In August 1991 a neurologist announced the finding of a physiological difference between the brains of heterosexuals & homosexuals. This was science that not only challenged accepted beliefs but carried profound legal, political, & social implications. Two years later a team of geneticists reported finding a likely genetic basis for homosexuality in men. This book explores the rich & varied research that is currently being carried out in neurobiology, endocrinology, & genetics. It also considers the awesome ramifications of research that may well come to explain the origins of one of the fundamental components of our humanity.