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.

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.

Religious diversity has had profound consequences in human history, but the dynamics of how it evolves remain unclear. One unresolved question is the extent to which religious denominations accumulate gradually or are generated in rapid bursts associated with specific historical events. Anecdotal evidence tends to favour the second view, but quantitative evidence on a global scale is lacking. Phylogenetic methods that treat religious denominations as evolving lineages can help to resolve this question. Here we apply computational phylogenetic methods to a purpose-built data set documenting 291 religious denominations and their genealogical relationships to derive dated phylogenies of three families of world religions – Indo-Iranian, Islamic, and Judeo-Christian. We model the birth of new denominations along the branches of these phylogenies, test for shifts in the birth rate, and draw tentative links between the shifts we find and religious history. We find evidence for birth rate shifts in the Islamic and Judeo-Christian families, corresponding to at least three separate events that have shaped global religious diversity.

Humans often participate in physically harmful and demanding rituals with no apparent material benefits. Although such behaviours have traditionally been explained using the lens of costly signalling theory, we question whether the canonical theory can be applied to the case of human cooperative signals and introduce a modification of this theory based on differential benefit estimation. We propose that along with cooperative benefits, committed members also believe in supernaturally induced benefits, which motivate participation in extreme rituals and stabilize their effects on cooperative assortment. Using Thaipusam Kavadi as a prototypical costly ritual, Tamil (ingroup) and Christian (outgroup) participants in Mauritius (N = 369) assessed the cost and benefits of Kavadi participation or hiking. We found that ingroup participants estimated material costs as larger than outgroups, physical costs as lower, and benefits as larger. These findings suggest that estimated costs may vary by modality and cultural expectations (e.g. Kavadi participants are not supposed to display pain), while supernaturally induced benefits were consistently reported as larger by ingroups compared to outgroups. We conclude that differential estimation of ritual benefits, not costs, are key to the persistence of extreme rituals and their function in the assortment of committed members, underscoring the role of differential estimation in the cognitive computation of signal utility.

We assess the proposition that intergroup conflict (IGC) in non-human primates offers a useful comparison for studies of human IGC and its links to parochial altruism and prosociality. That is, for non-linguistic animals, social network integration and maternal influence promote juvenile engagement in IGC and can serve as the initial grounding for sociocultural processes that drive human cooperation. Using longitudinal data from three cohorts of non-adult vervet monkeys (Chlorocebus pygerythrus), we show that non-adults are sensitive to personal (age) and situational risk (participant numbers). The frequency and intensity of participation, although modulated by rank and temperament, both mirrors maternal participation and reflects non-adult centrality in the grooming network. The possibility of social induction is corroborated by the distribution of grooming during IGC, with non-adults being more likely to be groomed if they were female, higher-ranking and participants themselves. Mothers were more likely to groom younger offspring participants of either sex, whereas other adults targeted higher-ranking female participants. Although we caution against a facile alignment of these outcomes to human culturally mediated induction, there is merit in considering how the embodied act of participation and the resultant social give-and-take might serve as the basis for a unified comparative investigation of prosociality.

Humans are characterised as cooperative breeders, as not only the parents but also other members of the social group take part in raising offspring. The individuals who invest most in childrearing are usually the more closely related individuals. However, most studies have concentrated on close kin and the effects of more distant kin remain unknown. Here, we investigated the associations of child mortality (<5years, n=32,000 children) with the presence of 36 different types of relatives, divided by lineage and sex, in a historical Finnish population. We found that the presence and greater number of several paternal relatives were associated with an increase in child mortality and many of these associations were seen among the wealthiest families, due to inheritance practices and shared resources. The presence of the maternal grandmother was associated with a decrease in child mortality and the most among poorer families, who probably needed the grandmother's contribution more than the wealthy. Our results bring new insights into the importance of kin and suggest that relatives can provide support or other resources but also compete for limited resources and care. The results give a broader perspective of human family life and increase understanding of the evolution of cooperative breeding.

