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Humans are motivated to compete for access to valuable social partners, which is a function of their willingness to share and ability to generate resources. However, relative preferences for each trait should be responsive to socioecological conditions. Here, we test the flexibility of partner choice psychology among Hadza hunter–gatherers of Tanzania. Ninety-two Hadza ranked their campmates on generosity and foraging ability and then shared resources with those campmates. We found Hadza with greater exposure to other cultures shared more with campmates ranked higher on generosity, whereas Hadza with lower exposure showed a smaller preference for sharing with generous campmates. This moderating effect was specific to generosity—regardless of exposure, Hadza showed only a small preference for sharing with better foragers. We argue this difference in preferences is due to high exposure Hadza having more experience cooperating with others in the absence of strong norms of sharing, and thus are exposed to greater variance in willingness to cooperate among potential partners increasing the benefits of choosing partners based on generosity. As such, participants place a greater emphasis on choosing more generous partners, highlighting the flexibility of partner preferences.

Humans’ willingness to bear costs to benefit others is an evolutionary puzzle. Cultural group selection proposes a possible answer to this puzzle—cooperative norms and institutions proliferate due to group-level benefits. For instance, belief in knowledgeable, moralizing deities is theorized to decrease selfishness and favoritism through threat of supernatural punishment. Similarly, norms of fairness and cooperation are theorized to have coevolved with engagement in markets, which necessitate anonymous exchanges. We investigate these theories among the Tanzanian Hadza who, until recently, have had minimal exposure to markets or major world religions. Engagement with Western tourists, village markets, and Christian missionaries is increasingly leading researchers to ask how such interactions have affected cooperative behavior. We interviewed 172 Hadza from 15 camps varying in market proximity, and measured cooperative decision-making using economic games. We find that exposure to missionaries is associated with increased belief in a knowledgeable and punitive deity, with mixed evidence that these beliefs, in turn, affect game play. In contrast, we find some evidence that those living in market-adjacent regions exhibit less in-group favoritism when cooperating. These results support the claim that market-norms, and to some degree religious beliefs, facilitate greater cooperation and fairness in social interactions.

Myopia rates are increasing globally. This epidemic is linked to increased school participation, decreased outdoor activity and the proliferation of near-work occupations. The Tanzanian Hadza have traditionally subsisted as hunter-gatherers. School participation has historically been low and near-work otherwise minimal. Previous studies have reported exceptionally low myopia rates among hunter-gatherers, though such studies are few. The present study aims to expand this dataset. We report Hadza myopia rates and compare them to those from other economic/subsistence niches. We look for temporal changes in eyesight, in line with changing Hadza subsistence. Further, we assess the impact two known myopia risk factors, gender and educational participation, on Hadza eyesight. Materials and Methods We measured visual acuity among 182 bush-living Hadza aged 10–75 using a non-Latin optotype. From these measures, we estimate age-specific myopia prevalences. Results We find age-specific myopia prevalences between 5% and 10% for individuals under 40, increasing thereafter. This is low compared to industrialized populations, although not atypical for rural and non-industrialized populations. Unlike previous studies of hunter-gatherers, myopia was not exceptionally rare. We find that Hadza men have better distance vision than Hadza women. Though the Hadza have experienced subsistence change, we find no statistical evidence of associated decreases in visual acuity between 2006 and 2013/14 after controlling for gender imbalances. Finally, we find no support for our prediction that schooling participation reduces visual acuity, though so few attended school (13 of 58) that this analysis lacked statistical power and probably represents a false negative.

The ability to choose the partners we interact with is thought to have been an important driver in the evolution of human social behavior, and in particular, our propensity to cooperate. Studies showing that humans prefer to interact with cooperative others is often cited as support for partner choice driving the evolution of cooperation. However, these studies are largely drawn from Western samples, where conditions for partner choice to operate may be especially favorable. Here, we investigate qualities associated with being a preferred partner (i.e., campmate) in Hadza hunter-gatherers of Tanzania in 2016 and 2019. A total of 156 Hadza participants from 17 camps ranked their campmates on generosity, foraging ability, and their preference for them as future campmates. In 2016, Hadza preferred more generous people and better hunters as campmates, with evidence suggesting a stronger preference for better hunters; however, the relationship between generosity and being a preferred campmate was greater in 2019 than in 2016, such that the preference for generous people was stronger than the preference for better foragers, suggesting that campmate preferences are changing. These new findings contrast with reports on data from nearly a decade ago, suggesting that the Hadza do not prefer more cooperative campmates. Further, in 2019, there was anecdotal evidence that Hadza with greater exposure to outside cultural institutions (e.g., schooling, having a job, or living in a village) had a stronger preference for generous campmates than those with less exposure. Taken together, the results suggest that preferences for social partners may, in part, be culturally shaped.

