Humans tend to be prosocial towards in-group members, but often hostile towards out-group members. In line with ethology and evolutionary psychology, this study develops the concept of Durkheimian learning, meaning that groups actively integrate individuals by cultural transmission of behavioral norms. Yet humans might have genetically evolved predispositions for indoctrinability and constrained learning of what is adaptive for self-interested individuals living in groups. In-group prosociality might have coevolved with tendencies towards out-group rejection. The mechanism behind this outcome might have been cultural-group selection in combination with gene-culture co-evolution. The feasibility of the argument will be illustrated by two simulation experiments of a selfish-teamwork game. Inspired by the Price equation of multilevel selection, the simulations combine fuzzy group-boundaries and between-group competition with cooperative behavior and intergenerational cultural transmission of prosocial behavior within groups. Results show that group boundaries, e.g. due to cultural markers, can explain the evolution of cooperative behavior. However, efficient Durkheimian learning and intergroup competition might have accelerated its expansion, despite of considerable levels of between-group migration. This insight will be discussed in the light of recent arguments from cultural evolutionary psychology.
Humans tend to be prosocial towards in-group members, but often hostile towards out-group members. In line with ethology and evolutionary psychology, this study develops the concept of Durkheimian learning, meaning that groups actively integrate individuals by cultural transmission of behavioral norms. Yet humans might have genetically evolved predispositions for indoctrinability and constrained learning of what is adaptive for self-interested individuals living in groups. In-group prosociality might have coevolved with tendencies towards out-group rejection. The mechanism behind this outcome might have been cultural-group selection in combination with gene-culture co-evolution. The feasibility of the argument will be illustrated by two simulation experiments of a selfish-teamwork game. Inspired by the Price equation of multilevel selection, the simulations combine fuzzy group-boundaries and between-group competition with cooperative behavior and intergenerational cultural transmission of prosocial behavior within groups. Results show that group boundaries, e.g. due to cultural markers, can explain the evolution of cooperative behavior. However, efficient Durkheimian learning and intergroup competition might have accelerated its expansion, despite of considerable levels of between-group migration. This insight will be discussed in the light of recent arguments from cultural evolutionary psychology.
The relationship between facial expressions and facial shape is surprisingly understudied. We use facial videos and photographs, along with others' judgements, to investigate the interplay among facial morphology, dynamics, and perception. Facial expressions were quantified through Action Units (AUs) using the Facial Action Coding System. Facial shape was analysed using geometric morphometrics. Analysis of the relationships between 14 AUs and 13 morphological parameters revealed that women display more intense facial movements, but men exhibit a tighter link between facial movements and facial structures. Next, we used Principal Component Analysis for a broader categorisation. The principal components (PCs) of the AU data corresponded to groups of AUs, revealing specific facial expressions. Three of the expressions thus identified were the same in both sexes, while the fourth was sex specific. The PCs of the morphometric data were more mosaic in composition; however, one male and one female PC largely agreed, reflecting a similar facial-shape phenotype. In both sexes, this facial shape dimension was associated with the tendency to produce a Duchenne smile. In turn, the expression of a Duchenne smile systematically affected how people in the videos were judged by an independent panel on various attributes (e.g., generosity, trustworthiness, happiness). In men, a male-specific PC of the morphometric data corresponded to facial masculinity, as determined by Linear Discriminant Analysis. Men with more masculine facial shapes were more likely to produce lower-face anger expression. We conclude that natural facial expressions are to a certain extent related to facial morphology, especially in men.
People's perceptions of their mate value-a compilation of characteristics that are desirable to potential partners-functionally guide their mating behaviors. Hormonal contraceptives alter the hormonal profiles linked to some characteristics underlying women's mate value (e.g., fertility, sociality, potential parenting ability). Thus, relative to naturally cycling women, women using hormonal contraceptives may perceive such characteristics more negatively (due to suppressed fertility) or positively (due to possible bolstered sociality and/or potential parenting ability). The purpose of this research was to test these competing possibilities. Study 1a and 1b utilized samples of single, undergraduate women and newly married women, respectively, to test the association between hormonal contraceptive use and a commonly used proxy for self-perceived mate value-self-perceived mating success. Study1b additionally tested whether the association emerged independently of sexual frequency. Study 2 tested the robustness of the observed association, using a larger sample of single women and a measure assessing perceived characteristics underlying mate value rather than perceived mating success. We then conducted a mini-meta-analysis to estimate the average effect size for all relevant effect sizes available to date. Across studies, women using hormonal contraceptives rated mate-value-relevant traits and outcomes more positively than naturally cycling women. This association is not due to sexual motives or sexual behaviors. The current research adds to a growing literature revealing differences in mating and relationship psychology between women who do versus do not use hormonal contraceptives.
