Very Preliminary Draft Comments Welcome THE EVOLUTIONARY BIOLOGY AND ECONOMICS OF SEXUAL BEHAVIOR AND INFIDELITY

Why might spouses cheat on one another? How might demographic or economic variables be implicated in sexual behavior and marital infidelity? Do patterns of infidelity differ depending on whether the cheating spouse in question is the husband or wife? How much might cheating matter for the economics of marriage and divorce? Answers to these questions are highly pertinent to our understanding of the economics of the family. For instance, divorce is associated with economic calamity—especially mothers and children—and a leading correlate of divorce is sexual infidelity. Despite the potential importance (and, as it turns out, prevalence) of infidelity, it is seldom addressed in the economics of the family. In contrast, cheating occupies a central role in biological models of mating behavior. I blend insights from biology and economics to generate hypotheses concerning the propensity to commit infidelity. Central to the biology-based approach is the idea that spouses behave as if reproductive concerns drive sexual behavior, and that the marked differences in female versus male reproductive biology imply corresponding differences in the incentives, concerns and interests of male versus female spouses. I investigate these hypotheses using the National Health and Social Life Survey (NHSLS), and find marked differences between husbands and wives, cohabiting partners and singles with respect to both attitudes and behavior regarding sexual activity and infidelity. These patterns are consistent with a “bio-founded” economic model of the family that gives a prominent role to the exigencies of reproductive biology. Such findings suggest significant potential of biological thinking for sharpening predictions of economic models of search, matching, mating, marriage and divorce. Such models seldom consider the possibility of cheating, but they should.