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.