Individuals who experience divorce in childhood are more likely to divorce themselves as adults. Notably, the magnitude of the intergenerational divorce transmission is stronger for groups among whom divorce is rare. This transmission may reflect differences in mating strategies passed from parent to child, or differences in cultural norms between groups. Sociologists and demographers have struggled to disentangle socioeconomic and cultural factors, because groups that are less wealthy also tend to have higher divorce rates. We use data from Finland, where two native ethnolinguistic groups with comparable socioeconomic characteristics – but different divorce risks – live side by side: Swedish-speakers and Finnish-speakers. Using register data on the entire Finnish population (N = 554,337 couples 1987–2020), we examine separation risk as a function of parental divorce. Data suggest that the intergenerational transmission is greater among Swedish-speakers, who have an overall lower separation rate. Group differences in separation risk persist even after controlling for socioeconomic factors and each partner’s experience of parental divorce. Notably, Finnish-speaking couples who reside in Swedish-dominated areas have both somewhat lower separation risk, and higher intergenerational transmission than their peers in Finnish-dominated areas. These results point to a cultural transmission of separation, beyond strong socioeconomic factors.

Abstract We recently reported that cultural group membership may be a predictor of the likelihood that an individual will detect a faked accent in a recording. Here, we present follow-up data to our original study using a larger data set comprised of responses from the across the world. Our findings are in line with our previous work and suggest that native listeners perform better at this task than do non-native listeners overall, although with some between-group variation. We discuss our findings within the context of signals of trustworthiness and suggest future avenues of research.

Derived from the disease-avoidance model is the hypothesis that people may direct negative cognitive and behavioural responses towards individuals with physical disfiguring conditions, including physical disabilities. According to the behavioral immune system, physical disability—a non-contagious physical disfigurement—may falsely activate cognitive disease-avoidance processes, resulting in prejudicial or negative responses toward individuals with physical disabilities. For the first time this hypothesis is put to the test by investigating whether ratings of attractiveness and comfort for a social interaction vary systematically with physical disability (Studies 1 and 2). In addition, we tested whether these ratings were associated with individual differences in pathogen disgust and perceived vulnerability to disease. In Study 3 we overcame possible methodological limitations by employing a virtual reality (VR) environment. A fourth study was conducted to extend the first two studies by using a more diverse set of avatars. Results from Studies 1 and 2 indicated that disability did not significantly impact comfort ratings for social interactions, although non-disabled stimuli were rated as more attractive. However, Study 3 showed that in a VR environment, participants preferred closer proximity to non-disabled avatars over disabled ones, a preference not mitigated by the presence of prosthetics. Study 4 replicated these findings with varied 2D avatars, showing that disability significantly affected both comfort and attractiveness ratings, with non-disabled avatars rated highest, followed by those with prosthetics, and finally disabled avatars. Despite these findings, the expected relationship between comfort ratings and individual differences in pathogen disgust or perceived infectability did not emerge, challenging the behavioural immune system proposal. The discomfort associated with physical disability may be more related to social stigma or preconceived notions than to an innate disease-avoidance response.

How does information infrastructure shape long-term cultural evolution? Using over four centuries of professional game records from the game of Go, this study explores how strategic dynamics in opening moves reflect historical shifts in the ‘infostructure’ of skilled Go players. Drawing from recent work on how population size, AI, and information technology affect cultural evolution and innovation dynamics, I analyze over 118,000 games using measures of cultural diversity, divergence, and player network composition. The results show distinct eras of collective innovation and homogenization, including an early 20th-century explosion of novel opening strategies, a Cold-War-era die-off, and a recent increase in evolutionary tempo with the arrival of the internet and superhuman AI programmes like AlphaGo. Player population size shows an inverse-U relationship with opening move diversity, and a recent decline in strategic diversity has accompanied a shift in the player network, from many small subgroups to a few large ones. Surprisingly, the influence of AI has produced only a modest, short-lived disruption in the distribution of opening moves, suggesting convergence between humans and AI and incremental rather than revolutionary cultural change.