Supplemental material is available online at https://www.tandfonline.com/doi/full/10.1080/2153599X.2021.2006292#supplemental-material-section . Scholars of religion have long sought to explain the persistent finding that women tend to report greater religiosity than men. However, the size of this “gender gap” may depend on the measure of religiosity employed, the religious tradition being sampled, and socio-demographic factors. Here, we conduct a systematic cross-cultural investigation into the prevalence of, and explanations for, the religiosity gender gap in 2,002 individuals from 14 diverse societies. While variation exists across societies, women in general indicate greater mental commitment (i.e., thinking and worrying more about) to their community’s moralistic god, more frequent participation in rituals for their community’s moralistic god, and more frequent prayer. While we find that the gender gap extends beyond the Christian world, no such difference was seen in religious commitment towards more local gods, to which men tend to show greater commitment. Tentative support is provided for explanations relating gender differences in religiosity to lower formal education and greater mentalizing among women, however an explanation for greater religious commitment to local gods among men remains elusive. Nevertheless, our data suggest that the moralizing gods of some contemporary world religions, unlike local deities and traditions, have evolved in ways that make them more appealing to women. Royal Society Te Apārangi Rutherford Discovery Fellowship: [Grant Number RDF-UOA1101]; Social Sciences and Humanities Research Council of Canada: [Grant Number 895-2011-1009].

Researchers hypothesize that social selection resulting from partner choice may have shaped deontological moral reasoning in humans. People in Western societies judge deontologists to be more trustworthy than utilitarians and prefer them as cooperative partners. We test if the preference for deontologists as social partners generalizes to the Hadza, hunter-gatherers residing in Tanzania. We presented 134 Hadza participants with three ecologically-relevant sacrificial dilemmas and asked them to judge whether the actor should sacrifice one person to save five. We then randomly assigned participants to hear that the actor made either a deontological or utilitarian decision and asked them to make partner choice judgments about the actor in the dilemma. Compared to 249 US Mechanical Turk participants, Hadza participants were more likely to think the actor should choose the utilitarian option. Regardless of what option they thought the actor should choose, Hadza participants showed no preference for the deontological or utilitarian decision-maker, whereas Mechanical Turk participants who thought the actor should choose the deontological option had a strong preference for the deontological actor. These results suggest the preference for deontological decision-makers as cooperative partners is culturally variable.

The phenomenon of magical contagion – the unobserved passage of properties between entities that come into physical contact – was described by anthropologists over a century ago, yet questions remain about its origin, function, and universality. Contagion sensitivity, along with the emotion of disgust, has been proposed to be part of a biologically-evolved system designed to reduce exposure to pathogens by increasing the avoidance of "contaminated" objects. Yet this phenomenon has not been studied using systematic psychological comparison outside of industrialized populations. Here we document contagion sensitivity in two culturally, geographically, and economically distinct populations with little exposure to Western biomedicine and formal education: the Hadza hunter-gatherers of Tanzania and Tannese subsistence-agriculturalists of Vanuatu. In both populations, a majority of individuals rejected familiar and palatable foods when contaminating items touched the food but were subsequently removed. The Tannese children in our study showed a similar response, consistent with previous research with Western children. Our data support the proposal that contagion sensitivity is universal in human populations.

Chemical communication plays an important role in the social interactions and mating behavior of diverse animal taxa; yet its role in humans remains equivocal. Using a randomized, placebo-controlled experiment involving 243 male participants, we test whether exposure to synthetic copulin – a mixture of volatile fatty acids secreted vaginally in primates, increases 1) men’s sexual motivation using an incentivized behavioral task, 2) self-reported willingness to take sexual risks, 3) preference for short-term mating, 4) perceptions of female attractiveness and 5) self-reported mate value. Because chemical receptors are found throughout the body and human chemosensory pathways have yet to be definitively identified, we also manipulate the location of copulin exposure (i.e. olfactory epithelium versus epidermal keratinocytes in the genital region). Finally, we examine whether prior sexual experience mediate any behavioral effects. Unlike previous reports, we fail to find any effects of copulin exposure on measures of men’s sexual behavior.

Observed economic and labor disparities between the sexes may, in part, result from evolved sex differences in risk preferences. Using incentivized economic games, we report on sex differences in risk preferences in the Hadza, a population of hunter-gatherers. One game played in 2010 (n=233) found that more Hadza males than females prefer to gamble for a chance to earn more maize rather than settle for a sure, but smaller, amount. Similarly, a second game played in 2013 (n=102) found that male Hadza gamble a greater proportion of honey for a chance to earn more compared to female Hadza. Effect sizes are small to medium. We find weak evidence that risk-taking increases in men as their mating opportunities increase. In both games, the sex difference widens throughout childhood and is greatest among adolescents; though note that child samples are small. We explore developmental trends further using observational data on food returns in children (n=357). Our data suggest that while the mean number of calories boys bring to camp remains stable with age, the variance in their caloric returns increases. Among girls, the variance remains stable with increased age. Both the economic games and food return data are consistent with the sexual division of labor wherein boys, beginning in late childhood, begin to target riskier foods. To the extent that the Hadza allow us to make inferences about long-standing patterns of human behavior, we suggest that sex differences in risk preferences may have been present long before agriculture and the modern work environment.

