TWO things are clear about human sexual orientation. First, it is biological; second, it is complex. Sexual behaviour, identity, attractions and fantasies don’t line up neatly. Consistently, biologists fail to recognise this.
In their 1948 book
Sexual Behavior in the Human Male, Alfred Kinsey and his collaborators showed how male sexuality varies smoothly, from a majority identifying as completely heterosexual to a minority who identify as gay. Men “do not represent two discrete populations, heterosexual and homosexual”, wrote Kinsey. “The world is not to be divided into sheep and goats.” He concluded the same for women five years later.
Biologists often look for factors related to sexual orientation, be they genetic, hormonal or in the brain. It is easier to search for differences between two starkly different groups, so the smooth variation in sexuality Kinsey described collapses to an artificial binary: heterosexual or homosexual, or sometimes heterosexual or non-heterosexual.
How the boundaries of these categories are drawn varies wildly. In some studies, “homosexual” means anyone who identifies as mostly or entirely gay or lesbian; in others, anyone who has had any type of same-sex experience. Bisexual people are either lumped in with gay and lesbian people in a non-heterosexual category or excluded for being “inconsistent”. Women can also be excluded, as female sexuality is often considered too variable.
Why does this all matter? As Rebecca Jordan-Young discussed in her book
Brain Storm a decade ago, by distorting sexual orientation to fit what we assume it is, we risk editing out the most informative data points – and drawing false conclusions.
As an example, take the recent book
The Goodness Paradox by the evolutionary psychologist Richard Wrangham. This is an excellent account of human cognitive evolution, but in a section on homosexuality, Wrangham writes: “Homosexual men also have somewhat feminized face shapes and shorter, lighter bodies than heterosexual men, most likely from relatively low exposure to testosterone in the womb” and “Homosexual men who take a strongly male sexual role, for example, seem less likely to have had low exposure to prenatal testosterone than those taking a more female role.”
Wrangham accepts the findings are “not always consistent”. But the underlying science speaks of small variations between people, not stark contrasts. A recent study in Canada (sample size 863) did find that gay men
are slightly shorter than heterosexual men. Other studies find no difference. A recent detailed analysis of the faces of gay men found a “mosaic of both masculine and feminine features”, and that
independent observers rated gay men as looking more masculine.
As for linking sexual roles in gay men to developmental hormone levels, that requires a long line of causal links through complex, inconsistent and indirect evidence. Increasingly, it looks like the conclusion is too simplistic: another false dichotomy along the lines of
“male” and “female” brains that ignores immense variation within groups.
Ultimately, this issue matters because it isn’t just biologists who divide the world into gay and straight. The science of sexual orientation
informs the law and the societal and self-perception of minority groups.
The persistence of negative stereotypes and discrimination against those of different sexual orientations is precisely why the biological sciences must be careful when studying this area. We need clear, unbiased answers about the biological nature of sexual orientation – even if those answers are complex.