Todd K. Shackelford

Adaptations, Exaptations, and Spandrels

Adaptation and natural selection are central concepts in the emerging science of evolutionary psychology. Natural selection is the only known causal process capable of producing complex functional organic mechanisms. These adaptations, along with their incidental by-products and a residue of noise, comprise all forms of life. Recently, S. J. Gould (1991) proposed that exaptations and spandrels may be more important than adaptations for evolutionary psychology. These refer to features that did not originally arise for their current use but rather were co-opted for new purposes. He suggested that many important phenomena--such as art, language, commerce, and war--although evolutionary in origin, are incidental spandrels of the large human brain. The authors outline the conceptual and evidentiary standards that apply to adaptations, exaptations, and spandrels and discuss the relative utility of these concepts for psychological science.

The Attractive Female Body Weight and Female Body Dissatisfaction in 26 Countries Across 10 World Regions: Results of the International Body Project I

This study reports results from the first International Body Project (IBP-I), which surveyed 7,434 individuals in 10 major world regions about body weight ideals and body dissatisfaction. Participants completed the female Contour Drawing Figure Rating Scale (CDFRS) and self-reported their exposure to Western and local media. Results indicated there were significant cross-regional differences in the ideal female figure and body dissatisfaction, but effect sizes were small across high-socioeconomic-status (SES) sites. Within cultures, heavier bodies were preferred in low-SES sites compared to high-SES sites in Malaysia and South Africa (ds = 1.94-2.49) but not in Austria. Participant age, body mass index (BMI), and Western media exposure predicted body weight ideals. BMI and Western media exposure predicted body dissatisfaction among women. Our results show that body dissatisfaction and desire for thinness is commonplace in high-SES settings across world regions, highlighting the need for international attention to this problem.

Human aggression in evolutionary psychological perspective

This article proposes an evolutionary psychological account of human aggression. The psychological mechanisms underlying aggression are hypothesized to be context-sensitive solutions to particular adaptive problems of social living. Seven adaptive problems are proposed for which aggression might have evolved as a solution--co-opting the resources of others, defending against attack, inflicting costs on same-sex rivals, negotiating status and power hierarchies, deterring rivals from future aggression, deterring mates from sexual infidelity, and reducing resources expended on genetically unrelated children. We outline several of the contexts in which humans confront these adaptive problems and the evolutionary logic of why men are cross-culturally more violently aggressive than women in particular contexts. The article concludes with a limited review of the empirical evidence surrounding each of the seven hypothesized functions of aggression and discusses the status and limitations of the current evolutionary psychological account.

Attractive Women Want it All: Good Genes, Economic Investment, Parenting Proclivities, and Emotional Commitment

The current research tests the hypothesis that women have an evolved mate value calibration adaptation that functions to raise or lower their standards in a long-term mate according to their own mate value. A womans physical attractiveness is a cardinal component of womens mate value. We correlated observer-assessed physical attractiveness (face, body, and overall) with expressed preferences for four clusters of mate characteristics (N = 214): (1) hypothesized good-gene indicators (e.g., masculinity, sexiness); (2) hypothesized good investment indicators (e.g., potential income); (3) good parenting indicators (e.g., desire for home and children), and (4) good partner indicators (e.g., being a loving partner). Results supported the hypothesis that high mate value women, as indexed by observer-judged physical attractiveness, expressed elevated standards for all four clusters of mate characteristics. Discussion focuses on potential design features of the hypothesized mate-value calibration adaptation, and suggests an important modification of the trade-off model of womens mating. A minority of women—notably those low in mate value who are able to escape male mate guarding and the manifold costs of an exposed infidelity—will pursue a mixed mating strategy, obtaining investment from one man and good genes from an extra-pair copulation partner (as the trade-off model predicts). Since the vast majority of women secure genes and direct benefits from the same man, however, most women will attempt to secure the best combination of all desired qualities from the same man.

FACIAL ATTRACTIVENESS AND PHYSICAL HEALTH

Abstract Previous research has documented that more facially attractive people are perceived by others to be physically healthier. Using self-reports, observer ratings, daily diary methodology, and psychophysiological assessments, this study provides limited empirical evidence that more facially attractive people ( N = 100) may be physically healthier than unattractive people. Discussion suggests the value of an evolutionary psychological perspective for understanding the relationship between facial attractiveness and physical health.

