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Research on emotion communication typically focuses on facial expressions, yet scientists dating back to Darwin have noted the importance of the body in conveying emotions. In fact, studies have found that the body is reliably used to express and recognize anger, fear, and sadness, by individuals in several industrialized populations. Here, we provide the first evidence that bodily expressions of these three emotions are reliably recognized by members of an isolated small-scale traditional society: the Mayangna of Nicaragua. Specifically, we found that recognition rates for sadness and anger bodily expressions were high, and recognition rates for a fear bodily expression were lower but still significantly greater than chance. Given that the Mayangna are unlikely to have learned these bodily expressions through cross-cultural transmission, their ability to recognize these displays provides strong evidence for the universality of each expression. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s42761-021-00052-y.

Funder: Max Planck Institute for Evolutionary Anthropology (2), A key issue distinguishing prominent evolutionary models of human life history is whether prolonged childhood evolved to facilitate learning in a skill- and strength-intensive foraging niche requiring high levels of cooperation. Considering the diversity of environments humans inhabit, children's activities should also reflect local social and ecological opportunities and constraints. To better understand our species' developmental plasticity, the present paper compiled a time allocation dataset for children and adolescents from twelve hunter-gatherer and mixed-subsistence forager societies (n = 690; 3-18 years; 52% girls). We investigated how environmental factors, local ecological risk, and men and women's relative energetic contributions were associated with cross-cultural variation in child and adolescent time allocation to childcare, food production, domestic work, and play. Annual precipitation, annual mean temperature, and net primary productivity were not strongly associated with child and adolescent activity budgets. Increased risk of encounters with dangerous animals and dehydration negatively predicted time allocation to childcare and domestic work, but not food production. Gender differences in child and adolescent activity budgets were stronger in societies where men made greater direct contributions to food production than women. We interpret these findings as suggesting that children and their caregivers adjust their activities to facilitate the early acquisition of knowledge which helps children safely cooperate with adults in a range of social and ecological environments. These findings compel us to consider how childhood may have also evolved to facilitate flexible participation in productive activities in early life.

Behavioral ecologists frequently use observational methods, such as instantaneous scan sampling, to record the behavior of animals at discrete moments in time. We develop and apply multilevel, multinomial logistic regression models for analyzing such data. These statistical methods correspond to the multinomial character of the response variable while also accounting for the repeated observations of individuals that characterize behavioral datasets. Correlated random effects potentially reveal individual-level trade-offs across behaviors, allowing for models that reveal the extent to which individuals who regularly engage in one behavior also exhibit relatively more or less of another behavior. Using an example dataset, we demonstrate the estimation of these models using Hamiltonian Monte Carlo algorithms, as implemented in the RStan package in the R statistical environment. The supplemental files include a coding script and data that demonstrate auxiliary functions to prepare the data, estimate the models, summarize the posterior samples, and generate figures that display model predictions. We discuss possible extensions to our approach, including models with random slopes to allow individual-level behavioral strategies to vary over time and the need for models that account for temporal autocorrelation. These models can potentially be applied to a broad class of statistical analyses by behavioral ecologists, focusing on other polytomous response variables, such as behavior, habitat choice, or emotional states. Electronic supplementary material The online version of this article (doi:10.1007/s00265-017-2363-8) contains supplementary material, which is available to authorized users.

When adult males are temporarily away from the household,observational evidence suggests cross-culturaland intra-cultural variation in the effects of their absence on the labor ofother householdmembers.Insubsistence-based econ- omies, we predict that other adolescent or older members will work more in essential production activities that otherwise would be performed by the missing men. We test this hypoth- esis using spot-check time allocation datasets from rural Nicaragua and Peru and the methodology of mixed-effects statistical models. In Nicaragua, we find that the absence of male household heads rarely necessitates substitute labor by household co-residents, apparently because men typically time their absences to coincide with the non-peak agricultural season. In Peru, the absence of male household heads results in increased men's work by co-residents only under unusual circumstances, as households apparently rely on other strate- gies to mitigate for the loss of labor. In addition to the com- parative empirical analysis of the two cases, we show how mixed-effects models allow for individual heterogeneity and data structures that confound more familiar statistical techni- ques and occasionally produce spurious results. Mixed-effects modeling techniques will be necessary if we are to realize the analytic potential of the extensive, standardized time al- location datasets gathered by anthropologists.

Recent analyses of food sharing in small-scale societies indicate that reciprocal altruism maintains interhousehold food transfers, even among close kin. In this study, matrix-based regression methods are used to test the explanatory power of reciprocal altruism, kin selection, and tolerated scrounging. In a network of 35 households in Nicaragua's Bosawas Reserve, the significant predictors of food sharing include kinship, interhousehold distance, and reciprocity. In particular, resources tend to flow from households with relatively more meat to closely related households with little, as predicted by kin selection. This generalization is especially true of household dyads with mother-offspring relationships, which suggests that studies of food sharing may benefit from distinctions between lineal and collateral kin. Overall, this analysis suggests that exchanges among kin are primarily associated with differences in need, not reciprocity. Finally, although large game is distributed widely, qualitative observations indicate that hunters typically do not relinquish control of the distribution in ways predicted by costly signaling theory.

By focusing on the caloric composition of hunted prey species, optimal foraging research has shown that hunters usually make economically rational prey choice decisions. However, research by meat scientists suggests that the gustatory appeal of wildlife meats may vary dramatically. In this study, behavioral research indicates that Mayangna and Miskito hunters in Nicaragua inconsistently pursue multiple prey types in the optimal diet set. We use cognitive methods, including unconstrained pile sorts and cultural consensus analysis, to investigate the hypothesis that these partial preferences are influenced by considerations of meat flavor. Native informants exhibit high agreement on the relative appeal of different meats. Given the absence of other noteworthy differences between spider monkeys (Ateles geoffroyi) and howler monkeys (Alouatta palliata), the unappealing flavor of howler monkeys seems to be a factor in the partial preference for this species.