In 1993 American scientists claimed they had discovered a gay gene. Sexual orientation it seems, is not a choice, disease or faddish whim but a fundamental biological part of who we are. This book examines this claim, looking at the laboratories where researchers are using incredible new technologies to discover what makes us gay of straight. From studies of male rats that ovulate and a species of African animal where the female has a penis, to the political storm surrounding the claim of a gay gene, from a silicon chip of human DNA that could determine the sexual orientation of a foetus in the womb, to a working theory that homosexuality is a genetic/biological condition that is treatable with an antibiotic, the book explores this often ethically ambiguous territory.