Significant advances in understanding human sexuality have been made by examining behavioral patterns and associated feelings through an evolutionary perspective. Theory and research in the related fields of behavioral ecology, evolutionary anthropology, and evolutionary psychology suggest that men and women have evolved to think and behave differently with regard to sexual relationships. Although environmental conditions and cultural milieu can make male and female behaviors converge, the underlying tendencies of the two sexes differ and rest on fundamental differences in the evolved psychology of being male and being female (e.g., Buss, 1994; Cronk, 1991; Smith & Winterhalder, 1992; Wright, 1994). A variety of approaches and evidence have been used in the literature to assess predictions derived from this perspective, including data from closed-ended survey questionnaires, cross-cultural secondary analysis of ethnographic descriptions, and data derived though experimental psychology studies. Each approach has strengths and weaknesses, but all share the same theoretical base.
Scholars involved in these emerging fields have made little use so far of the recent substantial accumulation of qualitative data on sexual behavior and attitudes that have been generated from research stimulated by concerns about the international HIV/AIDS epidemic. Such data are increasingly available in both the developed and less developed countries around the world. The cultural diversity an complexity across societies call for more in-depth, open-ended types of information on these issues than can be elicited through survey questions. Thus, qualitative approaches are now being advocated and tried (Caldwell, 1993; Kitzinger, 1994; Pickering, 1988; Scrimshaw, Carballo, Ramos, & Blair, 1991; Smith, 1993; Standing, 1992).
We analyzed data on sexual attitudes and behavior of married men and women in Thailand derived through both focus group and individual interview techniques; the project was originally designed to study the influence of wives and male peers on married Thai males' attitudes and behavior with respect to extramarital sex. Unlike survey questionnaires, these qualitative research techniques allow the researcher to elaborate on the questions being asked and encourage study informants to explain their answers, with all the detail being recorded and available for analysis. Moreover, the conversational nature of the approaches fosters rapport, which is crucial when dealing with potentially sensitive sexual matters.
Although in the original project we did not anticipate that the results would be used to explore themes derived from evolutionary theory, a surprising amount of relevant data was generated for this purpose. Our primary goal in the current analysis was to interpret these data in light of hypotheses about male and female sexuality that have emerged from the evolutionary perspective. A secondary goal was to illustrate how, qualitative data derived from focus group discussions and focused in-depth interviews can be a rich complement to the more typical quantitative data used to test hypotheses generated through an evolutionary perspective.
We hope this approach will deepen understanding of Thai sexual patterns; at the same time, our analysis provides an interesting testing ground for the perspective. Thai society and culture are far removed from the West, from which the originators of the perspective come and most testing of the predictions has been based. One notable feature in which Thai sexual practices differ substantially from those prevalent in the West is in the high availability of commercial sex services and the relative social tolerance of their patronage (Boonchalaksi & Guest, 1994). For example, in a recent study of unmarried military recruits, with an average age of 22, 87% reported having had sex with a prostitute at some time (VanLandingham, Suprasert, Sittitrai, Vaddhanaphuti, & Grandjean, 1993). According to the 1990 urban survey by the Deemar Company (1990), 27% of single men (age 15 and older) and 9% of married men reported sex with a prostitute in the prior 12 months. Higher levels were found in a 1991 national survey: 40% of urban and 38% of rural never-married men reported sex with a commercial sex partner during the last 12 months, and 22% of urban and 9% of rural married men living with a spouse reported having commercial sex during the prior year (Sittitrai, Phanuphak, Barry, & Brown, 1992). This feature of the Thai setting adds to the interest of interpreting sexual attitudes and behavior within the framework of evolutionary psychology hypotheses.
