This study investigated sex differences in interest in infants among children, adolescents, young adults, and older individuals. Interest in infants was assessed with responses to images depicting animal and human infants versus adults, and with verbal responses to questionnaires. Clear sex differences, irrespective of age, emerged in all visual and verbal tests, with females being more interested in infants than males. Male interest in infants remained fairly stable across the four age groups, whereas female interest in infants was highest in (...) childhood and adolescence and declined thereafter, particularly for the responses to visual stimuli. The observed developmental changes in female interest in infants are consistent with the hypothesis that they represent a biological adaptation for parenting. (shrink)

Most putative cases of teaching in nonhuman animals involve parent-offspring interactions. The interpretation of these cases, particularly with regard to the cognitive processes involved, is controversial. Qualitative and quantitative observations made in nonhuman primates suggest that, in some species, mothers encourage their infants’ independent locomotion and that encouragement can be considered a form of instruction. In macaques, experience in raising previous offspring accounts in part for variability between mothers in propensity to encourage infant motor skills. Parsimony suggests that the cognitive (...) mechanisms underlying maternal encouragement of infant locomotion in primates as well as some other putative cases of animal teaching may involve first-order intentionality (i.e., goal-directed behavior) and not higher cognitive processes such as attribution of knowledge/ignorance or perspective-taking. Encouragement of infant independent locomotion early in life may have benefits to mothers later on, in terms of reduction of costs of infant carrying, earlier infant weaning, and increased probability of reproduction in the mating season. The elementary forms of teaching observed in nonhuman primates may have played an important role in the origin and evolution of human culture. (shrink)

Sex differences in aggressive behavior are probably adaptive but the costs and benefits of risky aggression to women and men may be different from those suggested in Campbell's target article. Moreover, sex differences are more likely to reflect differences in the costs of aggression to females and males rather than differences in its benefits.

Colic may allow infants to obtain additional investment from their parents. The lack of clear fitness costs of colic and of differences in condition between colicky and non-colicky infants is inconsistent with the hypotheses that colic is an honest signal of need or vigor. These and other characteristics of colic, however, are consistent with the hypothesis that colic is a manipulative signal.

In our response, we review and address the comments on our target article made in the 25 commentaries. First, we review and discuss the commentaries that recognized the value of our approach, accepted the main premises and conclusions of our target article, and suggested further avenues for research on attractiveness-related biases. We then respond to commentators who either misinterpreted some parts of our target article or made statements with which we disagree. These commentaries provided us with an opportunity to clarify (...) some aspects of our target article, for example, the fact that we address both the functional significance of attractiveness-related biases and their underlying mechanisms. We provide a rebuttal to two commentaries, in which we are accused of poor scholarship. We conclude our response by addressing two commentaries that discussed the societal implications of the occurrence of attractiveness-related biases in the labor market by briefly discussing the relationship between scientific research and social policy. (shrink)

Research with nonhuman primates can make important contributions to life history models of human attachment and reproductive strategies, such as: including parental responsiveness into female reproductive strategies, testing the assumption that adult attachment is a reproductive adaptation, assessing genetic and environmental effects on attachment and reproduction, and investigating the mechanisms through which early stress results in accelerated reproductive maturation.

The use of anecdotes is not a viable research strategy to study animal culture. Social learning processes can often be documented with careful quantitative analyses of observational data. Unfortunately, suggestions that killer whales engage in teaching are entirely based on subjective interpretations of qualitative observations. Thus, of teaching in killer whales cannot be used to argue for the occurrence of culture in marine mammals.

Recent evidence suggests that the ratio of the lengths of the second and fourth fingers (2D:4D) may reflect degree of prenatal androgen exposure in humans. In the present study, we tested the hypotheses that 2D:4D would be associated with ratings of men’s attractiveness and with levels of behavioral displays during social interactions with potential mates. Our results confirm that male 2D:4D was significantly negatively correlated with women’s ratings of men’s physical attractiveness and levels of courtship-like behavior during a brief conversation. (...) These findings provide novel evidence for the organizational effects of hormones on human male attractiveness and social behavior. (shrink)

Homology can provide strong evidence against exapted learning mechanism (ELM) explanations for psychological and behavioral traits. Homologous traits are constructed by commonly inherited developmental mechanisms. As such, demonstration of homology for a trait argues for its construction by an inherited rather than an exapted developmental process. We conclude that comparative evidence can play an important evidentiary role within evolutionary psychology.