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reproductive biology Reproductive biology includes both sexual and asexual reproduction. Reproductive biology includes a wide number of fields: * Reproductive systems * Endocrinology * Sexual development (Puberty) * Sexual maturity * Reproduction * Fertility Huma ...
, a hermaphrodite () is an
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
that has both kinds of reproductive organs and can produce both
gametes A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
associated with male and female sexes. Many taxonomic groups of
animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...
s (mostly invertebrates) do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of
sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
in which either partner can act as the female or male. For example, the great majority of
tunicates A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time cal ...
,
pulmonate Pulmonata or pulmonates, is an informal group (previously an order, and before that a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includ ...
molluscs, opisthobranch,
earthworms An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. ...
, and
slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a smal ...
s are hermaphrodites. Hermaphroditism is also found in some
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of liv ...
species and to a lesser degree in other
vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
. Most
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae ex ...
s are also hermaphrodites. Animal species having different sexes, male and female, are called gonochoric, which is the opposite of hermaphrodite. There are also species where hermaphrodites exist alongside males (called androdioecy) or alongside females (called gynodioecy), or all three exist in the same species (called
trioecy Trioecy, or subdioecy, is a rare sexual system characterized by the coexistence of males, females, and hermaphrodites. It has been found in both plants and animals. Trioecy is sometimes referred to as a mixed mating system alongside androdioecy an ...
); these three systems are sometimes called mixed breeding systems. In plants there are cases where male flowers and hermaphrodite flowers occur on the same plant (
andromonoecy Andromonoecy is a breeding system of plant species in which male and hermaphrodite flowers are on the same plant. It is a monomorphic sexual system alongside monoecy, gynomonoecy and trimonoecy. Andromonoecy is frequent among genera with zygomorph ...
) or female flowers and hermaphrodite flowers on the same plant (
gynomonoecy Gynomonoecy is defined as the presence of both female and hermaphrodite flowers on the same individual of a plant species. It is prevalent in Asteraceae but is poorly understood. It is a monomorphic sexual system alongside monoecy, andromonoecy a ...
). The term hermaphrodite is commonly used for abnormal cases of
dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...
animal species but according to geneticist Michael Majerus this definition should be distinguished from the scientific definition. In recent years the term hermaphrodite applied to humans has fallen out of favor since there have been no identified cases of a human reproducing as both male and female, with some biologists saying hermaphroditism does not occur in humans. Intersex activists have preferred the word '' intersex'', since the word ''hermaphrodite'' is considered to be stigmatizing, as well as "scientifically specious and clinically problematic." There are no hermaphroditic species among
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...
s or birds. According to David B. Rivers there is controversy around hermaphroditism in
insect Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, Thorax (ins ...
s with some experts believing it does not occur. Hermaphroditism is said to occur in one or two insect species. A rough estimate of the number of hermaphroditic animal species is 65,000. The percentage of animal species that are hermaphroditic is about 5% in all animal species, or 33% excluding insects. (Although the current estimated total number of animal species is about 7.7 million, the study, which estimated the number, 65,000, used an estimated total number of animal species, 1,211,577 from "Classification phylogénétique 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 pressures are operating to direct the evolution of selfing in animals and plants.


Etymology

The term derives from the lat, hermaphroditus, from grc, ἑρμαφρόδιτος, hermaphroditos, which derives from
Hermaphroditus In Greek mythology, Hermaphroditus or Hermaphroditos (; grc, Ἑρμαφρόδιτος, Hermaphróditos, ) was a child of Aphrodite and Hermes. According to Ovid, he was born a remarkably handsome boy whom the naiad Salmacis attempted to rape a ...
(Ἑρμαφρόδιτος), the son of
Hermes Hermes (; grc-gre, Ἑρμῆς) is an Olympian deity in ancient Greek religion and mythology. Hermes is considered the herald of the gods. He is also considered the protector of human heralds, travellers, thieves, merchants, and orator ...
and
Aphrodite Aphrodite ( ; grc-gre, Ἀφροδίτη, Aphrodítē; , , ) is an ancient Greek religion, ancient Greek goddess associated with love, lust, beauty, pleasure, passion (emotion), passion, and procreation. She was syncretized with the Roman god ...
in
Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical co ...
. According to
Ovid Pūblius Ovidius Nāsō (; 20 March 43 BC – 17/18 AD), known in English as Ovid ( ), was a Roman poet who lived during the reign of Augustus. He was a contemporary of the older Virgil and Horace, with whom he is often ranked as one of the t ...
, he fused with the nymph
Salmacis Salmacis ( grc, Σαλμακίς) was an atypical Naiad nymph of Greek mythology. She rejected the ways of the virginal Greek goddess Artemis in favour of vanity and idleness. Mythology Ovid's version Salmacis' attempted rape of Hermaphrodi ...
resulting in one individual possessing physical traits of male and female sexes; Ovid, Metamorphoses, Book IV: The story of Hermaphroditus and Salmacis. according to the earlier
Diodorus Siculus Diodorus Siculus, or Diodorus of Sicily ( grc-gre, Διόδωρος ;  1st century BC), was an ancient Greek historian. He is known for writing the monumental universal history ''Bibliotheca historica'', in forty books, fifteen of which ...
, 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. 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.


