Discussing British Channel 4 TV's current series, The Secret Life of 5-Year-Olds, a correspondent writing to The Daily Telegraph (3rd Feb., p. 17) remarks that, in order for social scientists to settle the question of whether nature or nurture determines sexual identity, you would have "to breed children in test tubes, transfer them to artificial wombs, consign them to nurseries at birth, give them ‘gender’ non-specific names, clothe them identically, and treat them exactly the same…” etc.

C.Badcock/Wikimedia commons
Source: C.Badcock/Wikimedia commons

As the same correspondent remarks, it all sounds like Brave New World fiction, but in fact Nature has carried out the closest we are ever likely to get to such an experiment in two very different places: the Dominican Republic and Papua New Guinea, thanks to a rare genetic disorder (5α-reductase deficit) whose effect is to cause normal XY males to be born with seemingly female genitals (left). However, at puberty, normal male development takes place.

A study of this form of pseudo-hermaphroditism in the Dominican Republic found 18 cases, all of whom had been unambiguously assigned a female sex and socialized as girls by parents who had no idea that their daughters might be sons. This occurred in a traditional, rural, unsophisticated, Latin American society with clear and distinct differences in male and female sex role behaviour. At the time of their sex change, several of the subjects were already engaged to be married to men. All had girls’ names, dressed as girls, and regarded themselves as girls until the sex change.

Following puberty, all the subjects developed male genitals along with the other secondary sexual characteristics of adolescent males. One of the first signs of the sex change in the erstwhile girls was a sudden interest in playing football! The ages at which subjects first experienced morning erections, nocturnal emissions, masturbation and sexual intercourse were not appreciably different between those raised as girls who changed to a male-gender identity and a control group raised as boys from the beginning.

The study found that all but two (89 per cent) made a full sex-role change and were living with women at the time of the study despite parental consternation, their own initial shock, and social pressure not to do so. One of the remaining two continued to dress as a woman, had sexual relations with women but not men, and had masculine ways. The other persisted in the female role and lived with a man for a year until he left her. She was described by the study as having masculine build and mannerisms but wore false breasts and at the time of the study desired a sex change operation to make her a more normal woman. Of the 18, she was the only one who persisted in all respects with the female sex role that she had been assigned at birth. The researchers conclude: “These subjects demonstrate that in the absence of sociocultural factors that could interrupt the natural sequence of events, the effect of testosterone predominates, over-riding the effect of rearing as girls.”

The Simbari Anga of Papua New Guinea have a radically different culture from that of the Dominican Republic: after male initiation rites (prior to puberty) the two sexes are kept rigorously separate, and ritualized oral sex occurs between men from puberty until premarital age. Yet in spite of this barrier between the sexes,

most of the affected individuals changed their gender identities from female to male at puberty, albeit with much turmoil … The fact that these individuals adopted male gender identity at puberty suggests that prenatal exposure of the brain to testosterone, combined with normal activational events of male puberty, overrides any effect of rearing in the determination of adult gender identity.

The researchers conclude:

It has been proposed that gender identity becomes fixed by 18 months to 4 years of age, at the approximate time of language development (…). During this time a child becomes aware of his or her gender. Awareness of one’s gender and being unalterably fixed in that gender appear to be two separate issues. Subjects with 5α-reductase deficiency who have undergone a gender change suggest that gender identity in man is not fixed in childhood but is continually evolving, becoming fixed with or following pubertal events.

In humans, androgens, and not just environmental or sociocultural factors, make a strong and definite contribution to the formation of a male gender identity (…). 

In terms of the diametric model, sexuality is a complex issue, as I argued in a previous post, with a real, mechanistic, genetically-determined part—sex—and an imaginary, mentalistic part—gender. Furthermore, as I also pointed out in another post, even the purely genetic/hormonal aspect of sex is much more complicated in reality than it might seem. But however you look at it, the score seems to be: Nature 9, Nurture 1!

References

Imperato-McGinley, J., et al., Androgens and the Evolution of Male-gender Identity among Male pseudohermaphrodites with a 5a-reductase Deficiency. New England Journal of Medicine, 1979. 300 (22): p. 1233-37.

Imperato-McGinley, J., et al., A cluster of male pseudohermaphrodites with 5a-reductase deficiency in Papua New Guinea. Clinical Endocrinology, 1991. 34: p. 293-8.

LeVay, S., The Sexual Brain, 1993, Cambridge, Mass.: The MIT Press. p. 168.

Imperato-McGinley, J., & Zhu, Y.-S. (2002). Androgens and male physiology the syndrome of 5α-reductase-2 deficiency, Molecular and Cellular Endocrinology, 198(1-2), 51-59. doi:http://dx.doi.org/10.1016/S0303-7207(02)00368-4.

Be sure to read the following responses to this post by our bloggers:

Margaret Mead and the Great Samoan Nurture Hoax is a reply by Christopher Badcock Ph.D.

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