Intersexuality (hermpahroditism) is a natural human state. We are all conceived with the potential to develop into either sex. The embryonic developmental default is female. A series of triggers during the first weeks of pregnancy places the fetus on the path to maleness.
In rare cases, some women have a male's genetic makeup (XY chromosomes) and vice versa. But, in the vast majority of cases, one of the sexes is clearly selected. Relics of the stifled sex remain, though. Women have the clitoris as a kind of symbolic penis. Men have breasts (mammary glands) and nipples.
The Encyclopedia Britannica 2003 edition describes the formation of ovaries and testes thus:
"In the young embryo a pair of gonads develop that are indifferent or neutral, showing no indication whether they are destined to develop into testes or ovaries. There are also two different duct systems, one of which can develop into the female system of oviducts and related apparatus and the other into the male sperm duct system. As development of the embryo proceeds, either the male or the female reproductive tissue differentiates in the originally neutral gonad of the mammal."
Yet, sexual preferences, genitalia and even secondary sex characteristics, such as facial and pubic hair are first order phenomena. Can genetics and biology account for male and female behavior patterns and social interactions ("gender identity")? Can the multi-tiered complexity and richness of human masculinity and femininity arise from simpler, deterministic, building blocks?
Sociobiologists would have us think so.
For instance: the fact that we are mammals is astonishingly often overlooked. Most mammalian families are composed of mother and offspring. Males are peripatetic absentees. Arguably, high rates of divorce and birth out of wedlock coupled with rising promiscuity merely reinstate this natural "default mode", observes Lionel Tiger, a professor of anthropology at Rutgers University in New Jersey. That three quarters of all divorces are initiated by women tends to support this view.
Furthermore, gender identity is determined during gestation, claim some scholars.
Milton Diamond of the University of Hawaii and Dr. Keith Sigmundson, a practicing psychiatrist, studied the much-celebrated John/Joan case. An accidentally castrated normal male was surgically modified to look female, and raised as a girl but to no avail. He reverted to being a male at puberty.
His gender identity seems to have been inborn (assuming he was not subjected to conflicting cues from his human environment). The case is extensively described in John Colapinto's tome "As Nature Made Him: The Boy Who Was Raised as a Girl".