"A comprehensive, engaging and occasionally quite funny look at the current state of the research on the topic." -- Schuyler Velasco, Salon

"A clear and comprehensive summary of recent studies of sexual orientation--a review that should be useful to lay people and journalists as well as to professionals in the field. LeVay has a knack for describing complicated scientific topics--brain anatomy, behavior genetics, endocrinology, cognitive psychology--in straight-forward and easy-to-understand ways." -- Richard Lippa, Sex Roles

What causes a child to grow up gay or straight? In this 2017 book, neuroscientist Simon LeVay summarizes a wealth of scientific evidence that points to one inescapable conclusion: Sexual orientation results primarily from an interaction between genes, sex hormones, and the cells of the developing body and brain.

LeVay helped create this field in 1991 with a much-publicized study in Science, where he reported on a difference in the brain structure between gay and straight men. Since then, an entire scientific discipline has sprung up around the quest for a biological explanation of sexual orientation. In this book, LeVay provides a clear explanation of where the science stands today, taking the reader on a whirlwind tour of laboratories that specialize in genetics, endocrinology, neuroscience, cognitive psychology, evolutionary psychology, and family demographics. The Second Edition updates all the science, and adds a new chapter, 'Beyond Gay and Straight,' that delves into all the subtleties of sexual orientation that are not captured in a simply gay-straight dichotomy.

Although many details remain unresolved, the general conclusion is clear: A person’s sexual orientation arises in large part from biological processes that are already underway before birth. LeVay also makes it clear that these lines of research have a lot of potential because, far from seeking to discover “what went wrong” in the lives of gay people, attempting to develop “cures” for homosexuality, or returning to traditional explanations that center on parent-child relationships, various forms of “training,” or early sexual experiences, modern scientists are increasingly seeing sexual variety as something to be valued, celebrated, and welcomed into society.

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