In recent years there has been much research regarding the extent to which behavioural immune system (BIS; behavioural responses that evolved to detect and avoid pathogens) is related to a variation in social profile and personality traits such as extroversion among individuals. However, most research on the relationship between BIS and sociality is based on short-term experimental studies and thus little is known about the degree to which BIS is related to the actual frequency of day-to-day proximity contacts. We used data obtained from secondary students (n = 84, age 16-19yo, n schools/classes = 3) to determine whether the variation in BIS values is associated with the frequency of proximity contacts. Proximity data were derived from sensors registering the proximity of other classmates within a 2 m radius. Students belonging to the same class were wearing proximity sensors within the school environment for the period of 4 weeks. BIS activity was assessed using a total score of Perceived Vulnerability to Diseases (PVD) questionnaire. Our findings, based on real-world face-to-face proximity patterns, do not support the assertions of previous studies suggesting that BIS activation, as reflected in higher PVD values, is associated with a lower rate of social interactions. However, this does not rule out the existence of the relationship under investigation. Future studies should include larger samples and analyses of other measures of integration within close social networks.
Most research on human parental investment has focused on overall parental effort or resource allocation, overlooking the fact that human investment spans a broad suite of material, instructional, and social forms of investment. This array of investment enables examination of how evolutionary processes have elaborated parental care into distinct domains. Where daughters and sons historically faced different recurrent adaptive problems, selection should have favoured biases in parental investment that cultivate in each offspring the competencies relevant to its sex-specific challenges (e.g., navigating greater reproductive costs for daughters; navigating contest competition for sons). Likewise, mothers and fathers should differ in parental investment domains where their own evolutionary and life histories afforded greater sex-specific expertise. To test these hypotheses, we used linear mixed-effect models to analyse 105 adults' (49.5% female) ratings of parental investment received across 73 behaviours organised into 13 domains. Results were largely consistent with predictions. Daughters received more parental investment in mating and relationship guidance, protection, and material support. Sons received greater parental investment in athletic training, permissiveness regarding sexual behaviour, and competitive encouragement. Mothers invested more than fathers in direct care, bonding, social and moral guidance, and discipline. Fathers invested more in athletics, and mechanical and practical skills. Domains linked to adaptive challenges common to both sexes (e.g., direct care) showed no offspring-sex differences in parental investment. The patterns accord with the evolutionary hypothesis that parental investment maps onto sex-differentiated adaptive problems. Discussion explores hypotheses about the interactions between socialisation practices of parents and sex-linked predispositions in offspring.
Humans are uniquely adept at cultivating positive, xenophilic relationships beyond their immediate group, forming bonds through various mechanisms such as trade, exogamy, and shared defense. Despite the significance of intergroup cooperation, synthetic approaches to understanding the evolutionary, ecological, and institutional drivers of xenophilia remain underdeveloped compared to the wealth of research on intergroup conflict. Here, I synthesize ethnographic, archaeological, psychological and comparative evidence to argue that xenophilia is supported by recurrent human cognitive and social capacities whose expression and stability depend on ecological, economic and institutional contexts. The aims of this paper are threefold: first, to clarify the selective pressures and incentives that favour peaceful intergroup relations, with particular attention to factors contributing to amicable intergroup ties and expanding the circle of tolerance and cooperation, including economic interdependence through trade and reciprocity, information exchange, exogamy, and the necessity of collective defense against external threats; second, to examine how these different drivers of xenophilia interact and under what conditions they generate, stabilize or fail to sustain intergroup tolerance; and third, to place human xenophilia in comparative perspective by highlighting both parallels and distinctions with non-human primates in their strategies for fostering intergroup peace. By distinguishing between mechanisms that generate cooperation and those that stabilize it in the face of freeriding and defection, this synthesis highlights how humans uniquely scale and institutionalize intergroup peace. This perspective is particularly timely, as uncovering the evolutionary roots of tolerance and cooperation across group boundaries remains crucial for addressing pressing global challenges such as climate change, poverty, famine, conflict, and disease.
