Striking a balance between individual and social learning is one of the key capabilities that support adaptation under uncertainty. Although intergenerational transmission of information is ubiquitous, little is known about when and how newcomers switch from learning loyally from preceding models to exploring independently. Using a behavioural experiment, we investigated how social information available from a preceding demonstrator affects the timing of becoming independent and individual performance thereafter. Participants worked on a 30-armed bandit task for 100 trials. For the first 15 trials, participants simply observed the choices of a demonstrator who had accumulated more knowledge about the environment and passively received rewards from the demonstrator's choices. Thereafter, participants could switch to making independent choices at any time. We had three conditions differing in the social information available from the demonstrator: choice only, reward only or both. Results showed that both participants’ strategies about when to stop observational learning and their behavioural patterns after independence depended on the available social information. Participants generally failed to make the best use of previously observed social information in their subsequent independent choices, suggesting the importance of direct communication beyond passive observation for better intergenerational transmission under uncertainty. Implications for cultural evolution are discussed.

It is commonly argued that humans have generalised predispositions for within-group favouritism and between-group animus (i.e. that humans are parochially altruistic), leading to higher levels of internal conflict in societies with greater diversity. Other research, however, has questioned both the ubiquity of parochial altruism and the role of diversity per se in causing social discord. Here, we use ethnographic, social network and experimental economic game data to explore this topic in two multi-ethnic Colombian communities. We examine the extent to which Afrocolombian and Emberá residents express parochial altruism, finding appreciable variability between communities, and across individuals within communities. When present, parochial altruism appears to be driven by divergent perceptions of group-based economic need, not group identity per se. Our results suggest that diversity may be less likely to cause social discord than past work has suggested, as long as group-based inequalities in wealth, well-being and representation – that can destabilise positive inter-group relationships – are minimised.

Humans often learn preferentially from ingroup members who share a social identity affiliation, while ignoring or rejecting information when it comes from someone perceived to be from an outgroup. This sort of bias has well-known negative consequences – exacerbating cultural divides, polarization, and conflict – while reducing the information available to learners. Why does it persist? Using evolutionary simulations, we demonstrate that similarity-biased social learning (also called parochial social learning) is adaptive when (1) individual learning is error-prone and (2) sufficient diversity inhibits the efficacy of social learning that ignores identity signals, as long as (3) those signals are sufficiently reliable indicators of adaptive behaviour. We further show that our results are robust to considerations of other social learning strategies, focusing on conformist and pay-off-biased transmission. We conclude by discussing the consequences of our analyses for understanding diversity in the modern world.

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 (<5 years, 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.

We review the methods we developed to study female genital cutting in Sudan and sex-selective abortion in Armenia. These methods were untested at the time of our original research, and here we compare the distinct but overlapping approaches we used to validate our methods for each of the two countries. Additionally, we repeat a number of analyses, including those related to validation, with previously unpublished data from Sudan. All results replicate previous findings. Replicating previous results is encouraging, but we nonetheless argue that validation for Armenia is more convincing than for Sudan. Specifically, even if female genital cutting and the preferential abortion of females are equally sensitive as research topics, son bias is inherently easier to study than cutting because biological sex determination is a random process with no natural analogue in the case of cutting. This randomness provides a kind of cover for research participants who are son-biased but want to create the impression that they are not. This cover, in turn, allows the researcher to resolve any trade-off between methods that produce explicit granular data and methods that produce untraceable, highly aggregated data in favour of methods producing the explicit and granular.

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.

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.

With the objective of informing theoretical accounts of social learning and gendered conflict, we explore the role of prestige in the formation of men’s beliefs about gender in a semi-rural but fast urbanizing community in north-western Tanzania. Using focus groups and participant observation, we contrast the extent to which young men view elders and men from the neighbouring city as prestigious, and the beliefs they ascribe to each category. Elders were viewed as prestigious because of their age and position as preservers and teachers of societal norms. Their prestige was culturally mandated, as evidenced by customs bestowing respect. In contrast, only subcategories of city men were deemed prestigious dependent on individual achievement. Prestige was difficult to distinguish from dominance, as both elders and city men can exert penalties on those with differing views. Elders were viewed as mostly, but not always, unsupportive of women’s empowerment, whereas city men were viewed as mostly, but not always, supportive of women’s empowerment. We conclude that urbanization shifts the distribution of prestige, exposing individuals to novel sources of social influence. However, future studies should be wary not to oversimplify elders as upholders of patriarchal beliefs and city men as universally supportive of women’s empowerment.

The suffixing bias (the tendency to exploit suffixes more often than prefixes to express grammatical meanings) in languages was identified a century ago, yet we still lack a clear account for why it emerged, namely, whether the bias emerged because general cognitive mechanisms shape languages to be more easily processed by available cognitive machinery, or if the bias is speech-specific and is determined by domain-specific mechanisms. We used statistical learning (SL) experiments to compare processing of suffixed and prefixed sequences on linguistic and non-linguistic material. SL is not speech-specific, and we observed the suffixing preference only on linguistic material, suggesting its language-specific origin. Moreover, morphological properties of native languages (existence of grammatical prefixes) modulate suffixing preferences in SL experiments only on linguistic material, suggesting limited cross-domain transfer.