Animals


Sequential hermaphrodites

Sequential hermaphrodites (
dichogamy Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...
) occur in
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
in which the individual is born as one sex, but can later change into the opposite sex. This contrasts simultaneous hermaphrodites, in which an individual may possess fully functional male and female genitalia. Sequential hermaphroditism is common in fish (particularly
teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...
fish) and many
gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. Th ...
(such as the common slipper shell), and some flowering plants. Sequential hermaphrodites can only change sex once. Sequential hermaphroditism can best be understood in terms of
behavioral ecology Behavioral ecology, also spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address wh ...
and evolutionary
life history theory Life history theory is an analytical frameworkVitzthum, V. (2008). Evolutionary models of women's reproductive functioning. ''Annual Review of Anthropology'', ''37'', 53-73 designed to study the diversity of life history strategies used by differen ...
, 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: * Protandry: Where an organism is born as a male, and then changes sex to a female. ** Example: The
clownfish Clownfish or anemonefish are fishes from the subfamily Amphiprioninae in the family Pomacentridae. Thirty species of clownfish are recognized: one in the genus '' Premnas'', while the remaining are in the genus '' Amphiprion''. In the wild, ...
(genus '' Amphiprion'') are colorful reef fish found living in
symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasi ...
with
sea anemone Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the '' Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria ...
s. Generally one anemone contains a 'harem', consisting of a large female, a smaller reproductive male, and even smaller non-reproductive males. If the female is removed, the reproductive male will change sex and the largest of the non-reproductive males will mature and become reproductive. It has been shown that fishing pressure can change when the switch from male to female occurs, since fishermen usually prefer to catch the larger fish. The populations are generally changing sex at a smaller size, due to
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Char ...
. * Protogyny: Where the organism is born as a female, and then changes sex to a male. ** Example:
Wrasse The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 81 genera, which are divided into 9 subgroups or tribes. They are typically small, most of them l ...
s (Family Labridae) are a group of reef fish in which protogyny is common. Wrasses also have an uncommon life history strategy, which is termed diandry (literally, two males). In these species, two male morphs exists: an initial phase male and a terminal phase male. Initial phase males do not look like males and spawn in groups with females. They are not territorial. They are, perhaps, female mimics (which is why they are found swimming in group with females). Terminal phase males are territorial and have a distinctively bright coloration. Individuals are born as males or females, but if they are born males, they are not born as terminal phase males. Females and initial phase males can become terminal phase males. Usually, the most dominant female or initial phase male replaces any terminal phase male when those males die or abandon the group. *Bidirectional sex changers: Where an organism has female and male reproductive organs, but act as either female or male during different stages in life. **Example: '' Lythrypnus dalli'' (Family Lythrypnus) are a group of
coral reef fish Coral reef fish are fish which live amongst or in close relation to coral reefs. Coral reefs form complex ecosystems with tremendous biodiversity. Among the myriad inhabitants, the fish stand out as colourful and interesting to watch. Hundreds ...
in which bidirectional sex change occurs. Once a social hierarchy is established a fish changes sex according to its social status, regardless of the initial sex, based on a simple principle: if the fish expresses subordinate behavior then it changes its sex to female, and if the fish expresses dominant or not subordinate behavior then the fish changes its sex to male. Dichogamy can have both conservation-related implications for humans, as mentioned above, as well as economic implications. For instance,
grouper Groupers are fish of any of a number of genera in the subfamily Epinephelinae of the family Serranidae, in the order Perciformes. Not all serranids are called "groupers"; the family also includes the sea basses. The common name "grouper" is ...
s 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.