We report on two experiments investigating whether there is a gender difference in the willingness to compete against oneself (self-competition), similar to what is found when competing against others (other-competition). In one laboratory and one online market experiment, involving a total of 1,200 participants, we replicate the gender-gap in willingness to other-compete but find no evidence of a gender difference in the willingness to self-compete. We explore the roles of risk and confidence and suggest that these factors can account for the different findings. Finally, we document that self-competition does no worse than other-competition in terms of performance boosting.

Fluctuating asymmetry (FA), deviation from perfect bilateral symmetry, is thought to reflect an organism's relative inability to maintain stable morphological development in the face of environmental and genetic stressors. Previous research has documented negative relationships between FA and attractiveness judgments in humans, but scant research has explored relationships between the human voice and this putative marker of genetic quality in either sex. Only one study (and in women only) has explored relationships between vocal attractiveness and asymmetry of the face, a feature-rich trait space central in prior work on human genetic quality and mate choice. We therefore examined this relationship in three studies comprising 231 men and 240 women from two Western samples as well as Hadza hunter-gatherers of Tanzania. Voice recordings were collected and rated for attractiveness, and FA was computed from two-dimensional facial images as well as, for a subset of men, three-dimensional facial scans. Through meta-analysis of our results and those of prior studies, we found a negative association between FA and vocal attractiveness that was highly robust and statistically significant whether we included effect sizes from previously published work, or only those from the present research, and regardless of the inclusion of any individual sample or method of assessing FA (e.g., facial or limb FA). Weighted mean correlations between FA and vocal attractiveness across studies were -.23 for men and -.29 for women. This research thus offers strong support for the hypothesis that voices provide cues to genetic quality in humans.

Darwin viewed cooperation as a perplexing challenge to his theory of natural selection. Natural selection generally favors the evolution of behaviors that enhance the fitness of individuals. Cooperative behavior, which increases the fitness of a recipient at the expense of the donor, contradicts this logic. William D. Hamilton helped to solve the puzzle when he showed that cooperation can evolve if cooperators direct benefits selectively to other cooperators (i.e. assortment). Kinship, group selection and the previous behavior of social partners all provide mechanisms for assortment (Figure 1), and kin selection and reciprocal altruism are the foundation of the kinds of cooperative behavior observed in many animals. Humans also bias cooperation in favor of kin and reciprocating partners, but the scope, scale, and variability of human cooperation greatly exceed that of other animals. Here, we introduce derived features of human cooperation in the context in which they originally evolved, and discuss the processes that may have shaped the evolution of our remarkable capacity for cooperation. We argue that culturally-evolved norms that specify how people should behave provide an evolutionarily novel mechanism for assortment, and play an important role in sustaining derived properties of cooperation in human groups.

To the extent that moral character is grounded in stable and observable truths, there should exist agreement between people in their judgments of others’ character. In Western populations, this agreement is found. We examine whether this is universal in Hadza hunter-gatherers of Tanzania. Ninety-four judges ranked their campmates on global character and relevant character traits for a total of 802 observations. Judges disagreed on rankings of global character, generosity, and honesty but agreed more on hard work and hunting ability. Individual rankings on specific traits predicted character evaluations. There was agreement between judges on the extent to which generosity and hard work related to character. These findings suggest that Hadza have shared beliefs about what traits constitute character but disagree on which of their campmates exhibit these traits. We discuss these findings in light of other research suggesting that stable moral dispositions may not be universal.

The data set used for the current analyses together with protocols, hypotheses, and R code can be found at the Open Science Framework (https://osf.io/epkbw/). © 2019 The Author(s). xThe emergence of large-scale cooperation during the Holocene remains a central problem in the evolutionary literature. One hypothesis points to culturally evolved beliefs in punishing, interventionist gods that facilitate the extension of cooperative behaviour toward geographically distant co-religionists. Furthermore, another hypothesis points to such mechanisms being constrained to the religious ingroup, possibly at the expense of religious outgroups. To test these hypotheses, we administered two behavioural experiments and a set of interviews to a sample of 2228 participants from 15 diverse populations. These populations included foragers, pastoralists, horticulturalists, and wage labourers, practicing Buddhism, Christianity, and Hinduism, but also forms of animism and ancestor worship. Using the Random Allocation Game (RAG) and the Dictator Game (DG) in which individuals allocated money between themselves, local and geographically distant co-religionists, and religious outgroups, we found that higher ratings of gods as monitoring and punishing predicted decreased local favouritism (RAGs) and increased resource-sharing with distant co-religionists (DGs). The effects of punishing and monitoring gods on outgroup allocations revealed between-site variability, suggesting that in the absence of intergroup hostility, moralizing gods may be implicated in cooperative behaviour toward outgroups. These results provide support for the hypothesis that beliefs in monitoring and punitive gods help expand the circle of sustainable social interaction, and open questions about the treatment of religious outgroups. John Templeton Foundation; Cultural Evolution of Religion Research Consortium (CERC); Social Sciences and Humanities Research Council of Canada

