. "8. Sexually Antagonistic Coevolution: Theory, Evidence, and Implications for Patterns of Human Mating and Fertility." Offspring: Human Fertility Behavior in Biodemographic Perspective. Washington, DC: The National Academies Press, 2003.
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Offspring: Human Fertility Behavior in Biodemographic Perspective
have created these circumstances in laboratory populations. In nearly all natural populations, however, this circumstance rarely if ever exists. Instead, although an ordering of events in terms of the extent to which they would promote or diminish the lifetime reproductive success of an individual may substantially covary with an ordering of events in terms of the extent to which they would promote or diminish the lifetime reproductive success of an individual’s mate, there is rarely perfect covariation. Mismatches in these orderings represent genetic conflicts of interest between the sexes within mateships. These genetic conflicts of interest can produce selection for characteristics of members of one sex that promote the fitness of that sex at the expense of the fitness of the other. The outcome of such selection is referred to as sexually antagonistic adaptation (Rice, 1996). Although sexual conflicts of interest have long been recognized in evolutionary biology, only in the past several years have evolutionary biologists come to appreciate the dramatic ways by which the selection they fuel can influence the dynamics of mating, affect patterns of fertility, and explain outcomes that otherwise appear inexplicable.
This chapter paper has several aims. First, I discuss experimental work on the effects of sexual conflicts of interest in laboratory and field populations. Second, I summarize, at a conceptual level, the main consequences of selection fueled by sexual conflicts of interest. Third, I provide an overview of work suggesting that sexual conflicts of interest may have been common in ancestral human populations and hence had opportunity to affect selection on human mating and reproduction. Fourth, I describe three examples of how sexual conflicts of interest have affected specific phenotypic characteristics and mechanisms that, in turn, affect patterns of fertility. Finally, I will discuss the important ways by which sexual conflicts may have varied ancestrally in systematic ways, such that the outcomes of selection fueled by them may be expressed contingently, depending on particular circumstances.
EXPERIMENTAL DEMONSTRATIONS OF SEXUAL CONFLICTS OF INTEREST
Evolving Male Lines, with No Selection Mediated by Female Success
In 1996, William Rice published a spectacular demonstration of sexually antagonistic adaptation fueled by sexual conflicts of interest. Though an ingenious procedure, he allowed Drosophila melanogaster males to evolve while preventing females from evolving counteradaptations. Females in the line were always taken from a nonresponding target stock, whereas males were taken from the adapting-male line. Furthermore, artificial selection procedures ensured that males in the line always passed on the genes