In 1871, Charles Darwin published Descent of Man and Selection in Relation to Sex, a text that extended, elaborated and completed his On the Origin of Species (1859). When he had published Origin, Darwin sought, albeit unsuccessfully, to skirt controversy; in Descent he waded into the fray on near-innumerable issues. Readers could find explicit the claim that humans had descended from apes, in addition to explorations of the similarities and apparent gulfs between ‘man’ and other animals. They also found Darwin's opinions on issues ranging from the origin and hierarchy of races to the question of women's education, from the source of altruistic bravery to the biological importance of aesthetic judgement, from his views on what his cousin would term ‘eugenics’ to the history of monogamy. In the last 150 years these ideas have been variously contested, rejected and recovered, so that the shadow of Descent extended into debates over the development of languages, the evolution of human sexualities, the ongoing possibilities of eugenics and the question of women's equality. In this volume, appearing during the sesquicentennial of the text's first appearance, one finds papers dedicated to all of these themes and more, laying out the roots and fruits of Darwin's Descent.

Charles Darwin's Descent of Man was suffused with questions of courtship, mating and sex. Following in his footsteps, biologists throughout the twentieth century interrogated the sexual behaviour of humans and animals. This paper charts the fate of evolutionary theories of sexuality to argue that – despite legal and social gains of the past century – when biologists used sexual selection as a tool for theorizing the evolution of homosexual behaviour (which happened only rarely), the effect of their theories was to continuously reinscribe normative heterosexuality. If, at the end of the nineteenth century, certain sex theorists viewed homosexuality as a marker of intermediate sex, by the late twentieth a new generation of evolutionary theorists idealized gay men as hyper-masculine biological males whose sexual behaviours were uncompromised by the necessity of accommodating women's sexual preferences. In both cases, normative assumptions about gender were interwoven with those about sexuality. By the twenty-first century, animal exemplars were again mobilized alongside data gathered about human sexual practices in defence of gay rights, but this time by creating the opportunity for naturalization without recourse to biological determinism.