Laughter is a nonverbal vocal expression that often communicates positive affect and cooperative intent in humans. Temporally coincident laughter occurring within groups is a potentially rich cue of affiliation to overhearers. We examined listeners’ judgments of affiliation based on brief, decontextualized instances of colaughter between either established friends or recently acquainted strangers. In a sample of 966 participants from 24 societies, people reliably distinguished friends from strangers with an accuracy of 53–67%. Acoustic analyses of the individual laughter segments revealed that, across cultures, listeners’ judgments were consistently predicted by voicing dynamics, suggesting perceptual sensitivity to emotionally triggered spontaneous production. Colaughter affords rapid and accurate appraisals of affiliation that transcend cultural and linguistic boundaries, and may constitute a universal means of signaling cooperative relationships.

We study the willingness to compete against self and others in an experiment with over 650 participants, using a modified version of the Niederle and Vesterlund (2007) design. We show that introducing a possibility to self-compete, in addition to the standard other-competition option, increases the proportion of participants who compete by more than 60 percent, indicating that self-competition attracts many of those who would otherwise have stayed out of competitions altogether. This holds for both men and women. Moreover, men and women prefer self-competitions to other-competitions, especially when they have to select one of the two types of competitions. We also document that self-competitions are perceived as more controllable than other-competitions.

© 2018 Elsevier Inc. Does moral culture contribute to the evolution of cooperation? Here, we examine individuals’ and communities’ models of what it means to be good and bad and how they correspond to corollary behavior across a variety of socioecological contexts. Our sample includes over 600 people from eight different field sites that include foragers, horticulturalists, herders, and the fully market-reliant. We first examine the universals and particulars of explicit moral models. We then use these moral models to assess their role in the outcome of an economic experiment designed to detect systematic, dishonest rule-breaking favoritism. We show that individuals are slightly more inclined to play by the rules when their moral models include the task-relevant virtues of “honesty” and “dishonesty.” We also find that religious beliefs are better predictors of honest play than these virtues. The predictive power of these values’ and beliefs’ local prevalence, however, remains inconclusive. In summary, we find that religious beliefs and moral models may help promote honest behavior that may widen the breadth of human cooperation. SSHRC partnership grant; the John Templeton Foundation; the Max Planck Institute for Evolutionary Anthropology (MPI)

Summary Widespread cooperation is a defining feature of human societies from hunter-gatherer bands to nation states [ 1 , 2 ], but explaining its evolution remains a challenge. Although positive assortment of cooperators is recognized as a basic requirement for the evolution of cooperation, the mechanisms governing assortment are debated. Moreover, the social structure of modern hunter-gatherers, characterized by high mobility, residential mixing, and low genetic relatedness [ 3 ], undermines assortment and adds to the puzzle of how cooperation evolved. Here, we analyze four years of data (2010, 2013, 2014, 2016) tracking residence and levels of cooperation elicited from a public goods game in Hadza hunter-gatherers of Tanzania. Data were collected from 56 camps, comprising 383 unique individuals, 137 of whom we have data for two or more years. Despite significant residential mixing, we observe a robust pattern of assortment that is necessary for cooperation to evolve; in every year, Hadza camps exhibit high between-camp and low within-camp variation in cooperation. We find little evidence that cooperative behavior within individuals is stable over time or that similarity in cooperation between dyads predicts their future cohabitation. Both sets of findings are inconsistent with models that assume stable cooperative and selfish types, including partner choice models. Consistent with social norms, culture, and reciprocity theories, the strongest predictor of an individual’s level of cooperation is the mean cooperation of their current campmates. These findings underscore the adaptive nature of human cooperation—particularly its responsiveness to social contexts—as a feature that is important in generating the assortment necessary for cooperation to evolve.

SUMMARYWidespread cooperation is a defining feature of human societies from hunter-gatherer bands to nation states. But explaining its evolution remains a challenge. While positive assortment – of cooperators with cooperators – is recognized as a basic requirement for the evolution of cooperation, the mechanisms governing assortment are debated. Moreover, the social structure of modern hunter-gatherers, characterized by high mobility, residential mixing and low genetic relatedness, undermine assortment and add to the puzzle of how cooperation evolved. Here, we analyze four years of data (2010, 2013, 2014, 2016) tracking residence and levels of cooperation elicited from a public goods game (PG), in Hadza hunter-gatherers of Tanzania. Data were collected from 56 camps, comprising 383 unique individuals, 137 of whom we have data for two or more years. Despite significant residential mixing, we observe a robust pattern of assortment necessary for cooperation to evolve: In every year, Hadza camps exhibit high between-camp and low within-camp variation in cooperation. We further consider the role of homophily in generating this assortment. We find little evidence that cooperative behavior within individuals is stable over time or that similarity in cooperation between dyads predicts their future cohabitation. Both sets of findings are inconsistent with homophilic models that assume stable cooperative and selfish types. Consistent with social norms, culture and reciprocity theories, the data suggest that the strongest predictor of an individual’s level of cooperation in any given year is the mean cooperation of their campmates in that year. These findings underscore the adaptive nature of human cooperation – particularly its responsiveness to social contexts – as a feature important in generating the assortment necessary for cooperation to evolve.

