Strategies of Human Mating

Modern humans have inherited the mating strategies that led to the success of their ancestors. These strategies include long-term mating, short-term mating, extra-pair mating, mate poaching, and mate guarding. This article presents empirical evidence supporting evolution-based hypotheses about the complexities of these mating strategies. Since men and women historically confronted different adaptive problems in the mating domain, the sexes differ profoundly in evolved strategic solutions. These differences include possessing different mate preferences, different desires for short-term mating, and differences in the triggers that evoke sexual jealousy. The study of human mating is one of the “success stories” of evolutionary psychology. Strategies of Human Mating No adaptive domain is more central to reproduction than mating. Those in our evolutionary past who failed to mate failed to become ancestors. Modern humans are all descendants of a long and unbroken line of ancestors who succeeded in the complex tasks involved required to mate successfully. As their descendants, modern humans have inherited the adaptations that led to the success of their ancestors. Successful mating requires solutions of a number of difficult adaptive problems. These including selecting a fertile mate, out-competing same-sex rivals in attracting a mate, fending off mate poachers (those who try to lure one’s mate away), preventing the mate from leaving, and engaging in all of the necessarily sexual and social behaviors required for successful conception to take place. As a consequence of the number and complexity of mating problems humans have recurrently faced over the long expanse of human evolutionary history, it is PSYCHOLOGICAL TOPICS 15 (2006), 2, 239-260 240 reasonable to anticipate that humans have evolved a large and complex array of adaptations specifically dedicated to the task of mating. Nowhere do people have an equal desire to mate with all people. Everywhere, some people are preferred as mates, others shunned. Desires are central to all facets of mating. They determine who we are attracted to, and who is attracted to us. They influence which attraction tactics will be successful (those that fulfill desires) and which attraction tactics will fail (those that violate desires). Successful mate retention tactics involve continuing to provide resources that fulfill the desires of a mate. Failure to fulfill these desires causes breakup and divorce. At every step of the mating process, from mate selection to mate expulsion, desires determine the ground rules. Sexual Selection and Parental Investment Although Charles Darwin (1859) recognized that survival was central to the evolutionary process, many natural phenomena he observed seemed to baffling on the theory of “survival selection.” He noticed phenomena such as the brilliant plumage of peacocks, the flamboyant feathers of cardinals, and the enormous antlers of deer. How could these metabolically costly features possibly have evolved? Many seemed like open lures to predators, and hence detrimental to survival. Darwin also noticed that males and females of many species appeared to be different in size and shape. Male elephant seals, for example, weight roughly 4,000 pounds; female elephant seals weigh only 1,000 pounds. Among baboons, males are twice the size of females. Among humans, males are 12 percent taller than females, on average. Since both sexes have faced roughly the same survival problems, why would they differ in size and morphology? And what could account for variation on the degree of sexual dimorphism across species? Darwin’s answer to these empirical puzzles was the theory of sexual selection (Darwin, 1858, 1871). The theory of sexual selection dealt with the evolution of characteristics due to mating, rather than survival, advantage. Darwin described two component processes through which sexual selection could take place. In the first, called intrasexual competition, members of one sex (often, but not always, the males) engaged in competitive battles with each other. Two stags locking horns in combat is an excellent example of intrasexual competition. The victors in these battles gain preferential sexual access to females. The losers fail to mate. The qualities that lead to success in same-sex contests, therefore, are passed down in greater numbers (assuming that these qualities are partly heritable). Whatever qualities are linked with losing either fail to get passed down. Evolution, that is change over time, occurs as a result of the differential reproduction of the winners and losers in same-sex contests. It is important to note that intrasexual competition need not always direct physical combat. Males in some species compete for position in the status or PSYCHOLOGICAL TOPICS 15 (2006), 2, 239-260 241 dominance hierarchy through non-physical means, and position in the hierarchy can be linked with preferential access to mates (e.g., Betzig, 1986; Buss, 1994/2003). Males in other species scramble for access to territory, and access to territory can be linked to preferential access to mates. The key point is that whatever qualities lead to success in intrasexual competition are passed on in greater numbers, whether the competition is physical combat, maneuvering for position in the hierarchy, or scramble for access to certain resources. The result is evolution through sexual selection. The second process through which sexual selection occurs is intersexual selection. This process involves the preferences of members of one sex for members of the opposite sex who possess certain qualities. Hypothetically, if all women preferred to mate with men who had red hair, those with red hair would have a mating advantage. Over time, we would witness an increase in the frequency of red-headedness in the population. The key point is that the desires of one sex for certain qualities in a mate can create evolutionary change either an increase in the frequency of desired qualities or a decrease in the frequency of undesired qualities. Although Darwin called this process “female choice,” it is clear that in many species, and certainly in humans, males also exert considerable mate choice. Theoretically, the mate preferences of one sex can determine over evolutionary time the domains in which the opposite sex competes (see Figure 1). If females desire males who build sturdy nests, then males will compete with each other to construct nests that embody the female preferences. Conversely, the domains in which one sex competes can influence the evolution of mate preferences in the other sex. If males compete with other males to monopolize resource-rich territories, for example, females might subsequently evolve a mate preference for males with large territories. Thus, mate preferences and patterns of intrasexual competition can co-evolve, each influencing the other. Figure 1. Sexual Selection Subsumes the Processes of Intrasexual Competition and Intersexual Selection