The parallel trails of footprints at Laetoli site G are important fossils for studying the characteristics of Australopithecus afarensis. However, the relationship between the trackmakers – i.e. whether it was that of an adult male–female pair or of parent–offspring – remains unclear. The footprints show that the two individuals walked side by side with a narrow and constant distance between them and synchronized their leg movements and step lengths (gait synchronization), although they had a large height difference. In this study, live camera videos were collected to obtain data on gait synchronization in Homo sapiens, the closest extant species to A. afarensis. The data showed that when two humans with a large height difference walked alongside each other, with (at least) one of the pair having their arm around the other’s shoulder or back, adult male–female pairs (couples) frequently synchronized their gait, but parent–offspring pairs did not, whereas both couples and parent–offspring seldom synchronized when they walked side by side without connection or with handholding. Two individuals only maintained a narrow and constant distance like that between the Laetoli footprints when they walked with an arm-around connection. Therefore, assuming that A. afarensis had the same gait synchronization tendency as H. sapiens, the trackmakers were more likely to be an adult male–female pair than a parent–offspring one.

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.

Perception studies describe numerous discrete morphological facial features as important to judgements of various characteristics. Interestingly, little is known about whether people actually direct their visual attention to these features and how specific contexts or sex affect this attention. We, therefore, examined visual attention to faces in the context of intersexual (opposite-sex assessment of attractiveness) and intrasexual (same-sex assessment of dominance) selection.

In total, 93 women and 33 men rated 80 high-resolution facial photographs of men and women while their gaze was recorded using eye-tracking. To explore patterns of raters’ attention to faces and specific facial features, we used the number of fixations, fixation duration, and visit duration as visual attention measures.

Women directed more visual attention towards the faces of potential partners (more fixations) than potential rivals, and men had longer fixation duration when assessing potential partners than rivals. Facial features that acquired the most visual attention across contexts and sexes were the eyes, nose, and mouth, but small differences between the sexes and contexts in visual attention were found for other facial regions suggested by previous perception studies, such as the chin and the cheeks indicating their importance in specific judgements.

Survey results have shown that the traits women seek in a partner are different from the traits parents seek in a son-in-law. These differences have been attributed to parent–offspring conflict, where parents prefer mates for their offspring who provide benefits to the entire family group, but adult women prefer traits in a potential partner that indicate heritable fitness (e.g. creativity, exciting personality). We compare the characteristics of husbands of women in self-choice and arranged marriages using data from the longitudinal Indonesia Family Life Survey (IFLS) which surveyed families between 1993 and 2015. Results show that the husbands of women in arranged marriages had lower levels of completed education than those from self-choice marriages, counter to predictions. There were no significant differences in the husband’s wealth prior to marriage or the proportion of couples who were of the same religion. An examination of personality traits showed little difference based on arranged marriage status. The only prediction that had significant support was that couples in arranged marriages were more likely to share an ethnic background than couples in self-choice marriages. These results suggest that the characteristics of husbands vary little by arranged versus self-choice marriage status, contrary to previous survey findings.

Concerns have been raised that an excess of men leads to societal violence, including violence against women, although recent evidence has challenged this view. One area that remains untested is honour killings, a type of femicide perpetrated by unrelated family members, such as intimate partners, and related family members, such as parents and siblings. Using a novel data set of media reports of honour killings from Pakistan we test whether the sex ratio is associated with femicide. To address reporting bias, we implement two case-control studies. The first compares media reports of honour killings to male suicides. The second compares honour killings perpetrated by unrelated individuals to those perpetrated by kin. We find evidence that honour killings perpetrated by unrelated individuals are higher in male-biased areas compared to those perpetrated by kin. Honour killings of women by kin therefore appear less sensitive to the sex ratio. Results align with sexual selection theory, suggesting more male competition may lead to more violence. We also find weak evidence that male-biased areas report more male suicides than honour killings. However, we caution against drawing causal conclusions due to potential confounding variables, particularly economic deprivation. This highlights the challenges of studying sensitive topics quantitatively.

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.

We present a comprehensive analysis of the rise of fictions across human narratives, using large-scale datasets that collectively span over 65,000 works across various media (movies, literary works), cultures (over 30 countries, Western and non-Western), and time periods (2000 BCE to 2020 CE). We measured fictiveness – defined as the degree of departure from reality – across three narrative dimensions: protagonists, events, and settings. We used automatic annotations from large language models (LLMs) to systematically score fictiveness and ensured the robustness and validity of our measure, specifically by demonstrating predictable variations in fictiveness across different genres, in all media. Statistical analyses of the changes in fictiveness over time revealed a steady increase, culminating in the 20th and 21st centuries, across all narrative forms. Remarkably, this trend is also evident in our data spanning ancient times: fictiveness increased gradually in narratives dating back as far as 2000 BCE, with notable peaks of fictiveness during affluent periods such as the heights of the Roman Empire, the Tang Dynasty, and the European Renaissance. We explore potential psychological explanations for the rise in fictiveness, including changing audience preferences driven by ecological and social changes.