Simultaneous hermaphrodites

A simultaneous (or synchronous) hermaphrodite (or homogamous) is an adult organism that has both male and female sexual organs at the same time. Simultaneous hermaphrodites can be regarded as both sexes present in the same individual.
Self-fertilization Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species ...
often occurs. * Reproductive system of gastropods:
Pulmonate Pulmonata or pulmonates, is an informal group (previously an order, and before that a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includ ...
land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial gastropod mollusks that have shells (those without shells are kn ...
s and land
slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a smal ...
s are perhaps the best-known kind of simultaneous hermaphrodite, and are the most widespread of terrestrial animals possessing this sexual polymorphism. Sexual material is exchanged between both animals via
spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...
, which can then be stored in the
spermatheca The spermatheca (pronounced plural: spermathecae ), also called receptaculum seminis (plural: receptacula seminis), is an organ of the female reproductive tract in insects, e.g. ants, bees, some molluscs, oligochaeta worms and certain other ...
. After exchange of
spermatozoa A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, ...
, both animals will lay fertilized eggs after a period of gestation; then the eggs will proceed to hatch after a development period. Snails typically reproduce from early spring through late autumn. * :Banana slugs are another example of a hermaphroditic gastropod. Mating with a partner is more desirable biologically, as the genetic material of the resultant offspring is varied, but if mating with a partner is not possible, self-fertilization is practiced. The male sexual organ of an adult banana slug is quite large in proportion to its size, as well as compared to the female organ. It is possible for banana slugs, while mating, to become stuck together. If a substantial amount of wiggling fails to separate them, the male organ will be bitten off (using the slug's
radula The radula (, ; plural radulae or radulas) is an anatomical structure used by molluscs for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food ...
), see apophallation. If a banana slug has lost its male sexual organ, it can still mate as a female, making its hermaphroditic quality a valuable adaptation. * The species of colourful sea slugs '' Goniobranchus reticulatus'' is hermaphroditic, with both male and female organs active at the same time during copulation. After mating, the external portion of the penis detaches, but is able to regrow within 24 hours. *
Hamlets A hamlet is a human settlement that is smaller than a town or village. Its size relative to a parish can depend on the administration and region. A hamlet may be considered to be a smaller settlement or subdivision or satellite entity to a lar ...
, unlike other fish, seem quite at ease mating in front of divers, allowing observations in the wild to occur readily. They do not practice self-fertilization, but when they find a mate, the pair takes turns between which one acts as the male and which acts as the female through multiple matings, usually over the course of several nights. *
Earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...
s are another example of a simultaneous hermaphrodite. Although they possess ovaries and testes, they have a protective mechanism against self-fertilization. Sexual reproduction occurs when two worms meet and exchange
gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
s, copulating on damp nights during warm seasons. Fertilized eggs are protected by a cocoon, which is buried on or near the surface of the ground. * The free-living hermaphroditic nematode '' Caenorhabditis elegans'' reproduces primarily by self-fertilization, but infrequent out-crossing events occur at a rate of approximately 1%. * The mangrove killifish (''
Kryptolebias marmoratus The mangrove killifish or mangrove rivulus, ''Kryptolebias marmoratus'' ( syn. ''Rivulus marmoratus''), is a species of killifish in the family Rivulidae. It lives in brackish and marine waters (less frequently in fresh water) along the coasts o ...
'') is a species of fish that lives along the east coast of North, Central and South America. These fish are simultaneous hermaphrodites. ''K. marmoratus'' produces eggs and sperm by meiosis and routinely reproduces by self-fertilization. Each individual hermaphrodite normally fertilizes itself when an egg and sperm produced by an internal organ unite inside the fish's body. This species is also regarded as the only known vertebrate species that can reproduce by self fertilization.


Pseudohermaphroditism

When
spotted hyena The spotted hyena (''Crocuta crocuta''), also known as the laughing hyena, is a hyena species, currently classed as the sole extant member of the genus ''Crocuta'', native to sub-Saharan Africa. It is listed as being of least concern by the IUC ...
s were first scientifically observed 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. It can be difficult to determine the sex of wild spotted hyenas until
sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definitio ...
, 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.


Plants

Hermaphrodite is used in
botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...
to describe, for example, a
flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...
that has both staminate (male, pollen-producing) and
carpel Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils ...
late (female, ovule-producing) parts.


