Are There Genes for Gender Identity?

Scientists and sociologists have argued for centuries over which influences people's personalities more: nature (genetics) or nurture (upbringing and cultural context).

Contemporary feminist theory holds that, excluding biological sex characteristics, all "masculine" or "feminine" behavior is the product of culture. In the 1980s, Candace West and Don Zimmerman coined the term "doing gender" -- acting in accordance with male or female behavioral norms. A woman who uses flirtatious mannerisms, according to this theory, is doing so not as a result of genetics, but rather because she's performing feminism to fit in with social norms -- because of her nurture.

But a recent study of male-to-female transsexuals -- people who have male genitalia but self-identify as females -- isolated a genetic peculiarity in its subjects.

A transsexual is a person who does not identify with his or her biological sex. A male-to-female transsexual was born with male genitalia but self-identifies as a woman; a female-to-male transsexual was born with female genitalia but self-identifies as a man.

In October 2008, researchers at several universities published a study where they had compared DNA samples from 112 Australian and American male-to-female transsexuals with samples from 250 typical men. The research -- led by Vincent Harley of Prince Henry's Institute in Melbourne, Australia -- focused on three genes encoding sex hormones. One of these three, the androgen receptor gene, was longer in transsexual subjects than in non-transsexual controls. The significance?

A longer androgen receptor gene could reduce testosterone during brain development, a hormone vital for male sex characteristics and behavior. So if male-to-female transsexuals have longer androgen receptor genes, they might have less testosterone, the precursor to their female self-identification. If this biological explanation is true across the board, it argues against the possibility that transsexualism has no basis in genetics.

Harley's study indicates that gender identity could have genetic roots, but it is important to keep these findings in perspective. First, the sample size -- at a little over 100 subjects -- was fairly small. Second, the study only examined three genes. And third, it would be imprudent to extrapolate from a study of a very specific subject group (male-to-female transsexuals) to make broader theorizations about gender identity without examining other populations. Similar to research on homosexuality genetics, it is not conclusive, but it does raise some interesting questions and opportunities for future research.