Perhaps no field of psychology is more strongly motivated and better equipped than evolutionary psychology to respond to the recent call for psychologists to expand their empirical base beyond WEIRD (Western Educated Industrialized Rich Democratic) samples. Evolutionary psychologists have historically focused their efforts on identifying species-specific psychological traits, for which evidence often hinged on the extent to which traits were generalizable across human groups. Now, a new generation of researchers is embracing cultural and environmental variation to test evolutionary hypotheses. Here we discuss how comparative research with diverse societies, while challenging, can help inform the complex nature of our species’ psychology and in doing so, we outline best theoretical and methodological practices as well as common pitfalls in cross-cultural investigations. We end with a recommendation for the use of publicly available databases for cataloging psychological variation across the world's many diverse populations. Because of rapid culture change and globalization, it is more important now than ever to document what we know about the world's cultures in ways that can be used by future researchers.

Our species is characterized by extraordinary biological success, which we owe, in large part, to our ability to cooperate. This cooperation extends beyond the pair bond to extended kin, affines, and even unrelated individuals. It has been suggested that one primary factor motivating such widespread cooperation in humans is the need to care for overlapping, energetically expensive offspring with long periods of development and dependency. For this reason, we situate the study of hunter-gatherer families and parenting within the larger context of human life history and cooperative networks. We argue that large, extended cooperative networks not only aid in meeting the demands of rearing hunter-gatherer children, but are also deeply rooted in our history. Keywords: hunter-gatherers; cooperation; social networks; cooperative breeding; families

The ratio between the length of the second and the length of the fourth digit (2D:4D) is sexually dimorphic such that males of many species possess a lower ratio than females, particularly in the right hand. Still, men and women often exhibit overlapping 2D:4D ranges and the ratio is highly variable between populations. In order to further explore populational variability, we chose to analyze 2D:4D in the Hadza, a population of hunter-gatherers living in Tanzania.Data were collected separately by two researchers over the course of three years (1998, 2001, 2006) from 152 adult participants (male: n = 76, female: n = 76). Independent samples t-tests were used to explore sex differences, paired samples t-tests were used to explore directional effects within each sex, and linear regression and one-way ANOVA were used to test possible age effects.In none of the years, or pooled (n = 152), did we find evidence that adult men have a lower 2D:4D than adult women. If anything, the data suggest that women in this population have a significantly lower right hand 2D:4D than men (P < 0.001, d = 0.57). In contrast, left hand 2D:4D did not exhibit a sex difference (P = 0.862, d = 0.03).These findings challenge the current view that lower 2D:4D in men is a uniform characteristic of our species. Cross-populational variance in 2D:4D may be related to known patterns of hormonal variation resulting from both genetic and environmental mechanisms, though this relationship merits further investigation.

Understanding the expansion of human sociality and cooperation beyond kith and kin remains an important evolutionary puzzle. There is likely a complex web of processes including institutions, norms, and practices that contributes to this phenomenon. Considerable evidence suggests that one such process involves certain components of religious systems that may have fostered the expansion of human cooperation in a variety of ways, including both certain forms of rituals and commitment to particular types of gods. Using an experimental economic game, our team specifically tested whether or not individually-held mental models of moralistic, punishing, and knowledgeable gods curb biases in favor of the self and the local community, and increase impartiality towards geographically distant anonymous co-religionists. Our sample includes 591 participants from eight diverse societies—Native Fijians who practice both Christianity and ancestor worship, the animist Hadza of Tanzania, Hindu Indo-Fijians, Hindu Mauritians, shamanist-Buddhist Tyvans of southern Siberia, traditional Inland and Christian Coastal Vanuatuans from Tanna, and Christian Brazilians from Pesqueiro. In this article, we present cross-cultural evidence that addresses this question and discuss the implications and limitations of our project. This volume also offers detailed, site-specific reports to provide further contextualization at the local level.

Since precise forecasting of the future is not possible, most of life’s decisions are made with uncertain outcomes. One important facet of uncertainty that is of particular interest to decision scientists is risk—the choice between an option that is less rewarding but more certain and an option that is less certain, but potentially more rewarding. Recent developments in both neuroscience and behavioral endocrinology have helped to reveal the biological mechanisms that support decision-making involving economic risk, and consequently, potential factors associated with individual differences in risk taking. This review is dedicated to surveying recent developments that link the hormone testosterone to economic risk taking. Like neuroeconomics, endocrinological approaches may provide a potentially powerful framework from which to understand decision-making and may help to make sense of a number of well-documented behavioral anomalies involving economic risk. Specifically, we suggest that testosterone functions to modulate risky behaviors in ways that appear to be adaptive. Still, more work is needed to understand the nature of the relationship between testosterone and risk in both sexes.

