Evolution and Human Behavior最新文献

The adaptive benefits of cooperation among humans have been widely studied. However, is being cooperative always adaptive across various combinations of ecological conditions? Existing work has focused on cultural, inter-, and intra-individual predictors of cooperation yet there is a lack of research on how an individual's ecology may come into play. In this work, we focus on the interaction of two ecological factors—population density and resource scarcity—on cooperation. Population density is often accompanied by social competition for limited resources. We hypothesise that in response to cues of high (versus low) population density, people facing resource-scarcity would adaptively lower their cooperativeness, more so than those with resource abundance. Results from two studies support our hypothesis—population density lowers cooperation, but only for people who perceive lower resources or social status. Our findings provide insights that cooperation varies adaptively as a function of interacting ecological factors.

Gendered divisions of labor are a feature of every known contemporary hunter-gatherer (forager) society. While gender roles are certainly flexible, and prominent and well-studied cases of female hunting do exist, it is more often men who hunt. A new study (Anderson et al., 2023) surveyed ethnographically known foragers and found that women hunt in 79% of foraging societies, with big-game hunting occurring in 33%. Based on this single type of labor, which is one among dozens performed in foraging societies, the authors question the existence of gendered division of labor altogether. As a diverse group of hunter-gatherer experts, we find that claims that foraging societies lack or have weak gendered divisions of labor are contradicted by empirical evidence. We conducted an in-depth examination of the data and methods of Anderson et al. (2023), finding evidence of sample selection bias and numerous coding errors undermining the paper's conclusions. Anderson et al. (2023) have started a useful dialogue to ameliorate the potential misconception that women never hunt. However, their analysis does not contradict the wide body of empirical evidence for gendered divisions of labor in foraging societies. Furthermore, a myopic focus on hunting diminishes the value of contributions that take different forms and downplays the trade-offs foragers of both sexes routinely face. We caution against ethnographic revisionism that projects Westernized conceptions of labor and its value onto foraging societies.

Trait inferences from faces are pervasive, but sometimes misleading. Past research indicates Americans infer hunting and gathering ability from others' faces, but the accuracy of these perceptions remains unknown. In three studies, we test whether Americans can accurately perceive foraging ability from faces. We used three datasets from two traditional subsistence societies (the Hadza and the Tsimane) in which individuals were photographed and evaluated by their peers on their ability to hunt or gather effectively (N = 175). US MTurkers (N = 579) then evaluated the photos for foraging ability. We found that MTurkers' perceptions of men consistently tracked peer-evaluated hunting ability (overall r = 0.25), suggesting that naïve perceptions of men's productivity from a face photo alone reflect actual hunting ability. MTurkers' perceptions of women's productivity inversely correlated with their peer-evaluated gathering ability, however. We discuss potential mechanisms and implications for research on social perception.

Cross-sectional studies suggest that local ecological knowledge (LEK) helps humans cope with their environment. Among the forms of LEK, adult knowledge of wild plants has been associated with better child and adult health. We assess if the concurrent links between i) LEK and ii) health and nutritional status last and examine if LEK yields delayed benefits when societies face large socioeconomic and environmental changes. We use a yearly panel (2002−2010) from Tsimane’, an Indigenous Amazonian society (Bolivia). All adults (∼440) and children (∼300) measured at baseline (2003) in 13 villages were followed yearly during 2004–2010 to estimate associations between a) baseline adult knowledge and skill about uses of wild plants and b) subsequent (2004–2010) anthropometric markers of nutritional status of themselves and the children (2y ≤ age ≤ 10y) living in the household at baseline. Among children, HAZ, BMI, and sum of four skinfolds were measured; among adults, BMI, sum of four skinfolds, and percent body fat with bioelectrical impedance were measured. Some skill losses increased by a large amount the likelihood of severe childhood stunting (HAZ < -3) for girls; the complete loss of these skills increased the share of severely stunted girls from 5% to 13%–20%. These are big numbers. The effects of LEK on other anthropometric indicators of children or adults were small. For example, if all adults in a household lost all their ethnobotanical knowledge, children's and women's BMI would decrease by only 3% and 11%, respectively.

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.