Emotional reactions to infidelity

We sought to identify emotional reactions to a partners sexual infidelity and emotional infidelity. In a preliminary study, 53 participants nominated emotional reactions to a partners sexual and emotional infidelity. In a second study, 655 participants rated each emotion for how likely it was to occur following sexual and emotional infidelity. Principal components analysis revealed 15 emotion components, including Hostile/Vengeful, Depressed, and Sexually aroused. We conducted repeated measures analyses of variance on the 15 components, with participant sex as the between-subjects factor and infidelity type as the within-subjects factor. A main effect for sex obtained for 9 components. For example, men scored higher on Homicidal/Suicidal, whereas women scored higher on Undesirable/Insecure. A main effect for infidelity type obtained for 12 components. For example, participants endorsed Nauseated/Repulsed as more likely to follow sexual infidelity and Undesirable/Insecure as more likely to follow emotional infidelity. Discussion addresses limitations of this research, and highlights the need for an integrative theory of emotional reactions to infidelity.

Reasoning about dead agents reveals possible adaptive trends

We investigated whether (a) people positively reevaluate the characters of recently dead others and (b) supernatural primes concerning an ambient dead agent serve to curb selfish intentions. In Study 1, participants made trait attributions to three strangers depicted in photographs; one week later, they returned to do the same but were informed that one of the strangers had died over the weekend. Participants rated the decedent target more favorably after learning of his death whereas ratings for the control targets remained unchanged between sessions. This effect was especially pronounced for traits dealing with the decedent’s prosocial tendencies (e.g., ethical, kind). In Study 2, a content analysis of obituaries revealed a similar emphasis on decedents’ prosocial attributes over other personality dimensions (e.g., achievement-relatedness, social skills). Finally, in Study 3, participants who were told of an alleged ghost in the laboratory were less likely to cheat on a competitive task than those who did not receive this supernatural prime. The findings are interpreted as evidence suggestive of adaptive design.

Forgiveness or breakup: Sex differences in responses to a partner's infidelity

Infidelities--sexual, emotional, or both--afflict many long-term romantic relationships. When a person discovers a partners betrayal, a major decision faced is to forgive the partner and remain together or to terminate the relationship. Because men and women have confronted different adaptive problems over evolutionary history associated with different forms of infidelity, we hypothesised the existence of sex differences in which aspects of infidelity would affect the likelihood of forgiveness or breakup. We tested this hypothesis using forced-choice dilemmas in which participants (N = 256) indicated how difficult it would be to forgive the partner and how likely they would be to break up with the partner, depending on the nature of the infidelity. Results support the hypothesis that men, relative to women: (a) find it more difficult to forgive a sexual infidelity than an emotional infidelity; and (b) are more likely to terminate a current relationship following a partners sexual infidelity than an emotional infidelity. The Discussion provides directions for future work on the determinants of breakup and the psychology of forgiveness.

Cues to Infidelity

This research sought to identify cues to a long-term partners sexual infidelity and emotional infidelity. In Study 1, 204 participants nominated acts that evoke suspicions of sexual or emotional infidelity. In Study 2, 230 participants evaluated these acts on how diagnostic each was of sexual and emotional infidelity. Factor analysis revealed 14 factors of cues, including Anger and Argumentativeness, Exaggerated Affection, Sexual Boredom, and Relationship Dissatisfaction. Twelve factors were differentially diagnostic of sexual versus emotional infidelity. Sexual Boredom, for example, was more diagnostic of sexual infidelity, whereas Relationship Dissatisfaction was more diagnostic of emotional infidelity. Men and women provided higher diagnosticity ratings for acts performed by an opposite-sex versus same-sex target. For ratings collapsed across sex of target, however, women provided higher diagnosticity ratings than did men. Discussion integrates results with previous research on infidelity and suggests important directions for future research on the cues to infidelity.

Betrayal in Mateships, Friendships, and Coalitions

Over evolutionary history, different benefits have been gained and lost from long-term mateships, friendships, and coalitions. Humans have evolved psychological mechanisms that are sensitive to cues to possible diversion of benefits to people outside the relationship. Mateships, friendships, and coalitions are predicted to share some of the same benefits but also to differ in some of the resources conferred. Accordingly, the psychological mechanisms sensitive to betrayal are predicted to operate in the same manner in those domains in which benefits are common across relationships and to operate differently in those domains in which benefits are unique to relationship type. Three interpersonal domains are investigated with regard to perceived betrayal: extra relationship intimate involvement, intrarelationship reciprocity, and relationship commitment. Eight hypotheses are tested across the three relationship domains via perceived betrayal judgments. Results support a model of betrayal entailing some degree of domain specificity but also some generality across domains.