Sex and Reason.

In this ambitious book, Judge Richard Posner presents an economic theory of sexuality that attempts to explain both the practice of sex and its regulation. Given the pressure on our legal system to address sexual issues raised by the AIDS epidemic, homosexual rights, sexual harassment in the workplace

Posner's approach is to conduct his analysis of sex as though it were a morally neutral subject. For example, the public regulation of food or traffic safety, unlike sexual activity, are issues of public concern but are not subjects normally "charged with moral significance." Its economic impact can be examined with scientific detachment. The author proposes to examine sexual activity and its regulation by applying the same economic model of rational behavior typically reserved for more traditional market and non-market activities. Some may wonder how sex can be viewed as rational. While the sex drive itself is viewed as a biological factor that is given, the decision to engage in particular sex acts are thought to be a matter of rational choice where individuals respond to incentives.

This book has two major themes. First, that variation in sexual practice across societies and over time can be explained by a small number of variables. The primary variables are urbanization, income, the sex ratio (the ratio of males to available females), scientific advances in the control of fertility, and above all, the changing occupational role of women. Posner uses these variables to explain society's behavior and attitudes about subjects as diverse as abortion, illegitimacy, homosexual behavior, prostitution, polygamy, infanticide, rape and pornography.

A key factor in Posner's analysis in explaining the evolution of sexual morality from ancient Greece to the modern era, along with the changing occupational role of women, is the trend to companionate marriage. This dominate form of marriage in the west today can be explained as one in which,

. . . the husband and wife are best friends, social and emotional intimates, close companions. The older form of marriage, noncompanionate marriage, is marriage in which the husband provides the wife with occasional insemination and financial support in exchange for her pledge of sexual fidelity, but there is no expectation of an intimate bond.