Adaptive Individual Differences Revisited

Humans possess a complex array of evolved psychological mechanisms, only a subset of which is activated at any particular time. Attempts to reduce human sexual strategies to a single, rigid, invariant strategy, and to label departures from a single strategy as maladjusted, fail to accord with a large body of empirical evidence. Personality psychology cannot afford to ignore the rich repertoire of individual differences, some of which are adaptively patterned. The primary goal of our target article, “Adaptive Individual Differences,” was to offer a taxonomy of models of adaptive and nonadaptive individual differences (Buss & Greiling, this issue). We also provided conceptual standards and empirical procedures by which importantly different forms of individual differences could be distinguished. The goal was explicitly not to provide a detailed evaluation of the plausibility of the specific hypotheses about individual differences, but rather to outline the entire array for further scrutiny. In an eloquent and engaging commentary, Kirkpatrick (this issue) explores one of these conceptions in depth—the issue of whether individual differences in attachment styles and mating strategies represent adaptive individual differences (this falls under the heading of “early environmental calibration” in the target article) or, conversely, whether departures from secure attachment and long-term mating represent maladaptive deviations produced by evolutionarily novel environmental conditions. After reviewing the arguments and evidence, Kirkpatrick Journal of Personality 67:2, April 1999. Copyright © 1999 by Blackwell Publishers, 350 Main Street, Malden, MA 02148, USA, and 108 Cowley Road, Oxford, OX4 1JF, UK. Address all correspondence to: David M. Buss, Department of Psychology, University of Texas, Austin, TX 78712. E-mail: [email protected] concludes that indeed “humans possess both longand short-term strategies in their mating repertoires” (p. 253), precisely as outlined by Sexual Strategies Theory (Buss & Schmitt, 1993). The evidence Kirkpatrick marshals to support this conclusion are several: (1) there are adaptive advantages to short-term nonmonogamous mating under certain conditions; (2) these benefits are sex differentiated, such that men’s short-term mating will represent a larger component of the strategic repertoire than women’s; (3) men’s testes size relative to body weight suggests a human evolutionary history marked by some degree of multiple-partner mating; (4) sexual dimorphism for size and stature suggests a human evolutionary history of some polygyny; and (5) evidence on sexual jealousy and mate-guarding suggests a long evolutionary history in which the nonmonogamy of a partner was a recurrent adaptive problem (e.g., Buss & Shackelford, 1997). These data are compelling in support of Kirkpatrick’s conclusion, but there are other sources of evidence that also support Sexual Strategies Theory. These include: (6) behavioral data on the cross-cultural pervasiveness of extramarital affairs (Buss, 1994); (7) evidence on the nature of sexual fantasies (Ellis & Symons, 1990); (8) behavioral evidence on men’s willingness to have casual sex with attractive strangers (Clark & Hatfield, 1989); (9) physiological evidence on sperm insemination and retention (Baker & Bellis, 1995); (10) physiological evidence on the existence of sperm morphs designed to solve the adaptive problem of alien insemination (Baker & Bellis, 1995); (11) expressed desires for a number of sex partners (Buss & Schmitt, 1993); and (12) the fact that attitudes toward casual sex show large sex differences in meta-analyses of sex differences in sexuality (Oliver & Hyde, 1993). Given this voluminous evidence from so many different sources, it would seem that the burden of empirical proof must shift to those who continue to insist that humans have but a single, monolithic, uniform, long-term sexual strategy (see Buss, 1998, for a more extensive review of the evidence). Distinguishing Adaptive from Maladaptive Individual Differences At a more general level, Kirkpatrick’s commentary raises the issue of conceptual and evidentiary standards for distinguishing adaptive from maladaptive individual differences (Buss, Haselton, Shackelford, Bleske, & Wakefield, 1998). He argues that the high incidence of 260 Buss