The Road Not Taken: What Developmental Psychology Might Learn From Darwin's Insights Concerning Sexual Selection.

Developmental Psychology is the branch of psychology that studies, not only human behavior, but how and why human behavior changes over time. This essay seeks to review to what extent Developmental Psychology has failed to perceive human behavior through the lens of evolutionary theory in general, and in particular sexual selection as first described by Darwin and later elaborated on by many, including Robert Trivers and Geoffrey Miller; the essay asserts that this failure has resulted in many wrong turns and missed opportunities. In some cases, major developmental theorists (e.g., Freud, Erikson) were bedeviled by sex-based differences which they saw but could not explain and which compromised the parsimony of their stage theories. In the case of stage theories of moral development, some major theorists (e.g., Piaget, Kohlberg) were able to offer simpler explanations of moral development only by limiting their studies to male subjects. And, while Developmental Psychology textbooks thoroughly describe sex differences in the timing of morphological changes in puberty, writers seldom discuss why the timing is different in the two sexes, universally, and functionally. On the other hand, several domains of developmental focus, including play, mate choice, parenting, and spatial cognition, have seen successful research efforts that utilized sexually selected predispositions as foundational assumptions. The essay concludes with a discussion of how a more evolutionary and functional view of human behavior might move the field of Developmental Psychology to an even more robust and accurate understanding of how humans change over the course of a lifetime.

Sources of marital conflict in five cultures.

This analysis of previously collected data examined four fitness-relevant issues for their possible role in marital conflict. These were sex, finances, division of labor, and raising children, selected in light of their pertinence to sex differences in reproductive strategies. Over 2,000 couples in five diverse cultures were studied. Marital conflict was assessed by the Problems with Partner scale, which was previously shown to demonstrate measurement invariance across cultures and genders. All four issues were significantly related to perceived marital problems in almost all cases. Thus, conflict tended to arise around issues relevant to reproductive strategies. A few cultural idiosyncrasies emerged and are discussed. In all cultures, wives reported more problems than husbands. Another important issue was kindness. The results suggest that a key factor in marital success or failure may be kindness necessary to sustain this prolonged and intimate relationship of cooperation for raising one's offspring.

Social status moderates the relationship between facial structure and aggression.

A growing body of evidence has linked individual differences in facial structure-in particular, the facial width-to-height ratio (FWHR)-to social behaviors, including aggression, cheating, and nonreciprocation of trust. In the research reported here, we extended this work by demonstrating that the association between FWHR and aggression is moderated by subjective and objective measures of social status. In Study 1 (N = 237 college students), FWHR was positively correlated with aggressive behavior, but only among men reporting relatively low social status. In Study 2 (N = 891 professional hockey players), FWHR was positively correlated with penalty minutes, but only among players who earned relatively low salaries. Collectively, these studies provide compelling evidence for the role of social status in moderating the relationship between facial structure and aggression, indicating that FWHR is a robust predictor of aggressive behavior, but only in the context of relatively low social status.

Applying evolutionary thinking to the study of emotion.

This paper argues for invoking evolutionary, functional thinking in analyzing emotions. It suggests that the fitness needs of normal individuals be kept in mind when trying to understand emotional behavior. This point of view is elaborated in sections addressing these topics: defining emotion; applying comparative analysis to the study of emotions; focusing on the elicitors and resulting motivated behaviors mediated by the various affects; recognizing that not all emotions have prominent, distinct facial expressions; acknowledging all of the basic emotions and not just some exemplars; crediting the more sensible Cannon-Bard theory over James-Lange; recognizing the more ancient, fundamental role of the limbic system in emotion compared with that of the neocortex; and analyzing socio-emotional interactions as they occur naturally, not just individual emotional behavior studied under artificial conditions. Describing the various facets and neuroendocrine mechanisms of each basic emotion can provide a framework for understanding the normal and pathological development of each emotion. Such an inventory, or ethogram, would provide a comprehensive list of all of the observable behavioral tendencies of our species.

Dominance-popularity status, behavior, and the emergence of sexual activity in young adolescents.

In this paper, we investigated the sexual activity levels of several subtypes of middle adolescents (age 14-15 years). The subtype profiles were based on dominance-popularity status and a range of behaviors associated with dominance and popularity. In addition, gender differences in behavioral profiles were examined among dominant-popular, sexually active young adolescents. Results showed that socially dominant and popular young adolescent boys who exhibited a highly aggressive profile were more sexually active than their low-status and non-aggressive male peers; dominant-popular girls who were very attractive and gossips were more sexually active than their female peers. The results are discussed from an evolutionary psychological framework.

Sex differences and similarities in married couples: patterns across and within cultures.