In the current study, we assessed the role of caregiving in testosterone reactivity by examining whether and how testosterone changed in romantic partners as they jointly cared for an “infant simulator,” a lifelike doll designed to mimic many of the behaviors of a real infant. Although testosterone often declines as a function of caring for a child, especially when parents feel able to meet the child’s needs, less is known about joint caregiving with romantic partners. Couples without children (N = 30; 60 participants) engaged in a joint caregiving task in the laboratory before and after taking care of the infant at home, allowing us to examine how testosterone reactivity changed over time and with caregiving experience. We found that, on average, both female and male participants showed significant post-caregiving declines in testosterone following the second, but not the first, lab session. These findings were not mediated by participants’ feelings about or performance during the at-home caregiving. Results were, however, moderated by participants’ comfort with babies and their expectations about parenting: Participants who were less comfortable with babies or had less positive parenting expectations showed larger differences in reactivity across sessions, suggesting that caregiving experience may have contributed to testosterone declines in the second session. Our findings suggest that those with more caregiving experience or who had more positive expectations about parenting were more easily able to lean into nurturance, perhaps leading to testosterone declines. Taken together, our findings reflect the nuanced, situation-dependent influences on testosterone in dyadic contexts.
Sexual orientation may be shaped, in part, by organizing effects of gonadal steroids during development. However, the interpretation of associations between sexual orientation and markers of such organizing effects may be hampered by the use of Kinsey-type scales of hetero-/homosexuality, because they assess sexual orientation from the individual's (i.e., egocentric) perspective and inherently represent a difference score between attraction to women versus attraction to men, with unclear meaning of medium scores. Using illustrative data from three studies, we show that a clearer and more consistent pattern emerges once one uses measures of sexual orientation that assess sexual attraction from the (allocentric) perspective of one's object of attraction; that is, as attraction to women (gynephilia) and to men (androphilia). We find that, in both men and women, gynephilia is negatively, and androphilia positively, associated with digit ratio, a measure of the relative prenatal exposure to testosterone versus estradiol. This suggests that relatively more exposure to testosterone predisposes individuals to be more attracted to women and less to men and vice versa for relatively more exposure to estradiol. We also find that ulna-to-fibula ratio, a putative marker of pubertal steroid effects, is positively associated with gynephilia, particularly in men, suggesting that relatively more testosterone exposure during puberty may be another source of individuals' sexual attraction to women. When we constructed a Kinsey-type measure of homo-/heterosexuality from androphilia and gynephilia scales, our findings for digit ratio replicated those reported in the literature for generic Kinsey-type scales. But we argue that the findings we obtained with allocentric gynephilia and androphilia measures are more straightforward to interpret.
Sexual orientation may be shaped, in part, by organizing effects of gonadal steroids during development. However, the interpretation of associations between sexual orientation and markers of such organizing effects may be hampered by the use of Kinsey-type scales of hetero-/homosexuality, because they assess sexual orientation from the individual’s (i.e., egocentric) perspective and inherently represent a difference score between attraction to women versus attraction to men, with unclear meaning of medium scores. Using illustrative data from three studies, we show that a clearer and more consistent pattern emerges once one uses measures of sexual orientation that assess sexual attraction from the (allocentric) perspective of one’s object of attraction; that is, as attraction to women (gynephilia) and to men (androphilia). We find that, in both men and women, gynephilia is negatively, and androphilia positively, associated with digit ratio, a measure of the relative prenatal exposure to testosterone versus estradiol. This suggests that relatively more exposure to testosterone predisposes individuals to be more attracted to women and less to men and vice versa for relatively more exposure to estradiol. We also find that ulna-to-fibula ratio, a putative marker of pubertal steroid effects, is positively associated with gynephilia, particularly in men, suggesting that relatively more testosterone exposure during puberty may be another source of individuals’ sexual attraction to women. When we constructed a Kinsey-type measure of homo-/heterosexuality from androphilia and gynephilia scales, our findings for digit ratio replicated those reported in the literature for generic Kinsey-type scales. But we argue that the findings we obtained with allocentric gynephilia and androphilia measures are more straightforward to interpret.
