"A principal speculation of the medical experts in this era was that the masculine “will” or “instinct” to reproduce had been somehow affected by the spread of degeneracy. As the “active” agent in reproduction, men were assumed, both in biological science and in popular culture, to be the efficient cause of lowered natality. The contemporary campaigns against wet-nursing and infanticide are clear testimony that women were held responsible in some measure for the depopulation problem, but most of the responsibility fell on males. While women might be “sterile” (though this possibility was badly understood until after 1914), their “impotence" (frigidity) was only a partial barrier to pregnancy. Male sterility was better understood and documented, but male impotence was generally assumed to be the major cause of childless marriages, and had been so regarded since the old regime.
The nineteenth-century understanding of male impotence was linked to a venerable principle in French (and European) physiology, which held that sexual function, like all other bodily activities, was dependent on the maintenance of an equilibrium of vital forces, a sort of biological “golden mean” among the various functions of the organism (nutritive, reproductive, etc). According to this concept, the overall “animal economy” could be depleted by an excessive expenditure within any of these autonomous systems. Indeed, the experimental criterion for deciding on the biological norms of the normal and the pathological was the rate of energy expenditure. Moderate (average) rates of expenditure were deemed normal, and excessive or insufficient rates were judged to fall in the range of the pathological.
With respect to the sexual function-and this precept held equally for women—excessive sexual activity exhausted the organism, destroying the dynamism characteristic of sexual function and leading to impotence or, in more severe cases, to sterility. As the “genital” instincts, as they were called, drained from the organic structures that housed them (the genitals), it was believed that the organs themselves were altered, together with all the secondary sexual characters of the individual. This process produced anatomical abnormalities that doctors believed to be the stigmata of degeneration. Though excessive copulation could bring about this result, medical specialists from the late eighteenth century on believed that the most likely explanation was masturbation. Both activities, by making pleasure rather than reproduction the end of sexual activity, disrupted the “normal” and intrinsic aim of the genital instincts and led directly to exhaustion and premature death.
Most medical specialists in the early nineteenth century, in keeping with the principle of the old humoral medicine that men embodied the qualities of heat and dryness and women those of coolness and moistness, believed that men “spent” far more in the sex act than did women. Men were therefore especially prone to exhaustion and functional impotence. This basic distinction between the sexes was maintained throughout the nineteenth century, assuming the form of evolutionary discourse after 1870 or so. The evolutionary explanation for the differences between men and women was that a woman was more biologically primitive than a man, a case of arrested embryological development.
Women were therefore more “instinctive” (read “natural”) than men; women’s animal economies functioned more smoothly than those of men because less of their vital energy was directed away from the organism and toward the cerebrally based function of higher reason. Engaged as they were in the world of affairs, so the argument went, men had a far greater opportunity to exhaust themselves in overwork, where their superior capacity to reason was an ironic liability in the struggle for survival. Males’ “genital instincts” (“sexual instincts” after 1880 or so) were therefore less reliable, less certain in aim and duration than those of women, despite the apparently greater short-run violence of their sexual behavior."
—Robert A. Nye