The prevalence of religious beliefs and practices is puzzling from an evolutionary perspective, but previous research has suggested that religious traditions may provide cooperative benefits and improve well-being. Seemingly in contrast to this claim are worldwide secularization trends in which people disaffiliate from religions and abandon belief in God. Theorists have suggested that diminished pressures on cooperation and well-being no longer motivate individuals to seek religious benefits and pay the associated participation costs. We investigate this claim using the National Study of Youth and Religion dataset, which tracks the development of religiosity among US Christians from adolescence to young adulthood (n = 3,370). Using a lagged panel design, we found that material security in Wave 1 (early adolescence) predicts a decrease in belief in God in Wave 4 (young adulthood), although this association is rather small. This result provides some support for the hypothesis that participation in religious traditions is associated with living in an insecure socio-ecology, where religious systems may still confer benefits on their members; yet it is not the only driver of secularization. We conclude with a call for further research using more nuanced measures and larger sample sizes to provide deeper insights into the potentially adaptive nature of cultural systems.

The distinct size and shape of breasts in women is a uniquely human trait. This trait has no conclusive explanation as it is not a requirement for milk production. Additionally, breasts are already enlarged at puberty, which is usually long before the first pregnancy. We hypothesized that the perennially enlarged human breasts were potentially developed to support infant’s thermal balance by providing increased warming surface in skin-to-skin contact.

To test the hypothesis, we measured breast surface temperature to explore their heating capacity and resilience to temperature changes in an environmental conditions laboratory. Volunteers, divided in groups of nursing women, non-nursing women, and men, were exposed to three temperatures: 32°C, 27°C, and 18°C. The exposure time in each temperature was 20 min. The changes in breast surface temperature were recorded by thermal imaging camera. Data were analysed using Kruskal–Wallis tests. Breastfeeding women had overall higher mammary surface temperature compared to other groups. Furthermore, nursing women had distinct resilience against cooling environment: they lost the average of 2.5°C of their mammary surface temperature, whereas other study groups lost 4.3°C and 4.7°C of surface temperature, respectively. This proof-of -concept study clearly indicated the potential of the nursing women’s breasts to support infant’s thermal balance.

The origins and correlates of war are historically contentious in anthropology, with researchers divided over its relationship to the development of agriculture, sedentism, and centralized states. Although this research tends not to focus on norms of wartime conduct, its arguments can be extended to how the levels and forms of violence directed at enemies vary with social complexity. For this study, variables on social complexity and warfare were coded from ethnographic and historical sources into a cross-cultural data set of 73 societies. The likelihood of different individuals who were enemies of the focal society being targeted or killed during war was tested for relationships with measures of social complexity and violent conquest of external populations. The results of the analyses provided little to no evidence for increased or decreased indiscriminate violence with social complexity (as measured by population size, governance levels, and centralization), or for a strong relationship with formal military structures and political/territorial expansion. A multidisciplinary literature review of how wartime violence relates to social structures is also presented. Interpretations, limitations, and future directions are discussed in the context of comparative cultural databases and their applications to cultural evolution research.

Researchers have long speculated about the evolutionary benefits of religiosity. One explanation for the evolution of religious ritual is that rituals signal commitment to co-religionists. As a major domain of prosocial behaviour, alloparental care – or care directed at children by non-parents – is a plausible benefit of religious signalling. The religious alloparenting hypothesis posits that parents who signal religious commitment receive greater alloparental support. Prior research on religiosity, cooperation, and allocare tends to treat individuals as isolated units, despite the inherent collective nature of religious cooperation. Here, we address this limitation in a survey-based study of 710 parents in rural Bangladesh. Instead of focusing only on mothers, we consider the interplay between both mothers and fathers in eliciting allocare, and leverage variation in the covertness of religious rituals to test a key mechanistic assumption linking religious ritual with cooperation. We find that parents who practice religious rituals more frequently receive greater alloparental support from co-religionists. This effect is moderated by parent gender, as well as variation in the visibility of religious rituals. Women’s private practices positively affect only those alloparents with whom they share a household, whereas men’s public practices positively affect alloparents more broadly.

