The evolution of food sharing in primates

The aim of this study is to explain the occurrence of food sharing across primates. Defined as the unresisted transfer of food, evolutionary hypotheses have to explain why possessors should relinquish food rather than keep it. While sharing with offspring can be explained by kin selection, explanations for sharing among unrelated adults are more controversial. Here we test the hypothesis that sharing occurs with social partners that have leverage over food possessors due to the opportunity for partner choice in other contexts. Thus, we predict that possessors should relinquish food to potential mates or allies, who could provide or withhold matings or coalitionary support in the future. We used phylogenetic analyses based on both maximum likelihood and Bayesian approaches in a sample of 68 primate species to test these predictions. The analyses strongly indicate that (1) sharing with offspring is predicted by the relative processing difficulty of the diet, as measured by the degree of extractive foraging, but not overall diet quality, (2) food sharing among adults only evolved in species already sharing with offspring, regardless of diet, and (3) male-female sharing co-evolved with the opportunity for female mate choice and sharing within the sexes with coalition formation. These results provide comparative support for the hypothesis that sharing is "traded” for matings and coalitionary support in the sense that these services are statistically associated and can thus be selected for. Based on this, we predict that sharing should occur in any species with opportunities for partner choic

Specialised minds: extending adaptive explanations of personality to the evolution of psychopathology

Traditional evolutionary theory invoked natural and sexual selection to explain species- and sex-typical traits. However, some heritable inter-individual variability in behaviour and psychology – personality – is probably adaptive. Here we extend this insight to common psychopathological traits. Reviewing key findings from three background areas of importance – theoretical models, non-human personality and evolved human social dynamics – we propose that a combination of social niche specialisation, negative frequency-dependency, balancing selection and adaptive developmental plasticity should explain adaptation for individual differences in psychology – ‘specialised minds’ – explaining some variance in personality and psychopathology trait dimensions, which share various characteristics. We suggest that anthropological research of behavioural differences should be extended past broad demographic factors (age and sex) to include individual specialisations. As a first step towards grounding psychopathology in ancestral social structure, we propose a minimum plausible prevalence, given likely ancestral group sizes, for negatively frequency-dependent phenotypes to be maintained as specialised tails of adaptive distributions – below the calculated prevalence, specialisation is highly unlikely. For instance, chronic highly debilitating forms of autism or schizophrenia are too rare for such explanations, whereas attention-deficit-hyperactivity disorder and broad autism phenotypes are common enough to have existed in most hunter-gatherer bands, making adaptive explanations more plausible

Oxytocin levels tend to be lower in autistic children: A meta-analysis of 31 studies

The oxytocin system may be different in autistic people, which could explain some of the deficits in social behavior and cognition associated with autism spectrum disorder. However, studies comparing oxytocin levels in autistic and neurotypical individuals have shown conflicting results and a 2016 meta-analysis on seven studies concluded that there was no significant difference. Here, we greatly expanded the sample of studies to 31, warranting a reassessment of this finding. We searched Web of Science with MEDLINE$^{®}$, SciELO Citation Index, and BIOSIS Citation Index for articles that measured oxytocin in plasma/serum ( k = 26 studies), saliva (4), or cerebrospinal fluid (1) in autistic individuals (total n = 1233 participants) compared to neurotypical individuals ( n = 1304). We found that oxytocin levels were significantly lower in autistic people (Cohen’s d = −0.36, 95% confidence interval = [−0.61, −0.10], p = 0.007), with no evidence for publication bias. This overall effect was driven entirely by differences among children ( k = 25, d = −0.44, 95% confidence interval = [−0.72, −0.16], p = 0.002) but not adults ( k = 6, d = 0.03, 95% confidence interval = [−0.55, 0.61], p = 0.92). These results support further research into the use of oxytocin to treat social deficits in children. Lay abstract Oxytocin is a hormone that mediates interpersonal relationships through enhancing social recognition, social memory, and reducing stress. It is released centrally into the cerebrospinal fluid, as well as peripherally into the blood, where it can easily be measured. Some studies indicate that the oxytocin system with its social implications might be different in people with autism spectrum disorder. With summarizing evidence of 31 studies, this meta-analysis suggests that children with autism spectrum disorder have lower blood oxytocin levels compared to neurotypical individuals. This might not be the case for adults with autism spectrum disorder, where we could not find a difference. Our findings motivate further exploration of the oxytocin system in children with autism spectrum disorder. This could lead to therapeutic options in treating autism spectrum disorder in childhood

The social evolution of individual differences: Future directions for a comparative science of personality in social behavior

Personality is essential for understanding the evolution of cooperation and conflict in behavior. However, per-sonality science remains disconnected from the field of social evolution, limiting our ability to explain how personality and plasticity shape phenotypic adaptation in social behavior. Researchers also lack an integrative framework for comparing personality in the contextualized and multifaceted behaviors central to social in-teractions among humans and other animals. Here we address these challenges by developing a social evolu-tionary approach to personality, synthesizing theory, methods, and organizing questions in the study of individuality and sociality in behavior. We critically review current measurement practices and introduce social reaction norm models for comparative research on the evolution of personality in social environments. These models demonstrate that social plasticity affects the heritable variance of personality, and that individual dif-ferences in social plasticity can further modify the rate and direction of adaptive social evolution. Future empirical studies of frequency-and density-dependent social selection on personality are crucial for further developing this framework and testing adaptive theory of social niche specialization.Peer reviewe