Previous research with hunter-gatherers has found that women perceive men with voices manipulated to be lower in pitch to be better hunters, and men perceive women with lower pitch to be better gatherers. Here, we test if actual voice pitch is associated with hunting and gathering reputations in men and women, respectively. We find that voice pitch does relate to foraging reputation in men, but not in women, with better hunters having a lower voice pitch. In addition, we find that the previously documented relationship between voice pitch and reproductive success no longer holds when controlling for hunting reputation, but hunting reputation remains a significant predictor of reproductive success when controlling for voice pitch. This raises the possibility that voice pitch is being selected for in hunter-gatherers because of the relationship between voice pitch and hunting reputation.

We study the willingness to compete against self and others in an experiment with over 650 participants, using a modified version of the Niederle and Vesterlund (2007) design. We show that introducing a possibility to self-compete, in addition to the standard other-competition option, increases the proportion of participants who compete by more than 60 percent, indicating that self-competition attracts many of those who would otherwise have stayed out of competitions altogether. This holds for both men and women. Moreover, men and women prefer self-competitions to other-competitions, especially when they have to select one of the two types of competitions. We also document that self-competitions are perceived as more controllable than other-competitions.

Despite numerous attempts to increase workplace equality, the near universal gender wage gap and underrepresentation of women in high status jobs persists in societies around the world. This persistence has led some researchers to speculate that psychological sex differences may be partly to blame. In particular, economists have begun to focus on sex differences in competitiveness as a possible cause. Here we test whether sex differences in competitiveness exist in a relatively isolated and evolutionarily relevant population of hunter-gatherers in Tanzania. In study 1 we examine sex differences in willingness to compete in a gender-neutral task in Hadza adults and children (N = 191). We find that when choosing between an individualistic payment scheme and a competitive payment scheme, boys and men are significantly more likely to compete than girls and women. We find no evidence that this sex difference varies with age. In study 2 (N = 88 and N = 70) we use both a female-centric and a male-centric task to explore sex differences in competitiveness in adults. While we find no sex difference in willingness to compete in the female-centric task, we find that men are more likely to compete in the male-centric task. While further work is needed, this study lends some support to the idea of a sex difference in willingness to compete among hunter-gatherers, but it also highlights the importance of the task type. The observation that a sizable proportion of male Hadza choose to compete in each of the tasks is discussed in light of the fact that hunter-gatherers are largely egalitarian and non-hierarchical.

Hunting is a characteristic feature of early human subsistence, and many theories of evolution have emphasized the role of hunting in hominization. Still today hunting ability continues to be selected for in extant foragers with better hunters experiencing greater reproductive success. Yet little is known about the traits that comprise a successful hunter traits that are presupposed to also be under selection. Two complementary empirical analyses were conducted to examine this question using data collected from Hadza hunter–gatherers in Tanzania. First, data on upper-body strength, running speed, target precision and visual and auditory acuity were collected to examine the traits that predict hunting reputation in men. Second, interview data were collected from Hadza informants regarding the traits they deem important for hunting. Results from the first study implicate upper-body strength as the strongest and most consistent predictor of men's hunting reputation. Hadza conventional wisdom also accord with these findings. Although informants stressed the importance of non-physical traits, such as “intelligence” and “heart”, strong arms were cited as the most important physical trait for hunting. Finally, men with stronger upper-bodies experienced greater reproductive success, a result that is largely mediated by hunting reputation. These findings suggest that selection for hunting ability may have acted on men's upper-bodies. Nevertheless, the importance of effort on strength and hunting success cannot be dismissed. This is also discussed.

A considerable body of research cross-culturally examines the evolution of religious traditions, beliefs and behaviors. The bulk of this research, however, draws from coded qualitative ethnographies rather than from standardized methods specifically designed to measure religious beliefs and behaviors. Psychological data sets that examine religious thought and behavior in controlled conditions tend to be disproportionately sampled from student populations. Some cross-national databases employ standardized methods at the individual level, but are primarily focused on fully market integrated, state-level societies. The Evolution of Religion and Morality Project sought to generate a data set that systematically probed individual level measures sampling across a wider range of human populations. The set includes data from behavioral economic experiments and detailed surveys of demographics, religious beliefs and practices, material security, and intergroup perceptions. This paper describes the methods and variables, briefly introduces the sites and sampling techniques, notes inconsistencies across sites, and provides some basic reporting for the data set.