Women’s mental health is commonly regarded as worse than that of men across most cultures and countries, although the pronounced female disparity for affective disorders, particularly depression and anxiety, is reversed for other mental conditions such as addiction, alcoholism, or autism. Here we probe this puzzle within a life-history adaptationist framework, focusing on the high prevalence of mood disorders among women with the goal to evaluate their adaptive rather than pathological qualities. First, we characterize gender disparities in mental health, particularly mood disorders among women, and review their phenomenology. Then we survey known risks for mood disorder on cultural, ecological, experiential, and physical/physiological dimensions. Next we consider adaptationist explanations for depression, and map women’s life history in non-industrial societies, plotting resources, demands, and selection pressures. Thence we turn to how life-course selection pressures and female adaptive responses to them operate and intersect, illustrated by an example of low birthweight effects. Affective disorders vary in phenotype and prevalence within and across societies and through time, arising from an array of context-sensitive cost–benefit trade-offs for females that operate from birth onwards. Available evidence suggests that the general preponderance of mood disorder among females is adaptive overall albeit via multiple pathways.

Human handedness results from the interplay of genetic and cultural influences. A gene-culture co-evolutionary model for handedness was introduced by Laland et al. (1995), and this study generalizes that model and the related analysis. We address ambiguities in the original methodology, particularly regarding maximum-likelihood estimation, and incorporate sex differences in cultural transmission. By fitting this extended framework to existing familial and twin datasets, we demonstrate that accounting for criterion shifts significantly improves model fit and parameter estimation accuracy. We find stronger maternal than paternal effects on handedness, with daughters exhibiting greater sensitivity to these effects than sons. We provide an open-source Python implementation of the model, which is a robust platform for comparing gene-culture models and applying them to diverse datasets.

Mid-last century, controversy existed around the question whether non-human great apes have culture. To a large degree, this is no longer controversial – apes have their own cultures. However, there remains controversy around how to best study ape culture, given the varying and often dichotomised contributions from captive and field-ape research. Here, we present a historical summary of the ape culture wars since their inception and how this has evolved over time. We then focus on debates surrounding wild versus captive-ape research with an emphasis on culture, detailing major arguments arising from both research domains. Throughout, we critically deconstruct these arguments, illustrating the nuance behind these critiques, while highlighting their assumptions, overgeneralising statements and potential constraints. We further provide potential solutions to help alleviate the issues we describe, when possible. We also offer a metacritique of ape culture research for its scientific and political impact, irrespective of one’s expertise. In closing, we summarise concrete recommendations for a richer and more holistic understanding of ape, and human, culture.

Research focusing on first impression formation based on facial stimuli lacks a conclusion on whether there is a cross-cultural agreement and how deeply it has proliferated across distant populations. Social media may play an important role in the level of cross-cultural agreement as they provide us with overwhelming numbers of visual stimuli, including faces. Sharing social media aesthetics, their users may utilise facial cues congruently. We asked participants from seven distant, ethnically variable countries from five continents to rate facial attractiveness, trustworthiness and dominance of a single ethnically invariant facial sample (N = 195, 106 women, M_Age = 23.23), also accounting for their self-reported social media use intensity and socioeconomic background. We expected the agreement between cultures to be better for participants who reported a higher intensity of social media use. Instead, we observed substantial cross-cultural agreement, especially for attractiveness and trustworthiness, regardless of the self-reported social media use intensity. However, the samples of participants from similar cultural backgrounds (same countries) agreed more. We also see substantial agreement in facial cue utilisation. In line with previous research, the distinctiveness of facial shape affects perceived attractiveness congruently across cultures. Despite the relatively small age range, age positively affects ascribed dominance.

Patterns of social organisation and gender differentiation in past societies are difficult to reconstruct from material culture data alone, are prone to modern interpretation biases, and often remain subjects of controversy. An important aspect of social organisation is patterns of post-marital residence, for example, matrilocality and patrilocality. To date, archaeological studies have recognised mostly patrilocal communities, with rare contested exceptions that were considered ‘outliers’ to the established rule of patrilocality. The advent of ancient DNA analysis has made it possible to evaluate past social structures from a genetic perspective as well, with the majority of ancient DNA studies identifying patrilocal communities and highlighting genetic patriline connections. Recently, three studies reported genetic evidence for matrilocality and genetic matriline connections across broad geographical and temporal scales. Here, we draw on these three studies to explore past social organisation forms in light of new evidence and reconsider preconceptions that continue to endure over time.

