Evolution and Human Behavior最新文献

This study investigates the hypothesis that perinatal depression could function as a catalyst for a mother to elicit cooperation from others in times of need (Hagen, 2002). We analyze data on social support and depression from 292 women in Uganda around the time of giving birth and find that a perceived lack of support, especially from the baby's father, is linked to a higher risk of depression in the mother. Moreover, we employ a quasi-experimental strategy to analyze the lesser-studied direction of the causality and estimate the effect of perinatal depression on different types of support (instrumental, informational, emotional, economic) a mother receives from kin, affines, and unrelated individuals. The results indicate that mothers at the threshold of depression obtain increased help from several individuals, especially the baby's father. Others who show a positive reaction include the woman's mother (maternal grandmother), father (maternal grandfather), and, to a minor extent, father-in-law (paternal grandfather), and cousins. Unrelated but physically close individuals (neighbors and friends) generally provide substantial help but do not react at the depression threshold. Overall, our findings provide some evidence in favor of the bargaining hypothesis for maternal depression.

The immunocompetence handicap hypothesis (ICHH) contends that testosterone-dependent, masculine traits are honest signals of the bearer's ability to withstand immunosuppression, yet empirical studies testing the ICHH have produced mixed results. The present research addressed the relationship between masculine vocal parameters and immunity in two samples: young adult men from the US and Canada (N = 267) and adolescent males from Bolivia (N = 44). All participants provided saliva samples, assayed for a biomarker of mucosal immunity associated with respiratory disease resistance: secretory immunoglobulin-A (sIgA). Participants also contributed speech samples, analyzed for two sexually dimorphic aspects of the human voice: 1) fundamental frequency (f_o; perceived as pitch) and vocal tract length (VTL; estimated using formant frequencies). Multiple regression models were used to assess the association between masculine vocal parameters and sIgA. Results indicated that lower f_o and longer VTL were associated with higher sIgA levels. That is, both adult and adolescent males with more masculine voices showed better mucosal immunity (and therefore disease resistance) than those with less masculine voices. Although this accords with several previous studies on voice and sIgA, it contrasts with standard ICHH-derived predictions. We suggest that life-history theory provides a better conceptual framework for understanding the association between testosterone-dependent secondary sexual characteristics and immunity as it shifts the focus from immunosuppression to efficient immunoredistribution.

We discuss gendered division of labour in nuclear households as a bargaining problem, where male and female partners bargain over labour inputs and resulting leisure time. We hypothesize that outside options - an individual's fallback options for welfare outside their household, such as kin support - affects this bargaining process, providing those with greater outside options more leverage to bargain for leisure time. In two hunter-gatherer populations, the BaYaka and Agta, we take social capital as the determinant of outside options, using a generative model of the Nash bargaining problem and Bayesian multilevel logistic regression to test our hypothesis. We find no evidence for an association between social capital and division of leisure in either population. Instead, we find remarkable equality in the division of leisure time within households. We suggest the potential role of sex-egalitarian norms, non-substitutability of subsistence labour, bilocality and behaviours which maintain gender equality in immediate-return hunter-gatherers.

Despite the indisputable significance of human symbolic cognition and behavior, we still lack a detailed understanding of the mechanisms by which such capacities evolved during the Paleolithic. An important source of evidence is constituted by archaeological findings of intentional markings left on rock and bone surfaces, but these are often opaque with respect to their original meaning and function. Here we present experimental work that systematically addresses the relation between properties of intentional markings and their cognitive implications to support inferences about their past functions. Participants reproduced engraved markings dating to c. 100.000 years ago from the South African Blombos and Diepkloof sites in three conditions of cultural transmission: as part of an aesthetic, identity marking, and communicative activity. Their reproductions were then used as stimuli in a suite of five perceptual experiments to investigate differences in their cognitive implications over time and explore similarities with the archaeological record.

Why are women underrepresented in positions of leadership? According to the “think manager-think male” model, leaders are stereotyped as male—and, in turn, as dominant—and this stereotype translates into preferences. However, status and leadership can be attained not only by dominance but also by prestige—a less sex-typed pathway. Five studies explored the relationship between leader stereotypes and preferences. University students spontaneously imagined both dominant and prestigious leaders as men (Study 1A, N = 148)—and this generalized across occupational domains (Study 1B, N = 220). However, they preferred women and prestigious leaders over men and dominant leaders. Study 2 (N = 2692) found this preference for female over male leaders using a large nationally representative U.S. sample from the Pew American Trends Panel. Study 3 (N = 461) experimentally replicated the preference for prestigious female over dominant male leader candidates among university students. In Study 4, (N = 952) online MTurk participants judged politicians from face photographs and again showed a preference for women, which may have partially been due to the inference that women are more likely to use prestige- over dominance-based leadership strategies. Collectively, findings suggest that the belief that people prefer “alpha male” leaders, which might discourage women from pursuing leadership roles and others from nominating them, needs to be updated.