Author(s): Bryant, GA; Fessler, DMT; Fusaroli, R; Clint, E; Aaroe, L; Apicella, CL; Petersen, MB; Bickham, ST; Bolyanatz, A; Chavez, B; Smet, DD; Diaz, C; Faněoviěova, J; Fux, M; Giraldo-Perez, PP; Hu, A; Kamble, SV; Kameda, T; Li, NP; Luberti, FR; Prokop, P; Quintelier, K; Scelza, BA; Shin, HJ; Soler, M; Stieger, S; Toyokawa, W; Van den Hende, EA; Viciana-Asensio, H; Yildizhan, SE; Yong, JC; Yuditha, T; Zhou, Y

The authors note that Table 1 appeared incorrectly. The corrected table appears below. (Table Presented).

In many primates, including humans, the vocalizations of males and females differ dramatically, with male vocalizations and vocal anatomy often seeming to exaggerate apparent body size. These traits may be favoured by sexual selection because low-frequency male vocalizations intimidate rivals and/or attract females, but this hypothesis has not been systematically tested across primates, nor is it clear why competitors and potential mates should attend to vocalization frequencies. Here we show across anthropoids that sexual dimorphism in fundamental frequency ( F 0 ) increased during evolutionary transitions towards polygyny, and decreased during transitions towards monogamy. Surprisingly, humans exhibit greater F 0 sexual dimorphism than any other ape. We also show that low- F 0 vocalizations predict perceptions of men's dominance and attractiveness, and predict hormone profiles (low cortisol and high testosterone) related to immune function. These results suggest that low male F 0 signals condition to competitors and mates, and evolved in male anthropoids in response to the intensity of mating competition.

Many studies show agreement within and between populations and cultures for general judgments of facial attractiveness. Studies that have examined the attractiveness of specific traits have also highlighted cross-cultural differences for factors such as symmetry, averageness, and masculinity. One trait that should be preferred across cultures is heterozygosity. Indeed, several studies suggest that mixed ethnicity, in terms of appearing to possess a mixture of traits from different human population groups, may be found attractive, which could reflect preferences for heterozygosity. We examined preferences for manipulated face shape associated with different populations in both Europeans (Britain) and Africans (Guinea-Bissau). We found that mixed-ethnicity face shapes were more attractive than enhanced single-ethnicity face shape across both populations. These results are consistent with evolutionary theories suggesting individuals should prefer heterozygosity in partners because facial cues to mixed-ethnicity are likely to indicate diverse genes compared to cues that indicate a face belongs to a single particular culture or population.

In this study, we investigate the association between a number of hormonal variables (circulating testosterone, facial masculinity, 2D:4D digit ratio, and cortisol) and competitiveness in a sample of 93 men aged 18-23. Competitiveness is measured by self-selection into a competitive setting versus a piece-rate scheme. We find no robust correlations between any of the hormonal variables and competiveness, though there are some suggestive patterns in the data which merit further exploration.

A robust positive correlation between height and intelligence, as measured by IQ tests, has been established in the literature. This paper makes several contributions toward establishing the causes of this association. First, we extend the standard bivariate ACE model to account for assortative mating. The more general theoretical framework provides several key insights, including formulas to decompose a cross-trait genetic correlation into components attributable to assortative mating and pleiotropy and to decompose a cross-trait within-family correlation. Second, we use a large dataset of male twins drawn from Swedish conscription records and examine how well genetic and environmental factors explain the association between (i) height and intelligence and (ii) height and military aptitude, a professional psychogologist’s assessment of a conscript’s ability to deal with wartime stress. For both traits, we find suggestive evidence of a shared genetic architecture with height, but we demonstrate that point estimates are very sensitive to assumed degrees of assortative mating. Third, we report a significant within-family correlation between height and intelligence \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\hat{\rho}=0.10),$$\end{document} suggesting that pleiotropy might be at play.

To test the relationship between androgen exposure, dopaminergic reward and sensation-seeking, we compared variation in salivary testosterone (T), 2D:4D digit ratio, facial masculinity, Zuckerman's sensation-seeking scale (SSS) and the D4 dopamine receptor (DRD4) genes from 98 young men, between the ages of 18 and 23 years. In univariate analyses, both salivary T and facial masculinity were significantly correlated with the SSS boredom susceptibility subscale, while the presence of the 7-repeat allele (7R+) in the dopamine receptor D4 gene was associated with the SSS thrill and adventure-seeking and overall sensation-seeking. Neither left nor right 2D:4D digit ratio was associated with any sensation-seeking scale. In multivariate models, salivary T and facial masculinity were significant predictors of SSS boredom susceptibility, while 7R+ was a significant predictor of SSS thrill and adventure-seeking. For overall SSS, both 7R+ and salivary T were significant predictors. There was no significant interaction of 7R+ and androgen exposure for SSS or any of the SSS subscales. These results add to earlier reports of an association between T and sensation-seeking. In addition, our results also indicate that genetic variation in DRD4 is independently associated with SSS sensation-seeking.