The Evolutionary roach to Sexual Behavior and Attitudes
All living organisms have evolved through processes of natural and sexual selection that favor behaviors and traits that are most likely to leave a genetic legacy. These in turn operate through mechanisms such as striving for matings, investing in offspring, or helping other genetic relatives. There is growing evidence that humans are not immune from this principle; to survive and persist, humans must solve the same adaptive problems as all other species. Evolutionists argue that people have evolved to behave in ways that do, or did, contribute to their reproductive success (e.g., Alexander & Tinkle, 1981; Boyd & Richerson, 1985; Chagnon & Irons, 1979; Daly & Wilson, 1983; Durham, 1991; Lumsden & Wilson, 1981).
Evolutionarily, in most species and under most conditions, individuals who specialize in either mating (i.e., seeking sexual partners) or parental effort (i.e., caring for offspring) tend to leave more descendents. In part, this is because the behaviors that make one successful in mating are often mutually exclusive of the behaviors that promote parental success (reviewed by Low, 1993; also Daly & Wilson, 1983). For example, searching or fighting for a mate may involve risk taking, which is antithetical to surviving to nurse a dependent offspring. Thus, the reproductive "return curves" (reproductive success per unit of effort expended and risks taken) differ for mating and parental effort. Mating effort is not only typically risky but has a high fixed cost that must be paid before any reproductive return is possible (getting established, gaining status); parental effort, in contrast, has a per capita cost that must be expended for each offspring. As a result, if one sex (males in most species) specializes in getting mates, and the other (usually females) in investing in offspring, the two sexes will behave very differently (e.g., Diamond, 1992; Low, 1993).
Despite all cultural variation, this underlying difference sets the scene for widespread, predictable sex differences among humans in what they seek in a mate and what they think about sexual matters. Women have typically lost more investment than men if they failed to rear a child successfully, for they provide the bulk of energetic investment during pregnancy and lactation. However, in most societies, from hunter-gatherers to modern industrial nations, children survive and enter society more successfully when their mothers are assisted by an investing spouse. Thus, women who were indifferent to a man's ability and willingness to contribute parental investment suffered in most evolutionary environments. As a result, whenever conditions are such that men can and do invest significantly, women should have evolved to be less interested in short-term pairings; more interested in attracting a wealthy, willing-to-invest mate for the long term; and more risk averse than men. Women's attitudes about men's infidelity are likely to be shaped by the cost to themselves and their children. We expect women to be less tolerant of their mate's long-term relationships with other women if they might divert resources to those women and those women's children and to be more tolerant of their spouse's short-term encounters, which involve little commitment on the part of either partner (e.g., Betzig, 1986).
Men, in contrast, have likely always profited from a dual strategy. On the one hand, like other male mammals, a mating itself takes little effort for a man, and when low-cost, temporary (free of subsequent commitment) liaisons are available, men are likely to be little concerned with the subtleties of child health and survival. In evolutionary history, men have been able to profit from short-term trysts (especially when women have been able to raise children successfully alone) far more than women; men also have lost less than women in time and effort when children died. Because resources are central to children's success in most societies, as men accumulate the resources that make marriage and successful rearing of well-invested, highly competitive legitimate children possible, they will seek wives. Thus, we expect men to be interested in both long-term and short-term relations, with somewhat different preferences in the women they seek for the two types of partnerships (e.g., Buss, 1994; Buss & Schmitt, 1993).
In the context of long-term mating, in which men provide significant paternal investment, they are predicted to be intolerant of any infidelity (short or long term) on the part of their wives, because it places the paternity of the offspring in question and thus produces a risk of investing in the children of another man (e.g., Buss, 1987, 1989, 1994; Cronk, 1991; Low, 1993). Mate-guarding tactics, i.e., practices that prevent their mate from having sexual contact with other males and thereby ensuring their confidence of paternity, should be common (see Buss, 1994; Buss & Schmitt, 1993).
Conscious or logical thought is not required for men and women to behave in typically reproductively profitable ways; rather, this is apparently accomplished through evolved psychological mechanisms (e.g., Buss, 1994; Cosmides & Tooby, …