Pluralistic evolutionary theories of human mating argue that Darwinian sexual selection favored strategies that offered flexibility in response to a wide range of contexts (Gangestad & Simpson, 2000; Belsky, 1999). This pluralistic approach suggests that people possess both long-term and short-term mating strategies (Buss & Schmitt, 1993; Lancaster, 1989).
This view proposes that men and women carry different design features of sexual desire that generate multiple forms of human mating. When men pursue short-term mates, for example, the underlying motivation appears to be the desire for sexual variety. When women pursue short-term partners, on the other hand, the driving force is not a passion for large numbers but seems based on securing males with genetic quality (Gangestad & Simpson, 2000).
Because short-term strategies for men and women appear to solve different adaptive problems, pluralistic approaches predict that men will report, on average, greater preference for sexual variety than women. A team of researchers directed by David Schmitt (2003) found cross-cultural empirical support for sex differences in the desire for sexual variety in a survey of 16,288 people across ten major world regions (including North America, South America, Western Europe, Eastern Europe, Southern Europe, the Middle East, Africa, Oceania, South/Southeast Asia, and East Asia).
Parental Investment Theory
The seminal logic of parental investment theory (Trivers, 1972) serves as the foundation for nearly all evolutionary theories of human mating. In many species (e.g., most mammals), females provide more parental investment—directing time and energy at offspring care—than do males. In some species, such as seahorses or pipefish, males provide the bulk of parental care (Wilson, Vincent, Ahnesjö, & Meyer, 2001; Mormon crickets: Gwynne, 1984).
The theory of parental investment argues that the relative proportion of parental investment varies across species because the onus of parental investment is tied to male-female differences in mating strategies. Specifically, within a species, the sex that invests more shows greater discrimination in selecting mates. The sex that invests less is willing to mate with more partners and with less courtship than the heavier investing sex (Andersson, 1994; Bateson, 1983; Clutton-Brock & Parker, 1992; Maynard Smith, 1977).
The psychological mechanisms that guide female decision-making about sexual partners were shaped in response to the costs associated with poor mate choices. Among humans, females across cultures are considerably more active in parenting than males, despite the fact that, compared to other mammals, human males invest heavily in offspring (Low, 1989).
Nowhere are sex differences in parental investment more visible than in the minimum commitment required to produce viable progeny (Symons, 1979). In a purely biological sense, women are obligated to pay the physical, emotional, and time-related costs associated with a long gestation period in order to reproduce. The only biological imperative for men, in contrast, is the contribution of sperm. In addition, women—but not men—have historically incurred the cost of lactation in the months that follow birth. During this time, it is more difficult for women to pursue mates, reproduce, and invest in additional offspring than it is for men.
When viewed through the lens of parental investment theory (Trivers, 1972), the differences in minimal parental investment should result in men (i.e., the lesser investing sex) displaying lower levels of choosiness in mate selection and greater intrasexual competitiveness (i.e., male-male competition). Accordingly, research has shown that men experience earlier death than women across cultures (Alexander & Noonan, 1979), delayed maturation (Geary, 1998), riskier life-history strategies (Daly & Wilson, 1988), and greater aggression and physical size (Archer & Lloyd, 2002). In the context of short term mating, females are almost always more discriminating with respect to partner preferences (Simpson & Gangestad, 1992; Buss & Schmitt, 1993).
In sum, there is considerable evidence that when men pursue short-term mates, they desire large numbers of sex partners and are generally quick to consent to sex, whereas when women pursue short-term mates, they appear motivated more by partner quality than by partner quantity. This research also suggests that pluralistic theories of human mating are more likely to be correct than competing alternatives in which all humans are equipped with a singular (either long-term or short-term) mating strategy.