Upon fertilization of the two ova by two sperm cells (one carrying an X 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.
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, and also a shift to nomenclature based on genetics.
Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates. 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 preferred usage for humans, since the word hermaphrodite is considered to be misleading and stigmatizing, Since the estimated total number of animal species is 8.6 million, the percentage of animal species that are hermaphroditic is about 0.7%.
Hermaphrodite is used in older literature to describe any person whose physical characteristics do not neatly fit male or female classifications, but the term has been replaced by intersex.Sequential hermaphroditism is common in fish (particularly teleost fish) and some jellyfish, many gastropods (such as the common slipper shell), and some flowering plants.Sequential hermaphrodites can only change sex once.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.which derives from Hermaphroditus (Ἑρμαφρόδιτος), the son of Hermes and Aphrodite in Greek mythology.A closer analogy to hermaphroditism in botany is the presence of separate male and female flowers on the same individual—such plants are called monoecious.