Monoecy

Flowering plant species with separate male and female flowers on the same individual are called
monoecious Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is con ...
. Monoecious plants are often referred to as hermaphroditic because they produce both male and female gametes. However, the individual flowers are not hermaphroditic because they are only one sex. Monoecy only occurs in about 7% of
angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants t ...
species. Conifers are almost all monoecious, but 65% of gymnosperm species are dioecious. Some plants can change their sex throughout their lifetime. This process is called
Sequential hermaphroditism Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...
.


Andromonecy

In andromonecious species, the plants produce perfect (hermaphrodite) flowers and separate staminate flowers that function as male but are sterile as female. Andromonecy occurs in about 4000 species of flowering plants (2% of flowering plants).


Use regarding humans

Historically, the term hermaphrodite was used in law to refer to people whose sex was in doubt. The 12th-century ''
Decretum Gratiani The ''Decretum Gratiani'', also known as the ''Concordia discordantium canonum'' or ''Concordantia discordantium canonum'' or simply as the ''Decretum'', is a collection of canon law compiled and written in the 12th century as a legal textbook b ...
'' states that "Whether an hermaphrodite may witness a testament, depends on which sex prevails" ("Hermafroditus an ad testamentum adhiberi possit, qualitas sexus incalescentis ostendit."). Similarly, the 17th-century English jurist and judge
Edward Coke Edward is an English given name. It is derived from the Anglo-Saxon name ''Ēadweard'', composed of the elements '' ēad'' "wealth, fortune; prosperous" and '' weard'' "guardian, protector”. History The name Edward was very popular in Anglo-Sa ...
(Lord Coke), wrote in his '' Institutes of the Lawes of England'' on laws of succession stating, "Every heire is either a male, a female, or an hermaphrodite, that is both male and female. And an hermaphrodite (which is also called ''Androgynus'') shall be heire, either as male or female, according to that kind of sexe which doth prevaile." During the
Victorian era In the history of the United Kingdom and the British Empire, the Victorian era was the period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian period and preceded the Edwardi ...
, medical authors attempted to ascertain whether or not humans could be hermaphrodites, adopting a precise biological definition to the term. From that period until the early 21st century, intersex individuals were termed true hermaphrodites if their
gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
al tissue contained both testicular and ovarian tissue, or pseudohermaphrodites if their external appearance (
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...
) differed from sex expected from internal gonads. This language has fallen out of favor due to misconceptions and pejorative connotations associated with the terms, and also a shift to nomenclature based on genetics. The term intersex describes a wide variety of combinations of what are considered male and female biological characteristics. Intersex biology may include, for example, ambiguous-looking external genitalia,
karyotype A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...
s 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 Disorders of sex development (DSDs), also known as differences in sex development, diverse sex development and variations in sex characteristics (VSC), are congenital conditions affecting the reproductive system, in which development of chromo ...
, a term vigorously contested. This is particularly because of a relationship between medical terminology and medical intervention. Intersex civil society organizations, and many human rights institutions, have criticized medical interventions designed to make intersex bodies more typically male or female. In some cases, intersex traits are caused by unusual levels of sex hormones, which may be the result of an atypical set of sex chromosomes. One possible pathophysiological explanation of intersex in humans is a
parthenogenetic Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
division of a haploid ovum into two haploid ova. Upon fertilization of the two ova by two sperm cells (one carrying an
X chromosome The X chromosome is one of the two sex-determining chromosomes ( allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex ...
and the other carrying a
Y chromosome The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or abse ...
), 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
testis-determining factor Sex-determining region Y protein (SRY), or Testis-determining factor (TDF), is a DNA-binding protein (also known as gene-regulatory protein/transcription factor) encoded by the ''SRY'' gene that is responsible for the initiation of male sex de ...
(SRY) from the Y chromosome to the X chromosome during
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
. The SRY is then activated in only certain areas, causing development of
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testost ...
in some areas by beginning a series of events starting with the upregulation of the
transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...
(SOX9), and in other areas not being active (causing the growth of ovarian tissues). Thus,
testicular A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...
and ovarian tissues will both be present in the same individual. Fetuses before sexual differentiation are sometimes described as female by doctors explaining the process. This is not technically true. Before this stage, humans are simply undifferentiated and possess a
paramesonephric duct Paramesonephric ducts (or Müllerian ducts) are paired ducts of the embryo that run down the lateral sides of the genital ridge and terminate at the sinus tubercle in the primitive urogenital sinus. In the female, they will develop to form the fa ...
, a
mesonephric duct The mesonephric duct (also known as the Wolffian duct, archinephric duct, Leydig's duct or nephric duct) is a paired organ that forms during the embryonic development of humans and other mammals and gives rise to male reproductive organs. Struc ...
, and a
genital tubercle A genital tubercle or phallic tubercle is a body of tissue present in the development of the reproductive system. It forms in the ventral, caudal region of mammalian embryos of both sexes, and eventually develops into a primordial phallus. In t ...
.