In this study, we examined the patterns of sex differences in men and women married to each other in five cultures (China, Russia, Turkey, UK, and the U.S.) to look for universal patterns in behavioral dimorphisms and for cultural variability in those patterns. Over 400 couples in each cultural group completed the 235-item Marriage and Relationship Questionnaire on various aspects of marriage, appropriately translated for each culture. Sex differences were anticipated in responses related to female choosiness, labor performed, emotional expressiveness, interest in sex, physical attractiveness, and jealousy. To measure male-female differences in each culture, t-tests were utilized, and effect sizes were calculated. Significant sex differences (p < .05, two-tailed) emerged in all six areas examined, although cultural differences were also seen in the patterns. For example, on items relevant to female choosiness, women in most, but not all, cultures were more likely than their husbands to endorse these statements: "I have thought of divorcing my spouse" and "My parents played a role in choosing my spouse." In China, where scores on emotional expressiveness were low, sex differences disappeared in the category related to emotions. Results suggest that long-term marriage exhibits a balance between homogamy and dimorphism serving reproductive interests. Moreover, culture may moderate this balance for particular sex differences.

Sexual imprinting in human mate choice.

Animal and human studies have shown that individuals choose mates partly on the basis of similarity, a tendency referred to as homogamy. Several authors have suggested that a specific innate recognition mechanism, phenotypic matching, allows the organism to detect similar others by their resemblance to itself. However, several objections have been raised to this theory on both empirical and theoretical grounds. Here, we report that homogamy in humans is attained partly by sexual imprinting on the opposite-sex parent during childhood. We hypothesized that children fashion a mental model of their opposite-sex parent's phenotype that is used as a template for acquiring mates. To disentangle the effects of phenotypic matching and sexual imprinting, adopted daughters and their rearing families were examined. Judges found significant resemblance on facial traits between daughter's husband and her adoptive father. Furthermore, this effect may be modified by the quality of the father-daughter relationship during childhood. Daughters who received more emotional support from their adoptive father were more likely to choose mates similar to the father than those whose father provided a less positive emotional atmosphere.

Current evolutionary perspectives on adolescent romantic relations and sexuality.

This article describes current evolutionary research on adolescent sexual and romantic behavior. It first reviews functional explanations for basic sex differences in behavior. As in other pair-bonding mammals, women seek dominant males, and men seek and guard young, fertile females. Recent work is then described on adolescent competitiveness, mate selection, and pair bonding. The outcomes of even childhood social competition can be profound, with healthy, early-maturing, attractive children deriving lifelong benefits. Adolescent competition is intense among girls as well as boys. Depression is more common for boys with few sex partners, and for girls with many. Based on cross-cultural data and on analysis of pubertal changes in girls and boys, it can be concluded that adolescents have an evolved propensity for early sexual experimentation, followed by more judicious mate choice. Yet the bond with a girl's first sex partner is often profound. Amorous infatuations are intense in both sexes and usually mitigate within 3 years, for plausible adaptive reasons. Early menarche and unmarried motherhood impose developmental disadvantages on children but may be an evolved adaptation for stressful family conditions and a shortage of marriageable men. Gaining an understanding of normal adolescence can help in diagnosing, preventing, and treating problematic behaviors.

Possible olfaction-based mechanisms in human kin recognition and inbreeding avoidance.

Three studies explored kin recognition through olfaction. In Study I, adults (N=22) were tested for ability to identify the odors of themselves; their mother; their father; a sister; a brother; a familiar, unrelated individual; and a stranger. Acquaintances were identified as accurately as biological kin, implicating an association mechanism. However, biological kin were often confused, implicating phenotypic matching. Same-sex kin were confused more than opposite-sex kin, but mainly when same-sex kin had odors of similar intensity. Study II implicated phenotypic matching. Mothers (N=18) could identify their biological children but not their stepchildren. The preadolescent children (N=37) identified their full siblings but not half-siblings or stepsiblings. Thus, olfactory cues may help mediate favoritism of blood relatives. In Study III, mutual olfactory aversion occurred only in the father-daughter and brother-sister nuclear family relationships. Recognition occurred between opposite-sex siblings but not same-sex siblings. Thus, olfaction may help mediate the development of incest avoidance during childhood (the Westermarck effect).

Marriage: an evolutionary perspective.

Marriage is universal, and pair bonding is found in other species too with highly dependent young. So marriage functions as a reproductive social arrangement that traditionally involved the extended family. The sexes are not identical in their biological contributions to children's survival, so they seek somewhat different attributes in a mate. Men seek a young, attractive, sexually faithful bride. Women seek a man who is older, taller, and (as in many other species) socially dominant. Both sexes prefer a kind, healthy, attractive, similar mate who is emotionally attached to them. A spouse who fails to maintain sufficiently high mate value is vulnerable to divorce. Infertility and sexual dissatisfaction predict divorce, as does death of a child, but the more children, the stabler the marriage. Cross-cultural data suggest that cruel or subdominant men (e.g., poor providers) and unfaithful women are prone to divorce. Marriages in which the wife dominates the husband in economic contributions, nonverbal behavior, and decision making tend to be less satisfying. In societies in which wives are economically independent of husbands, divorce rates are high. As women's economic power has risen with industrialization, divorce rates have climbed. Economic and fitness considerations also help explain cultural differences in polygyny, age at marriage, arranged marriage, concern with the bride's sexual chastity, and marriage ceremonies. Other factors also affect marital dynamics, such as state subsidies to families, the sex ratio, and influence of the couple's parents.