Tooth wear constrains feeding efficiency, life history, and survival in mammals, yet its progression in wild populations remains poorly understood. We use high-resolution 3D analysis to quantify occlusal tissue loss over a 3-year period in the upper premolars and molars (P3-M3; n = 70) of wild baboons (Papio). Our sample includes olive baboons (P. anubis) and naturally occurring olive-hamadryas hybrids (P. anubis × P. hamadryas) from Awash National Park, Ethiopia. We calculate mean values for tooth types, visualize tissue loss across occlusal surfaces, and compare individuals by age, sex, and hybrid status. Molars lost tissue faster than premolars (molars: 0.13 mm3/mm2/year; premolars: 0.08 mm3/mm2/year), with the bulk of wear shifting from lingual to buccal cusps in older individuals. The rate of tissue loss did not increase with age, despite greater dentine exposure. There was no clear difference in wear patterns relating to sex or hybrid status, although subtle sex-related differences in P3 wear patterns were observed. These findings demonstrate the adaptive significance of gradual tissue loss in preserving dental function and establish comparative baselines for interpreting wear patterns in extinct primates, where dental remains often provide the primary record of diet and behaviour.

Indirect reciprocity is a reputation-based mechanism proposed to explain the evolution of human cooperation. Theoretical models demonstrated that the use of both first-order information (i.e., whether an evaluation target cooperated) and second-order information (i.e., the reputation of an interaction partner of the evaluation target) is critical for the evolution of cooperation. However, empirical findings on the use of second-order information have been mixed. Drawing upon the literature on group-bounded indirect reciprocity, we tested the hypothesis that individuals would be more sensitive to second-order information when evaluating in-group interactions, compared to when evaluating out-group interactions. We conducted a preregistered online experiment (N = 604), where we independently manipulated group membership (in-group vs. out-group), target behaviour (cooperation vs. defection), and recipient reputation (good vs. bad). We found that donors who defected against good recipients were rated more negatively than those who defected against bad recipients, indicating the use of second-order information. Partly consistently with our hypothesis, when individuals evaluated coopering donors, second-order information influenced reputation for in-group donor–recipient interactions more than for out-group donor–recipient interactions. Nevertheless, individuals readily used second-order information, whether or not they evaluated in-group or out-group donor–recipient interactions.

Life history theory seeks to understand how organisms distribute energy between physiological functions across the life course. A central assumption is that energy allocation involves ‘trade-offs’ between competing functions relating to defence, maintenance, reproduction, and growth. Constraints on human energy expenditure may produce trade-offs during energetic stress, affecting functions critical for homeostasis, survival, and reproduction. While there is some evidence for binary trade-offs between two functions in humans, no studies have tested physiological resource prioritisation across multiple functions under energetic constraint. This study empirically assessed multiple human life history trade-offs and the proximate biological mechanisms underpinning them. We recruited 147 ultra-endurance athletes (107 male, 40 female) participating in four environmentally diverse multiday ultramarathons and one multiweek ocean rowing event. The severe energetic demands of these competitions provide a valuable opportunity to provoke and observe detectable trade-offs. We found evidence of trade-offs across multiple functions. Specifically, investment in defence (as indexed by immune biomarkers) was broadly prioritised relative to investment in storage, reproduction and maintenance. Our results enhance current understanding of the role of phenotypic plasticity in human adaptability and have implications for athlete health and performance as well as the emerging discipline of evolutionary public health.

Explaining how cooperation evolves is a major research programme in the biological and social sciences. In this study, we tested evolutionary theories of human cooperation in a real-world social dilemma: joint liability microfinance, in which groups of borrowers must cooperate to successfully repay a shared loan. We used pre-registered Bayesian multilevel models to estimate meta-analytic associations between loan repayment and proxies of four evolutionary mechanisms proposed to support cooperation: relatedness, reciprocity, partner choice, and punishment. A systematic search of the microfinance literature yielded 73 effect estimates for 11 proxies of evolutionary mechanisms analysed in 11 separate meta-analyses. Punishment-based variables showed the strongest positive meta-analytic associations with loan repayment, with mixed results for other mechanisms. However, estimates varied widely in their certainty, with generally high levels of between-study heterogeneity. Our results provide some evidence for evolutionary mechanisms supporting cooperation in real-world contexts, but also indicate there are non-generalisable findings and/or reproducibility issues in the microfinance literature.

