There are several atypical gender identities, that is, gender identities that do not correspond to the much more common ones, man, woman, boy, and girl. Gender identities are, primarily, determined by whether the individuals in question consider themselves to be boys, girls, men, women, or something else.
The sex of an individual is generally determined by examining one's external genitalia. Most of the time this method is adequate, but sometimes the differentiation of one's external genitalia have been influenced by abnormal hormone levels while still in the womb, or some other changes have occurred that create incongruencies among chromosomal factors, internal genitalia, and/or external genitalia. In such cases, the sex of the individual may be ambiguous. When hormonal abnormalities influence pre-natal formation of the body of an individual whose chromosomal nature (XY) would ordinarily produce a person with male genitalia, that person will may be born with female external genitalia. Similarly a chromosomally female (XX) fetus can be masculined and may be born with external genitalia that appear to be male. Sometimes hormonal influences are of an intermediate strength and the body of the individual is ambiguous. It may be impossible to determine by examination of external features whether the baby in question is an XX female who has been masculinized to some extent, or an XY male who has been feminized to some extent. There are also individuals who have other chromosomal combinations (XXY, XYY, etc.) as well as individuals whose bodies may contain approximately equal numbers of XX cells and XY cells and who may have both male genitalia and female genitalia. Arbitrarily designating these individuals as boys, girls, men, or women would serve to deceive all people involved concerning the realities of gender identity and gender role of these people.
In addition to the physical ambiguities and combinations, there are also mental characteristics that appear to be strongly influenced by hormone levels at certain critical times in fetal development. This phenomenon is very clearly understood in the case of cattle because a fairly frequent mishap in gestation produces a freemartin (unconventional heifer), a cow that is female in respect of its genitalia but one that behaves sexually like a bull.
Post-natal condition may also strongly influence the self image by which a person categorizes and understands himself or herself.
If one's chromosomal status is XX, if that person's period in the womb is normal and as a baby has normal female genitalia, and if that person is raised as are other female children in that culture, then that individual will almost certainly say that she is a girl, and later she will say that she is a woman. To that extent that nothing puts her strongly at odds with her society, she will probably take up an ordinary gender role rather than doing something unusual like becoming a knight in armor.
If one's chromosomal status is XY, if that person's gestation is normal and the genitalia are typical of males, and if that person is raised as are other male children in that culture, then that individual will almost certainly say that he is a boy, and later he will say that he is a man. If nothing puts him strongly at odds with his society, the chances are that he will follow the pursuits that are common among other men in his culture rather than, e.g., try to function as an escort for lonely heterosexual males.
But what will be the gender identity of someone who does not fulfill these ordinary expectations? Chromosomal differences may have profound behavioral and/or reproductive consequences. Hormonal differences during gestation may have effects on external genitalia, sexual motivation, and/or other behavioral characteristics. Post-natal conditioning may have easily recognizable effects on the behavior and motivations of individuals.
The gender identity that each individual possesses is unique. Individuals act out their gender identities as gender roles. Other people then observe their gender role dress, behavior, and other such indications, and infer the gender identity and the sex of these individuals. If everything were as simple as language paints it, then there would be only XX and XY individuals, XX individuals would all call themselves girls and then women and mean exactly the same thing in every case, and they would take up a standard gender role from which other people could unfailingly infer their gender identity and their sex. Similarly, XY individuals would be unambiguously male in all the external signals they give off, and other people in the society could infallibly infer their gender identities and sex from those public signals. Reality, however, is far from being that simple.
(This article is "in process". Examples, etc., to follow.