An Antidote to Overpathologizing Computer-Mediated Communication: An Evolutionary Perspective on Mixed Effects of Mismatch

Mixed associations are recurrently found between computer-mediated communication (CMC) and mental health & well-being. Recently, different theoretical efforts have emerged to parse these mixed results. However, evolutionary considerations in such efforts remain largely on the periphery, despite fields like evolutionary medicine and anthropology often theorising about mental health problems arising due to evolutionarily novel environmental circumstances: so-called evolutionary mismatch. While certain aspects of CMC have been previously identified as plausible evolutionary mismatches, two important limitations emerge: (a) a failure to contextualise the negative mental health effects of CMC against other broader societal factors which are plausible pre-existing evolutionary mismatches themselves; (b) ignoring the positive effects of CMC in mitigating these mismatches. In this paper, we propose an evolutionary perspective that addresses these two limitations while noting distinct epistemic and empirical benefits of such a perspective (e.g. providing a culturally invariant theory-driven baseline of ‘normal behaviour’, renewed theoretical focus on alternative variables, concrete design recommendations). Importantly, we contend that our perspective serves as an antidote to the overpathologisation of novel behaviours facilitated by CMC by framing such behaviours within the hunter-gatherer social environment characterising the majority of our evolutionary history

Physical Activity and Modernization Among Bolivian Amerindians

Background: Physical inactivity is a growing public health problem, and the fourth leading risk factor for global mortality. Conversely, indigenous populations living traditional lifestyles reportedly engage in vigorous daily activity that is protective against non-communicable diseases. Here we analyze physical activity patterns among the Tsimane, forager-horticulturalists of Amazonian Bolivia with minimal heart disease and diabetes. We assess age patterns of adult activity among men and women, test whether modernization affects activity levels, and examine whether nascent obesity is associated with reduced activity. Methods and Findings: A factorial method based on a large sample of behavioral observations was employed to estimate effects of age, sex, body mass index, and modernization variables on physical activity ratio (PAR), the ratio of total energy expenditure to basal metabolic rate. Accelerometry combined with heart rate monitoring was compared to the factorial method and used for nighttime sampling. Tsimane men and women display 24 hr physical activity level (PAL) of 2.02–2.15 and 1.73–1.85, respectively. Little time was spent ‘‘sedentary’’, whereas most activity was light to moderate, rather than vigorous. Activity peaks by the late twenties in men, and declines thereafter, but remains constant among women after the early teens. Neither BMI, fat free mass or body fat percentage are associated with PAR. There was no negative effect of modernization on physical activity. Conclusions: Tsimane display relatively high PALs typical of other subsistence populations, but of moderate intensity, and not outside the range of developed populations. Despite rapidly increasing socioeconomic change, there is little evidence that total activity has yet been affected. Overweight and obesity are more prevalent among women than men, and Spanish fluency is associated with greater obesity in women. The lack of cardiovascular disease among Tsimane is unlikely caused by activity alone; further study of diet, food intake and infectious disease is needed

Impact of Prenatal Stress on Offspring Glucocorticoid Levels: A Phylogenetic Meta-analysis Across 14 Vertebrate Species

Prenatal exposure to maternal stress is commonly associated with variation in Hypothalamic Pituitary Adrenal (HPA)-axis functioning in ofspring. However, the strength or consistency of this response has never been empirically evaluated across vertebrate species. Here we meta-analyzed 114 results from 39 studies across 14 vertebrate species using Bayesian phylogenetic mixed-efects models. We found a positive overall efect of prenatal stress on ofspring glucocorticoids (d’=0.43) though the 95% Highest Posterior Density Interval overlapped with 0 (−0.16–0.95). Meta-regressions of potential moderators highlighted that phylogeny and life history variables predicted relatively little variation in efect size. Experimental studies (d’=0.64) produced stronger efects than observational ones (d’=−0.01), while prenatal stress afected glucocorticoid recovery following ofspring stress exposure more strongly (d’=0.75) than baseline levels (d’=0.48) or glucocorticoid peak response (d’=0.36). These fndings are consistent with the argument that HPA-axis sensitivity to prenatal stress is evolutionarily ancient and occurs regardless of a species’ overall life history strategy. These efects may therefore be especially important for mediating intra-specifc life-history variation. In addition, these fndings suggest that animal models of prenatal HPA-axis programming may be appropriate for studying similar efects in humans

Sex differences in cooperative coalitions: a mammalian perspective

In group-living species, cooperative tactics can offset asymmetries in resource-holding potential between individuals and alter the outcome of intragroup conflicts. Differences in the kinds of competitive pressures that males and females face might influence the benefits they gain from forming intragroup coalitions. We predicted that there would be a female bias in intragroup coalitions because females (1) are more like to live with kin than males are, and (2) compete over resources that are more readily shared than resources males compete over. We tested this main prediction using information about coalition formation across mammalian species and phylogenetic comparative analyses. We found that for nearly all species in which intragroup coalitions occur, members of both sexes participate, making this the typical mammalian pattern. The presence and frequency of female or male coalitions were not strongly associated with key socio-ecological factors like resource defensibility, sexual dimorphism or philopatry. This suggests that once the ability to form intragroup coalitions emerges in one sex, it is likely to emerge in the other sex as well and that there is no strong phylogenetic legacy of sex differences in this form of cooperation. This article is part of the theme issue ‘Cooperation among women: evolutionary and cross-cultural perspectives’