Nature, Nurture, and Sexual Orientation

Our personal assumptions matter, often by influencing our attitudes and public policies. Here’s an example:

  • If you see same-sex attraction as a lifestyle choice, as swayed by social influence, or as encouraged by social tolerance, then you probably are opposed to equal employment and marriage rights for gay people. Those in fact are the prevailing assumptions in the 75 countries that legally forbid homosexual behavior.
  • If you see sexual orientation as “inborn”—as shaped by biological and prenatal environmental influences—then you likely favor “equal rights for homosexual and bisexual people.”

That being so, note Michael Bailey, Paul Vasey, Lisa Diamond, Marc Breedlove, Eric Vilain, and Marc Epprecht, in their state-of-the-art review of sexual orientation research, psychological science has much to offer our public conversation about gay rights issues. Some of their conclusions:

  • The phenomenon: Sexual attraction, arousal, behavior, and identity usually coincide, but not always. For example, some men who identify as straight may nevertheless be strongly attracted to men.
  • Same-sex attraction has existed across time and place. Although sexual identity and behavior are culturally influenced, same-sex activity crosses human history, dating from the era of Mesolithic rock art.
  • Bisexual identity is multifaceted. Some claim bisexual identity after previous sexual experiences with both men and women, or, even if primarily attracted to one sex, because of occasional sexual attractions to the other sex.  “Some bisexual-identified men have bisexual genital arousal patterns and some do not.” With men, bisexuality is more often a transitional identity; with women, it is more often a stable identity.
  • Heritability. Twin studies suggest that “about a third of variation in sexual orientation is attributable to genetic influences.”
  • The nonsocial environment matters. One striking example is the fraternal birth order effect: The odds of a man having a same-sex orientation are about:
    • 2% for those with no older biological brothers.
    • 2.6% given one older biological brother,
    • 3.5% given two older biological brothers,
    • 4.6% given three older biological brothers, and
    • 6.0% given four older biological brothers.
  • The social environment matters little: “There is no good evidence that either [social influence or social tolerance] increases the rate of homosexual orientation.”

If only a mad scientist could pit nature against nurture by changing, at birth, boys into girls. Castrate them as newborns, surgically feminize them, and then raise them as girls. Does such rearing socialize these “girls” into becoming attracted to males?

Such surgical and social gender reassignment did happen between 1960 and 2000 after a number of babies were born with penises that were malformed or severed in surgical accidents. As teaching psychologists are aware, their gender identity was not so easily transformed. As is less well known, report the expert sexuality researchers, in each of seven known cases where sexual orientation was reported, it was predominantly or exclusively an attraction to women. “This is the result we would expect if male sexual orientation were entirely due to nature, and it is the opposite of the result expected if it were due to nurture.”­­

“If one cannot reliably make a male human become attracted to other males by cutting off his penis in infancy and rearing him as a girl, then what other psychosocial intervention could plausibly have that effect?”

With such scientific evidence in mind, conclude the expert researchers, “we urge governments to reconsider the wisdom of legislation that criminalizes homosexual behavior.”