Learning is crucial for humans and other animals to acquire knowledge, enhancing survival and reproduction. In particular, individual and social learning allow populations to accumulate knowledge across generations. Here, we examine how stochasticity in the production and social acquisition of knowledge influences the evolution of learning schedules and cumulative knowledge. Using a mathematical model where learning is stochastic, we show that learning stochasticity enhances cumulative knowledge by generating variability in knowledge levels. This allows selection to enhance population knowledge: individuals who acquire more knowledge by chance are more likely to survive and reproduce, and therefore to transmit their knowledge to the next generation. As knowledge accumulates, social learning exemplars tend to possess more of it, favouring greater time investment in social learning. Because social learning provides access to substantially more knowledge when learning is stochastic, selection also favours the evolution of greater investment into learning, at the expense of a fecundity cost. Moreover, when knowledge enhances fecundity but not survival, learning stochasticity favours learning from parents rather than other adults, because learning stochasticity increases uncertainty about exemplar knowledge, making parenthood a cue for possessing fecundity-enhancing knowledge. Finally, when learning occurs predominantly from parents, learning stochasticity itself is favoured by selection.

Individual social identities indicate group affiliations and are typically associated with group-typical preferences, signals that indicate group membership, and the propensity to condition actions on the social signals of others, resulting in group-differentiated interaction norms. Past work modelling identity signalling and co-ordination has typically assumed that individuals belong to one of a discrete set of groups. Yet individuals can simultaneously belong to multiple groups, which may be nested within larger groupings. Here, we introduce the generalized Bach or Stravinsky game, a co-ordination game with ordered preferences, which allows us to construct a model that captures the overlapping and hierarchical nature of social identity. Our model unifies several prior results into a single framework, including results related to co-ordination, minority disadvantage, and cross-cultural competence. Our model also allows agents to express complex social identities through multidimensional signalling, which we use to explore a variety of complex group structures. Our consideration of intersectional identities exposes flaws in naive measures of group structure, illustrating how empirical studies may overlook some social identities if they do not consider the behaviours that those identities function to afford.

In this paper, we chart an emerging academic terrain: cultural evolution of the arts, which is a theory-driven exploration of artistic dynamics, often done with large datasets of music, literature, movies, paintings, or games. This field has grown at the intersection of cultural evolution theory and several academic fields: computational humanities, anthropology, network science, and others, and poses interesting challenges for each of them. What constitutes artistic transmission in the first place? Is it possible to find recurring patterns in artistic history – and how much data is needed for that? What makes the evolution of the arts different from the evolution of other forms of knowledge? We discuss all these problems in this paper. Additionally, we perform a bibliometric analysis of this field and explore a co-citation network of the works on artistic evolution. Finally, we highlight major challenges for this field in the future, as the arts are rapidly evolving in the digital age.

Current debates concerning the use of digital technology often focus on privacy, yet privacy attitudes and behaviour are remarkably under-theorized, and relatively little empirical research has investigated privacy beyond the realm of digital communications. Building on evolutionary scholarship on information exchange, we outline a theoretical model in which cultural concepts of privacy reflect the workings of evolved psychological mechanisms that aim to regulate others’ access to fitness-relevant information towards adaptive ends. Results of two initial U.S. vignette studies distributed via Prolific (n = 425, 120) support the core predictions of this model, suggesting that people may have implicit and unstated assumptions regarding how information spreads in social environments. Specifically, participants’ privacy evaluations were predicted by whether information was intentionally acquired, the extent to which information was transmitted, and an individual’s position in an information transfer event. Importantly, how information was acquired and the nature of its transmission constituted independent but interacting influences on privacy perceptions. Additionally, results suggest the location within shared social networks of the individual to whom information is transmitted is used as a proxy for the potential costs of dissemination.