Nutt says now is an exciting time for researchers interested in the brain. For instance, they are discovering many new things about the genetic and neurophysiological aspects of homosexuality. Studies have shown that men born to women who are experiencing stress early in their pregnancies are more likely to be gay as adults than men born to women who are not stressed during this period of development. The culprit is a testosterone-like hormone called androstenedione. It disrupts the amount of testosterone the fetal brain receives and the time at which the brain receives it, which affects the development of the part of the brain that is linked to sexual orientation. Many studies of transgender brains are telling as well. Several parts of the brain in males who identify as females look more similar to those of females than they do to those of males.

Nicole says she doesn’t think she could be a boy because she has never known what it feels like to be one. Likewise, Jonas says he has never known what it’s like to have a brother because he’s always known his twin as a sister. Their parents still wonder how identical twins with identical DNA could be so different.