ANDREJ ISAKOVIC/AFP/Getty ImagesĪre the biological causes of sexual orientation different for men than they are for women? People carry rainbow flags during the Gay Pride parade on Septemin Belgrade, Serbia. A lot of parents worry they may have influenced their child's sexual orientation, but we have been able to rule out that part of the environment. The one thing that we reliably know is that your family did not cause this. There has been interest in the fraternal birth order effect, the fetal environment, the hormonal character of the placenta, the way levels of maternal stress may influence the fetal environment and may change the hormonal milieu, but there's been no reliable evidence. We've looked at a bunch of things, but we haven't been able to nail it down. There is clearly something non-genetic going on. In other words, genetics raises the chances of you being gay, but it doesn't finish the job. If sexual orientation was completely governed by genes, then heritability would be 100 percent. So if we look at the population of Americans and all of their sexual orientations, the estimate of 30 to 40 percent means that amount of the person to person variation in sexual orientation is due to genetic factors. Heritability is not about a person heritability is always about a population. The current evidence really focuses on twin studies, and these studies suggest that the heritability of sexual orientation ranges between 30 and 40 percent. There was a lot of research in the '90s where people were hoping to find a genetic marker that didn't go too well. All geneticists know that no complex human behaviors are determined by single genes. Probably the strongest current evidence is for genetic contributions-but that doesn't mean we've found a gene. What do we actually know? How much of a person's sexual orientation can be chalked up to biology? This interview has been condensed and lightly edited.
She spoke with Newsweek about what she and her colleagues in the field know-and what they don't-about how a person's sexual orientation might form. Recently, scientists announced that they found some genes that might be associated with sexual orientation and a biological explanation for the reason gay men tend to have older brothers.īut the field of sexual orientation research is far broader and more complicated than two studies-and Lisa Diamond, a psychologist and sexual orientation researcher at the University of Utah, knows that better than most.