with ovotesticular syndrome in mammals, which is a separate and unrelated phenomenon. While people with the condition were previously called "true hermaphrodites" in medical literature, this usage is now considered to be outdated as of 2006 and misleading, as people with ovotesticular syndrome do not have functional sets of both male and female organs.
Etymology The term hermaphrodite derives from the Latin: hermaphroditus, from Ancient Greek: ἑρμαφρόδιτος, romanized: hermaphroditos, which derives from Hermaphroditus (Ἑρμαφρόδιτος), the child of Hermes and Aphrodite in Greek mythology. According to Ovid, he fused with the nymph Salmacis resulting in one individual possessing physical traits of male and female sexes. According to the earlier Diodorus Siculus, he was born with a physical body combining male and female sexes. The word hermaphrodite entered the English lexicon as early as the late fourteenth century.
Animals
Sequential hermaphrodites
Sequential hermaphrodites (dichogamy) occur in species in which the individual first develops as one sex, but can later change into the opposite sex. (Definitions differ on whether sequential hermaphroditism encompasses serial hermaphroditism; for authors who exclude serial hermaphroditism, a sequential hermaphrodite is also stipulated to only change sex once.) This contrasts with simultaneous hermaphrodites, in which an individual possesses fully functional male and female gametes. Sequential hermaphroditism is common in fish (particularly teleost fish) and many gastropods (such as the common slipper shell). Sequential hermaphroditism can best be understood in terms of behavioral ecology and evolutionary life history theory, as described in the size-advantage mode first proposed by Michael T. Ghiselin which states that if an individual of a certain sex could significantly increase its reproductive success after reaching a certain size, it would be to their advantage to switch to that sex. Sequential hermaphrodites can be divided into three broad categories:
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