Dr. Dean Hamer is a geneticist, author of several books including The Science of Desire and The God Gene, and a filmmaker. In this episode, we talk about Dean’s background in genetics and how the science of sexual orientation helped shape the “born this way” movement in gay civil rights. We talk about ethical debates surrounding the biological study of sexual orientation, and why it should be prioritized, and examine various evolutionary, genetic, hormonal, and neurological theories for sexual orientation. We talk about the role of prenatal sex hormones, fraternal birth order, the maternal immune hypothesis, the evolutionary gay uncle hypothesis, antagonistic pleiotropy, and more. We also discuss connections between sexual attraction and philosophy of mind, sex differences in sex drive, animal research on mating psychology, and more. Lastly, we talk about Dean’s recent work on gender and sexuality in the Pacific Islands, cultural anthropology documenting gender and sexual diversity across history, and how to best approach ethical discussion and research on sensitive topics related to sex and gender.