The evolution of schizotypy/psychosis-proneness has rarely been empirically investigated despite there being several conceptual propositions about its potential to be targeted by natural selection: mutation-selection balance, adaptiveness via creativity, and adaptiveness within fast life history evolution. We tested these hypotheses by examining the associations between psychosis-proneness (measured by trait Disintegration) and fertility (the number of children and age of first reproduction - AFR), physical health, mating behavior (short-term mating, long-term mating, and romantic attachment), environmental conditions, and creativity in two studies conducted in Serbia. Study 1 (N = 685) showed negative associations between psychosis-proneness and the number of children and AFR, followed by positive links between insecure attachment and environmental harshness. Study 2 (N = 2490; the sample was representative for the Serbian population) resulted in negative associations between psychosis-proneness and AFR and physical health, followed once again by positive links to insecure attachment and harsh ecological conditions. Interaction between psychosis-proneness and creativity in the prediction of fertility was not significant in either study. Hence, both studies show congruent results suggesting that variation in psychosis-proneness may be maintained by mutation-selection balance, but also possible adaptive features as a part of fast pace-of-life, expressed primarily by an earlier age of first reproduction. The results have implications for our understanding of the current evolution of psychosis-proneness.
Schelling (1960) and Frank (1988) famously offered commitment as an explanation of the stability of human cooperation in the face of incentives to cheat. Reputationally-enforced commitments were part of the explanation for human cooperation for much of our history (Khan, 2024, 2025). In this article, I consider the origins and effects of institutionalised commitments. These are commitments which are contractually enforced by third parties, rather than only reputationally enforced. I discuss how these commitment offer advantages for securing cooperation over and above our previous forms of commitment. I then offer an account of their potential origins. I suggest that a change in our cooperative landscape and organisational structure occurring in the Neolithic -- in particular, the rise of agricultural economies and hierarchical society -- opened the door to a new means of enforcement for commitments, affecting the success of our cooperative practices.
The Desperation Threshold Model (DTM) seeks to explain conflicting findings about the risk propensity of people living in poverty. It makes assumptions about their experiences: that they have a conception of basic needs, that their ability to meet these motivates their decisions, and that they modulate risky decisions depending on their ability to do so. The realism of these modeling assumptions has not yet been investigated. To start filling this gap, we investigated experiences of poverty through the lens of the DTM, using two complementary approaches: a pre-registered online survey with British participants (n = 300) and semi-structured qualitative interviews with very low-income individuals in France (n = 14). Our results imply that basic needs have both a context-general component and context-specific elaborations. Furthermore, participants often relied on social and institutional resources when experiencing financial adversity, indicating that only measuring personal income or wealth might not accurately capture the resources available to people. With respect to the DTM’s main predictions, most individuals close to—but still above—the desperation threshold exhibited caution and took a safety-first approach, consistent with risk-averse behavior. Risky or antisocial behaviors (e.g., cheating, stealing) emerged only in rare instances of severe financial hardship and complete lack of external support. These results suggest that the DTM’s main assumptions are empirically grounded but that they need to be qualified in specific ways. They also suggest that abstract models like the DTM can capture something about the experience of people living in conditions of poverty.
Naturalistic observations of conflict events documented that, similarly to nonhuman primates, human bystanders take an active role in managing the negative consequences of the conflict. However, although in nonhuman primates it has been suggested that bystanders affiliate with each other to decrease the social tension generated by the conflict, in humans affiliation as a stress-response in naturally occurring conflicts has not been documented yet. By applying observational methods from primatology, we conducted video analysis of streets fights recorded by surveillance cameras in public spaces of Amsterdam in order to evaluate whether conflicts promote bystanders’ affiliation as a tension-reduction mechanism. We found that witnessing a street fight increased the expression of anxiety-related behaviours in bystanders and their propensity to engage in non-physical and physical affiliative interactions with other bystanders and the conflict parties. The occurrence of physical affiliation improves in turn the emotional state of bystanders by reducing the expression of anxiety-related behaviours. By offering a behavioural-based analysis of the role of social affiliation in the post-conflict context, our approach allows to reveal that some mechanisms to cope with social tension observed in nonhuman primates can lead to similar management dynamics in human bystanders.
