The debate over population was an aspect of a general opening up of the question of sexuality, ranging from the issue of genetics to the broader problem of the nature of sexuality itself, and its complex impact on social life. Though much more muted in Britain than in countries such as Germany, France or the USA the result was, nevertheless, a significant expansion of writings on sexuality in the late nineteenth and early twentieth centuries. 1 The consequent emergence of sexuality as an object of study was one of the major features of the social sciences of the period, and stands as a central moment in the constitution of modern concepts. As Max Hodann, a German writer on sex and a former colleague of the great pioneer Magnus Hirschfeld, put it: ‘The focus of conflict and emotional tension for the nineteenth century was the Darwinian theory. In the twentieth, the stress has shifted to the scientific investigation and discussion of sexual matters.’ 2