If gender is largely a social construct, then what leads some people’s identities to diverge from the way in which they were socialized? No one really knows. Certainly genes are not the determinants: Children with XY chromosomes who lack receptors for testosterone and thus have feminized anatomy — and are in turn socialized as women — all tend to identify as women, despite that Y chromosome. Nor do hormones seem to be the deciding factor. Children with XX chromosomes who are exposed to large amounts of testosterone in utero do tend to have more gender-ambiguous interests and are slightly more likely to identify as lesbian or bisexual than the population overall, but the majority still grow up to be straight and female-identifying. Meanwhile, the brain may be built to adapt to socialization, but “the evidence for differences in newborn brains is pretty minimal,” says Lise Eliot, author of Pink Brain, Blue Brain.