Early psychosocial stress affects men's relationship length

Journal of Sex Research, July-August, 2009 by Nicole Koehler, James S. Chisholm

Short-term mating refers to a sexual relationship that takes place on a single occasion (e.g., a 1-night stand); over several days; or, at most, over a few weeks (Wiederman & Dubois, 1998). It does not refer to a steady boyfriend, girlfriend, or a potential spouse. Long-term mating refers to a relationship that takes place for more than a few months, possibly leading to a long-lasting relationship, such as marriage (Wiederman & Dubois, 1998). The aim of this study was to examine the effects early psychosocial stress (e.g., parental divorce, sexual abuse, etc.) has on relationship lengths from an evolutionary perspective. First however, we review the literature on gender differences with regards to relationship lengths. Then, we discuss evolutionary theory and evidence indicating that early psychosocial stress should affect relationship lengths.

Gender differences in preferences for short- and long-term mating have been widely reported and interpreted as reflecting the differing initial reproductive investments by men and women. Women have a higher initial cost of reproduction because of a long period of gestation followed by lactation than men, for whom the contribution of sperm comparatively costs them virtually nothing (Bribiescas, 2001; Clutton-Brock & Parker, 1992; Lancaster, 1997; Symons, 1979; Trivers, 1972; Williams, 1966, 1975). Even after weaning, when parental investment could potentially be provided equally by both parents, women usually still provide more parental investment than men (Trivers, 1972).

Given these initial reproductive investment differences, women are predicted to be choosier than men when it comes to selecting a short-term mate (Buss & Schmitt, 1993; Geary, Vigil, & Byrd-Craven, 2004; Kenrick, Groth, Trost, & Sadalla, 1993; Kenrick, Sadalla, Groth, & Trost, 1990; but, see also Hrdy, 2000; and Smuts, 1992, 1995, for evidence suggesting that females, especially among nonhuman primates, may lack mate choice because of male sexual coercion, which can involve infanticide and forced copulations). Because the potential costs of a short-term relationship (e.g., risk of contracting sexually transmitted diseases, risk of unwanted pregnancy, and decreased value as a long-term partner) usually outweigh the potential benefits (e.g., obtaining some resources from her mate and obtaining genetic benefits for her offspring), most women are thought to avoid this type of mating strategy (Geary et al., 2004). However, it is known that women may engage in short-term matings for the following reasons: (a) to obtain short-term material resources and even long-term resources in form of a woman's potential access through his kin (in some societies), (b) "good genes," (c) increase genetic diversity of offspring, (d) paternity confusion, (e) protection from other men, and (f) social-emotional security (Hrdy, 1981; Jennions & Petrie, 2000; Kempenaers, Congdon, Boag, & Robertson, 1999; Small, 1992; Smith, 1984; Yasui, 1998). For men, on the other hand, the benefits of short-term relationships (reproductive potential with no parental investment) usually outweigh the costs (risk of contracting sexually transmitted diseases and little or no investment), especially when not currently in a long-term relationship (Buss & Schmitt, 1993). Thus men are expected to be less choosy when it comes to selecting mates for short-term relationships than women, which has been demonstrated by findings showing that men are more likely to engage in casual sex (Buss & Schmitt, 1993; Chara & Kuennen, 1994; Clark, 1990; Clark & Hatfield, 1989; Oliver & Hyde, 1993; Surbey & Conohan, 2000) and that they desire more sexual partners (Buss & Schmitt, 1993; Darling & Davidson, 1986; Einon, 1994) than women.

Both genders are choosy when it comes to selecting mates for long-term relationships (Kenrick et al., 1993, 1990). In long-term relationships, women benefit by obtaining resources and paternal investment from their mates at the costs of restricted sexual opportunities and sexual obligations to their mates; men benefit from increased paternity certainty, higher quality children, and having a sexual and social companion at the costs of restricted sexual opportunities and heavy parental and relationship investment (Geary et al., 2004).

Everything else being equal then, given the differences in reproductive investments by men and women, men are generally expected to maximize fitness by pursuing short-term relationships with little or no paternal investment, whereas women are expected to maximize fitness by pursuing long-term relationships to obtain paternal investment for their offspring. Taken to the extreme, however, if all men rigorously pursued short-term matings only, and women rigorously pursued long-term matings only, then there would not be any matings at all, as the desired strategy of each gender would not match that desired by the opposite gender. Thus, there must be individual differences in within-gender mating strategies, as well as some individuals pursuing a mixed-mating strategy (Gangestad & Simpson, 2000). The individual difference of particular interest within this study is early psychosocial stress, which is discussed later.