Evolution

The evolution of
anisogamy Different forms of anisogamy: A) anisogamy of motile cells, B) egg_cell.html"_;"title="oogamy_(egg_cell">oogamy_(egg_cell_and_sperm_cell),_C)_anisogamy_of_non-motile_cells_(egg_cell_and_spermatia)..html" ;"title="egg_cell_and_sperm_cell.html" ;" ...
may have contributed to the evolution of simultaneous hermaphroditism and sequential hermaphroditism but, as of 2016 it remains unclear if the evolution of anisogamy first led to hermaphroditism or gonochorism. It is possible that hermaphroditism evolved from gonochorism, or vice versa. Most studies on its evolution focus on plants, and its evolution in animals is unclear . Simultaneous hermaphroditism that exclusively reproduces through self-fertilization has evolved many times in plants and animals, but it might not last long evolutionarily.


In animals

Joan Roughgarden and Priya Iyer argued that the last common ancestor for animals was hermaphroditic and that transitions from hermaphroditism to gonochorism were more numerous than the reverse. However, their argument was based on
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
Spiralia The Spiralia are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa. The term ''Spiralia'' is applied to those phyla that exhibit canonical spiral cleavage ...
, assignments of sexual modes for the
phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclatur ...
level than the species level, and methods exclusively based on maximum parsimony. Hermaphroditism is
polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...
in invertebrates where it evolved from gonochorism and gonochorism is also ancestral to hermaphroditic fishes. According to Nelson Çabej simultaneous hermaphroditism in animals most likely evolved due to a limited number of mating partners.


In plants

It is widely accepted that the first
vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...
s were outcrossing hermaphrodites. In flowering plants, hermaphroditism is ancestral to dioecy. Flowers in angiosperms evolved to attract insects as vectors for
pollination Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, ...
. Hermaphroditism in plants may promote self fertilization in pioneer populations. However, plants have evolved multiple different mechanisms to avoid self-fertilization in hermaphrodites, including
sequential hermaphroditism Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...
, molecular recognition systems and mechanical or morphological mechanisms such as
heterostyly Heterostyly is a unique form of polymorphism and herkogamy in flowers. In a heterostylous species, two or three morphological types of flowers, termed "morphs", exist in the population. On each individual plant, all flowers share the same morp ...
.


See also

*
Asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...
*
Trioecy Trioecy, or subdioecy, is a rare sexual system characterized by the coexistence of males, females, and hermaphrodites. It has been found in both plants and animals. Trioecy is sometimes referred to as a mixed mating system alongside androdioecy an ...
*
Androgyny Androgyny is the possession of both masculine and feminine characteristics. Androgyny may be expressed with regard to biological sex, gender identity, or gender expression. When ''androgyny'' refers to mixed biological sex characteristics in ...
*
Gonochorism In biology, gonochorism is a sexual system where there are only two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric. Gonochorism c ...
* Gynandromorph *
Self-pollination Self-pollination is a form of pollination in which pollen from the same plant arrives at the stigma of a flower (in flowering plants) or at the ovule (in gymnosperms). There are two types of self-pollination: in autogamy, pollen is transferred to ...
*
Self-fertilization Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species ...
* Futanari *
Non-binary gender Non-binary and genderqueer are umbrella terms for gender identities that are not solely male or femaleidentities that are outside the gender binary. Non-binary identities fall under the transgender umbrella, since non-binary people typicall ...


References


Further reading

* * Discovery Health Channel, (2007) "I Am My Own Twin" * * * * , reprinted in: * *


External links


Britannica Online Encyclopedia: hermaphroditism (biology)

Current Biology – Gender trading in a hermaphrodite

The Evolution of Self-Fertile Hermaphroditism: The Fog Is Clearing

"Born True Hermaphrodite – Pictorial Profile", about Lynn Edward Harris
{{Authority control Sexual reproduction Reproductive system Intersex in history Supernumerary body parts