To argue that homosexuality is a spoke in the great wheel of human evolution is to assert that its origins are ultimately biological. Unfortunately, this assertion immediately plunges us into bitter controversy. While there are many theories, a great and unfortunate chasm lies between biological and social accounts of homosexuality and theorising is polarised into two antagonistic camps. On one side are social constructivists who see homosexuality as an acquired or constructed behaviour, part of our repertoire of sexual roles. On the other are essentialists who feel homosexuality is genetically programmed. It is useless to note, as Symons (1979) does, that the evolutionary theorist deliberately avoids taking sides in the nature/nurture debate, which is about how behaviour develops rather than why it does; the debate is too bitter and polarised. This classic divide lies at the heart of much social theorising but unlike other topics there are few integrationist theories of homosexual causation in the middle ground.