Perinatal women must navigate decisions about health and wellbeing for both themselves and their offspring while confronted with information, sometimes conflicting, from numerous sources. Advances in technology and information literacy have increased the amount of information available to pregnant and postpartum individuals, which can be helpful, but sometimes confusing. This raises questions about which sources of information perinatal individuals trust, find credible, and rely on for advice, and how sources may differ across generations. In the current study, a global sample of 386 mothers and 102 grandmothers responded to an online survey about trust, credibility, and reliance on various sources of information during pregnancy and postpartum. Overall, medical sources were more trusted than family and digital sources, and recent mothers reported higher trust in medical sources than did grandmothers. When looking at perceived credibility of different sources, participants’ own mothers were rated as most credible overall, while recent mothers rated medical providers, their own mothers, and friends as more credible than the grandmothers did. Both mothers and grandmothers reported the highest reliance on medical sources for perinatal information, however, recent mothers relied more on medical providers and online sources than did grandmothers, and grandmothers relied more on their own grandmothers and related peers than the mothers did. These findings are consistent with research showing that perinatal people trust and rely largely on information from medical providers along with other information sources, but also suggest that generational shifts in perinatal perceptions and reliance on information sources may be occurring.
The origins and function of dowry have been debated since the 1970s, leading to two hypotheses: the compensatory hypothesis and the inheritance hypothesis. In this article, we suggest to redefine dowry on the basis of both a legal and an economic characterization. We show, using Testart et al. (2002) and ethnographic data on hunter-gatherer societies of the Northwest Coast, that these societies can be considered to have practiced dowry. The inclusion of these societies in the group of dowry societies has important consequences for the analysis of the origin and function of this transaction. We propose here an economic and ecological model of its origin and function which shows that this marriage transaction is a double compensatory gift (gift of a daughter, gift of wealth) aimed at encouraging families to integrate an unproductive member into the domestic unit (whether this unproductivity is real or perceived). Dowry thus appears in societies where the articulation of the gender division of labor and particular ecological or economic conditions cause women’s contribution to the production of raw food goods to fall below a minimum threshold relative to men's economic strategies, adding new elements to the compensatory hypothesis.
The study of partner preferences in historical populations is constrained by the limited information available in historical sources. These limitations make it difficult to assess the role of characteristics such as physical attractiveness or psychological traits in spouse selection. Instead, this study examines patterns of marriage partner choice among 19th‑century residents of Poznań, Poland, with particular attention to observable factors including place of origin, occupation, denomination, and age at marriage. The research material contained individual information on 15,652 marriages contracted between 1830 and 1900 in seven Poznań parishes. The partners were divided into four categories based on their marital status: first marriages, marriages of remarried men or women, and second marriages. The analyses included correlation, linear regression, Analysis of Variance, and chi-square tests. First and second marriages differed in the age at marriage of men and women, suggesting that motivations and criteria for marriage changed with life stages and marital history. Specifically, individuals entering the first marriages were the youngest, while divorced or widowed individuals who married within their own marriage category were older than those who married someone who had never been married. First marriage individuals had smaller age differences, but the lowest age correlations compared to all other categories, except remarried women who often married men of similar age or even younger. Across all marriage categories, partners exhibited strong homogamy in denominational, geographical, and social backgrounds, emphasizing the influence of social and cultural factors on marital choices. The origin of the spouses played an important role in partner selection, revealing the impact of the geographical context on the timing of marriage. Specifically, marriages were delayed when at least one partner originated from an urban area and in migrants compared to local population. Marital decisions were also shaped by age and social position, e.g., older men with higher socioeconomic status were more likely to marry younger women. However, these partner selection criteria differed between first and subsequent marriages. The findings of our study support established concepts of marriage patterns while illustrating how biological considerations, geographical contexts, social norms, and economic forces jointly shaped personal choices in historical societies.
