In biology, a hermaphrodite () is an organism that has complete or partial reproductive organs and produces gametes normally associated with both male and female sexes.[1] Many taxonomic groups of animals (mostly invertebrates) do not have separate sexes.[2] In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the "female" or "male." For example, the great majority of tunicates, pulmonate snails, opisthobranch snails, earthworms, and slugs are hermaphrodites. Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates. Most plants are also hermaphrodites.

Historically, the term hermaphrodite has also been used to describe ambiguous genitalia and gonadal mosaicism in individuals of gonochoristic species, especially human beings. The word intersex has come into usage for humans, since the word hermaphrodite is considered to be misleading and stigmatizing,[3][4] as well as "scientifically specious and clinically problematic."[5]

A rough estimate of the number of hermaphroditic animal species is 65,000.[6] The percentage of animal species that are hermaphroditic is about 5%. (Although the current estimated total number of animal species is about 7.7 million, the study [6], which estimated the number, 65,000, used an estimated total number of animal species, 1,211,577 from "Classification phylogntique du vivant (Vol. 2)" - Lecointre and Le Guyader (2001)). 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 processes are operating to direct the evolution of selfing in animals and plants.[6]

The term derives from the Latin: hermaphroditus, from Ancient Greek: , romanized:hermaphroditos,[7] which derives from Hermaphroditus (), the son 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;[8] according to the earlier Diodorus Siculus, he was born with a physical body combining male and female sexes.[9] The word hermaphrodite entered the English lexicon as early as the late fourteenth century.[10] Alexander ab Alexandro stated, using the term hermaphrodite, that the people who bore the sexes of both man and woman were regarded by the Athenians and the Romans as monsters, and thrown into the sea at Athens and into the Tiber at Rome.[11]

Sequential hermaphrodites (dichogamy) occur in species in which the individual is born as one sex, but can later change into the opposite sex.[12] This contrasts simultaneous hermaphrodites, in which an individual may possess fully functional male and female genitalia. Sequential hermaphroditism is common in fish (particularly teleost fish) and many gastropods (such as the common slipper shell), and some flowering plants. Sequential hermaphrodites can only change sex once.[13] Sequential hermaphroditism can best be understood in terms of behavioral ecology and evolutionary life history theory, as described in the size-advantage mode[14] first proposed by Michael T. Ghiselin[15] 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:

Dichogamy can have both conservation-related implications for humans, as mentioned above, as well as economic implications. For instance, groupers are favoured fish for eating in many Asian countries and are often aquacultured. Since the adults take several years to change from female to male, the broodstock are extremely valuable individuals.

A simultaneous (or synchronous) hermaphrodite (or homogamous) is an adult organism that has both male and female sexual organs at the same time.[12] Self-fertilization often occurs.

When spotted hyenas were first discovered by explorers, they were thought to be hermaphrodites. Early observations of spotted hyenas in the wild led researchers to believe that all spotted hyenas, male and female, were born with what appeared to be a penis. The apparent penis in female spotted hyenas is in fact an enlarged clitoris, which contains an external birth canal.[21][22] It can be difficult to determine the sex of wild spotted hyenas until sexual maturity, when they may become pregnant. When a female spotted hyena gives birth, they pass the cub through the cervix internally, but then pass it out through the elongated clitoris.[23]

Hermaphrodite is used in older literature to describe any person whose physical characteristics do not neatly fit male or female classifications, but some people advocate to replace the term with intersex.[26][27] Intersex describes a wide variety of combinations of what are considered male and female biology. Intersex biology may include, for example, ambiguous-looking external genitalia, karyotypes that include mixed XX and XY chromosome pairs (46XX/46XY, 46XX/47XXY or 45X/XY mosaic).

Clinically, medicine currently describes intersex people as having disorders of sex development, a term vigorously contested.[28][29] This is particularly because of a relationship between medical terminology and medical intervention.[30] Intersex civil society organizations, and many human rights institutions,[31][32] have criticized medical interventions designed to make intersex bodies more typically male or female.

Some people who are intersex, such as some of those with androgen insensitivity syndrome, outwardly appear completely female or male, frequently without realizing they are intersex. Other kinds of intersex conditions are identified immediately at birth because those with the condition have a sexual organ larger than a clitoris and smaller than a penis.

Some humans were historically termed true hermaphrodites if their gonadal tissue contained both testicular and ovarian tissue, or pseudohermaphrodites if their external appearance (phenotype) differed from sex expected from internal gonads. This language has fallen out of favor due to misconceptions and pejorative connotations associated with the terms,[33] and also a shift to nomenclature based on genetics.

Intersex is in some caused by unusual sex hormones; the unusual hormones may be caused by an atypical set of sex chromosomes. One possible pathophysiologic explanation of intersex in humans is a parthenogenetic division of a haploid ovum into two haploid ova. Upon fertilization of the two ova by two sperm cells (one carrying an X chromosome and the other carrying a Y chromosome), the two fertilized ova are then fused together resulting in a person having dual genitalial, gonadal (ovotestes) and genetic sex. Another common cause of being intersex is the crossing over of the SRY from the Y chromosome to the X chromosome during meiosis. The SRY is then activated in only certain areas, causing development of testes in some areas by beginning a series of events starting with the upregulation of SOX9, and in other areas not being active (causing the growth of ovarian tissues). Thus, testicular and ovarian tissues will both be present in the same individual.[34]

Fetuses before sexual differentiation are sometimes described as female by doctors explaining the process.[35] This is technically not true. Before this stage, humans are simply undifferentiated and possess a Mllerian duct, a Wolffian duct, and a genital tubercle.

Hermaphrodite is used in botany to describe a flower that has both staminate (male, pollen-producing) and carpellate (female, ovule-producing) parts. This condition is seen in many common garden plants. A closer analogy to hermaphroditism in botany is the presence of separate male and female flowers on the same individualsuch plants are called monoecious. Monoecy is especially common in conifers, but occurs in only about 7% of angiosperm species.[36] The condition also occurs in some algae.[37]

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