Individuals exhibit substantial heterogeneity in financial risk aversion. Recent work on twins demonstrated that some variation is influenced by individual heritable differences. Despite this, there has been no study investigating possible genetic loci associated with financial risk taking in healthy individuals. Here, we examined whether there is an association between financial risk preferences, elicited experimentally in a game with real monetary payoffs, and the presence of the 7-repeat allele (7R+) in the dopamine receptor D4 gene as well as the presence of the A1 allele (A1+) in the dopamine receptor D2 gene in 94 young men. Although we found no association between the A1

Many human behaviors, from mating to food acquisition and aggressiveness, entail some degree of risk. Testosterone, a steroid hormone, has been implicated in a wide range of such behaviors in men. However, little is known about the specific relationship between testosterone and risk preferences. In this article, we explore the relationship between prenatal and pubertal testosterone exposure, current testosterone, and financial risk preferences in men. Using a sample of 98 men, we find that risk-taking in an investment game with potential for real monetary payoffs correlates positively with salivary testosterone levels and facial masculinity, with the latter being a proxy of pubertal hormone exposure. 2D:4D, which has been proposed as a proxy for prenatal hormone exposure, did not correlate significantly with risk preferences. Although this is a study of association, the results may shed light on biological determinants of risk preferences.

A contribution to a special issue on Hormones and Human Competition. The effect of postural power displays (i.e. power poses) on hormone levels and decision-making has recently been challenged. While Carney et al. (2010) found that holding brief postural displays of power leads to increased testosterone, decreased cortisol and greater economic risk taking, this failed to replicate in a recent high-powered study (Ranehill et al. 2015). It has been put forward that subtle differences in social context may account for the differences in results. Power displays naturally occur within the context of competitions, as do changes in hormones, and researchers have yet to examine the effects of poses within this ecologically relevant context. Using a large sample of 247 male participants, natural winners and losers of a physical competition were randomly assigned to hold a low, neutral or high-power postural display. We found no main effect of pose type on testosterone, cortisol, risk or feelings of power. Winners assigned to a high-power pose had a relative, albeit small, rise in testosterone compared to winners who held neutral or low-power poses. For losers, we found little evidence that high-power poses lead to increased testosterone relative to those holding neutral or low-powered poses. If anything, the reverse was observed – losers had a reduction in testosterone after holding high-power poses. To the extent that changes in testosterone modulate social behaviors adaptively, it is possible that the relative reduction in testosterone observed in losers taking high-powered poses is designed to inhibit further “winner-like” behavior that could result in continued defeat and harm. Still, effects were small, multiple comparisons were made, and the results ran counter to our predictions. We thus treat these conclusions as preliminary.

Since the origins of agriculture, the scale of human cooperation and societal complexity has dramatically expanded. This fact challenges standard evolutionary explanations of prosociality because well-studied mechanisms of cooperation based on genetic relatedness, reciprocity and partner choice falter as people increasingly engage in fleeting transactions with genetically unrelated strangers in large anonymous groups. To explain this rapid expansion of prosociality, researchers have proposed several mechanisms. Here we focus on one key hypothesis: cognitive representations of gods as increasingly knowledgeable and punitive, and who sanction violators of interpersonal social norms, foster and sustain the expansion of cooperation, trust and fairness towards co-religionist strangers. We tested this hypothesis using extensive ethnographic interviews and two behavioural games designed to measure impartial rule-following among people (n = 591, observations = 35,400) from eight diverse communities from around the world: (1) inland Tanna, Vanuatu; (2) coastal Tanna, Vanuatu; (3) Yasawa, Fiji; (4) Lovu, Fiji; (5) Pesqueiro, Brazil; (6) Pointe aux Piments, Mauritius; (7) the Tyva Republic (Siberia), Russia; and (8) Hadzaland, Tanzania. Participants reported adherence to a wide array of world religious traditions including Christianity, Hinduism and Buddhism, as well as notably diverse local traditions, including animism and ancestor worship. Holding a range of relevant variables constant, the higher participants rated their moralistic gods as punitive and knowledgeable about human thoughts and actions, the more coins they allocated to geographically distant co-religionist strangers relative to both themselves and local co-religionists. Our results support the hypothesis that beliefs in moralistic, punitive and knowing gods increase impartial behaviour towards distant co-religionists, and therefore can contribute to the expansion of prosociality.

Average faces possess traits that are common to a population. Preferences for averageness have been found in several types of study of both real and computer-manipulated faces. Such preferences have been proposed to be biologically based and thus should be found across human populations, though cross-cultural evidence to date has been limited. In this study we examined preferences for averageness in both the West and in an isolated hunter-gatherer society, the Hadza of Northern Tanzania in Africa. We show that averageness is generally preferred across faces and cultures, but there were no significant preferences for averageness in European faces by Hadza judges. The different visual experience of the two cultures may explain the differences in preferences. While Westerners have visual experience of both European and African faces, the Hadza are limited in their experience of European faces, potentially leading to a lack of preference for averageness in this group because of the lack of a representation of the ‘norm’ of European faces.