Growing interest in sexual conflict since the late 1980s reflects several developments within behavioral ecology. These include recognition of females as active participants in co-evolutionary interactions, 1-3 demonstrations of high levels of extrapaternity in many ''monogamous'' species, 4 remarkable evidence of life-threatening toxic compounds in the sperm of fruit flies, 5 and experimental studies revealing deleterious consequences of arms races for both males and females. 6 Many of the ideas in this new body of work were sparked by Parker's papers on how sexual conflict shapes physiological and behavioral traits. These ideas were brought to popular attention by Dawkins, 7:140 who posed the question: ''If there is conflict of interests between parents and children, who share 50% of each others' genes, how much more severe must be the conflict between mates, who are not related to each other?'' Research into sexual conflict among nonhuman primates is flourishing, 8 but has received less explicit attention in the study of humans, despite cogent arguments that women's strategies are often constrained by the forceful and manipulative behavior of men and their kin.3,9 Here we explore new hypotheses for the extent and direction of sexual conflict among humans, both within and between populations, focusing on signaling mate quality, family size preferences, and the marital bond.''It is a long way to school here, all the way from Mahmudabad. Dangerous. An hour at least. A girl shouldn't go to school if it is so far away. It just shows.'' ''He followed them . . . he jumped out from behind a rock. . .'' ''She won't get a husband after this.'' ''. . .the judge told her she has to marry Abbas as soon as they catch him.'' ''They'll beat her up at home until she says yes . . .''.
10:113-118Parker's 11:124 definition of sexual conflict (Box 1) as ''a conflict between the evolutionary interests of individuals of the two sexes'' is both intuitive and all-encompassing. Sexual conflict occurs in two primary contexts: over mating, where males typically benefit more from mating with multiple partners than do females, 12 and over bi-parental care, where parents can increase their individual fitness by reducing their own efforts if there is compensation from the other parent. 13 Such conflicts lead to complex dynamic ''unresolvable evolutionary chases.'' These are classically portrayed through Parker's 14 extraordinary descriptions of female yellow Box 1. Glossary Sexual conflict -''A conflict between the evolutionary interests of individuals of the two sexes '' 11:124 ; sexual conflict occurs when the optimal value of a trait differs between the two sexes.Conflict (or shared) traitTraits that differ in value for the sexes because of sex-specific costs and benefits.Sexually antagonistic selection -Occurs when selective forces act on males and females in different directions.Sexually antagonistic coevolution -A chain of adaptations and counteradaptations during the struggle over sex-specific optimality in a given conflict tr...