The study of partner preferences in historical populations is constrained by the limited information available in historical sources. These limitations make it difficult to assess the role of characteristics such as physical attractiveness or psychological traits in spouse selection. Instead, this study examines patterns of marriage partner choice among 19th‑century residents of Poznań, Poland, with particular attention to observable factors including place of origin, occupation, denomination, and age at marriage. The research material contained individual information on 15,652 marriages contracted between 1830 and 1900 in seven Poznań parishes. The partners were divided into four categories based on their marital status: first marriages, marriages of remarried men or women, and second marriages. The analyses included correlation, linear regression, Analysis of Variance, and chi-square tests. First and second marriages differed in the age at marriage of men and women, suggesting that motivations and criteria for marriage changed with life stages and marital history. Specifically, individuals entering the first marriages were the youngest, while divorced or widowed individuals who married within their own marriage category were older than those who married someone who had never been married. First marriage individuals had smaller age differences, but the lowest age correlations compared to all other categories, except remarried women who often married men of similar age or even younger. Across all marriage categories, partners exhibited strong homogamy in denominational, geographical, and social backgrounds, emphasizing the influence of social and cultural factors on marital choices. The origin of the spouses played an important role in partner selection, revealing the impact of the geographical context on the timing of marriage. Specifically, marriages were delayed when at least one partner originated from an urban area and in migrants compared to local population. Marital decisions were also shaped by age and social position, e.g., older men with higher socioeconomic status were more likely to marry younger women. However, these partner selection criteria differed between first and subsequent marriages. The findings of our study support established concepts of marriage patterns while illustrating how biological considerations, geographical contexts, social norms, and economic forces jointly shaped personal choices in historical societies.
This paper challenges the social constructionist perspective on sex and gender, which argues that gender is solely shaped by cultural norms and that biological sex exists on a spectrum. The research addresses whether biological evidence, including evolutionary psychology, neuroscience, and hormonal studies, contradicts the claims of social constructionism. Furthermore, the study critiques mainstream frameworks, such as the American Psychological Association’s guidelines, which emphasize the role of culture while disregarding biological underpinnings. The paper employs a multidisciplinary review of existing literature and research from evolutionary psychology, neuroscience, economics, and cross-cultural studies. Data from developmental biology, hormonal studies, and behavioral research are synthesized to evaluate biological differences between human males and human females. These findings are then compared with the claims of social constructionist theorists. Critical analyses of policies and guidelines, such as the APA’s position on masculinity, are included to illustrate the implications of social constructionist views in practice. The analysis demonstrates that biological factors such as hormones, brain structures, and evolutionary processes significantly influence sex and gender. Evidence from neuroscience reveals structural brain differences between human males and human females, while studies in developmental biology underscore the impact of prenatal hormone exposure on behavior. Cross-cultural research shows consistent gendered behaviors, challenging the assertion that gender is merely a social construct. Furthermore, the failure of conversion therapies supports the biological foundation of sexual orientation. The findings refute the core tenets of social constructionism, affirming the biological reality of sex and gender. While acknowledging the role of culture in shaping gender expressions, the study emphasizes the importance of respecting scientific evidence to inform policy and social discourse. A balanced approach that integrates biological and cultural perspectives is advocated, promoting inclusivity without undermining empirical reality.
In this paper, I examine the widespread phenomenon of decline narratives in human societies, where the past is idealized as a “golden age” characterized by extraordinary abundance, strength, longevity, and supernatural powers, in contrast to a flawed present. Drawing on ethnographic, historical, and psychological evidence, I explore the cultural manifestations and cognitive foundations of these narratives. The analysis highlights the roles of cognitive biases such as rosy retrospection and narrative inflation, as well as the strategic use of temporal distancing to rationalize fantastical beliefs by situating them in a distant, unfalsifiable past. By comparing decline narratives in traditional societies with progress narratives in post-Enlightenment, modern contexts, I explore how these frameworks shape cultural attitudes toward tradition and change, and consider their broader implications for understanding how cultural narratives influence human behavior.
