Laith Al-Shawaf awarded the Evolution in the Public Eye Award

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HBES Members,

I am thrilled to announce that our Laith Al-Shawaf has just been awarded the Evolution in the Public Eye Award.

The EPE Award honors outstanding contributions to the public understanding of evolutionary perspectives on behavior. These contributions positively impact our perception and understanding of evolutionary science by communicating accurate, evidence-based information and/or exposing and countering misinformation and misleading claims. Through social media, community blogs, academic outreach, or other forms of science communication, honorees have helped foster more informed and nuanced public discourse about evolutionary science. This award recognizes those whose efforts strengthen the bridge between rigorous research and public understanding, helping ensure that evolutionary perspectives are represented accurately in broader societal discussions.

For more information including details on award ceremony please follow this link.

Do human faces, bodies, and voices “tell the same story” about attractiveness, health, and dominance

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– by Tobias L. Kordsmeyer

When we form impressions of others, we rarely rely on just one cue. Faces provide one stream of information, bodies provide another, and voices add yet another layer. In everyday life, these cues are usually perceived together – so it is tempting to assume they are redundant. If someone has an attractive face, we might expect an attractive body and an attractive voice as well.

But should we indeed expect that kind of cross-modal consistency, i.e. noteworthy correlations of perceptions of attractiveness and other socially relevant traits between faces, bodies, and voices? Two competing ideas about such correlated perceptions have been debated for decades.

The one ornament hypothesis (also called backup signals hypothesis or redundancy hypothesis) proposes that different body parts and modalities reflect shared underlying qualities such as immunocompetence, genetic quality, or developmental stability. If that were true, then perceptions of attractiveness (and related traits like health or dominance) should correlate across faces, bodies, and voices.

By contrast, the multiple messages hypothesis argues that what different modalities signal is more independent: faces might reveal different information (e.g. based on how average faces are, which in turn is related to perceptions of attractiveness and health), than bodies (e.g. health based on shape and fat distribution) and voices (e.g. dominance and masculinity based on voice pitch). If so, correlations among perceptions across modalities should be weak or absent – because each channel carries partly distinct information.

Our study puts these ideas to a rigorous test by asking a seemingly simple question: When people judge faces, bodies, and voices separately, do those ratings line up? Put differently, are perceptions of attractiveness, dominance, and health correlated positively across faces, bodies, and voices? Additionally, steroid hormones (testosterone, estradiol), which influence the development of facial, bodily, and vocal characteristics, were investigated as partial explanations of purportedly correlated perceptions.

To investigate these questions, we assembled a large stimulus set from 320 men and women, including neutral face photographs, 3D body scans converted into short rotating videos, and brief voice recordings. Each of these three modalities was then judged by separate groups of raters regarding perceived attractiveness, perceived health, and perceived physical dominance (the latter conceptualised as the likelihood of winning a physical fight). That separation matters – if the same raters had judged faces, bodies, and voices, halo effects could have inflated correlations (“I liked his face, so I feel like his voice must be attractive, too”). Using different groups of raters for different modalities is a tougher test of true cross-modal concordances.

A major methodological concern in older work on judgments of bodies was that body stimuli often included skin colour and texture, which themselves convey health-related information and could invoke stereotypes, which could create shared variance with facial appearance. In our study, we deliberately used grey-coloured body scans without heads, removing skin tone cues, to shift the focus to body shape. That means any face–body correlations that remain are harder to explain away as “it’s just skin quality.”

What did we find? Generally, we found consistent and medium-sized correlations between faces and bodies for all three traits: attractiveness, health, and physical dominance. On average, people who were considered attractive in terms of their facial features were also considered attractive in terms of their body shape. Correlations for perceived health and perceived physical dominance were similar, but only slightly smaller. So, at least for faces and bodies, the data look consistent, indicating a partly redundant signal and hence supporting the one ornament hypothesis.

For voices, however, the story shifts. Out of the six correlations of voices with faces and bodies for the three traits, only three were significant, and effect sizes rather small. Thus, regarding voices, the multiple messages hypothesis seems to be better supported, and voices may add information that is not strongly predictable from faces or body shape.

When we split the target sample by sex, the face–voice and body–voice correlations were somewhat stronger for men than for women (especially for perceived health and physical dominance), whereas the body-voice correlations were more comparable across the sexes. Thus, whether the one ornament hypothesis or multiple messages hypothesis is more valid may not only depend on the modality, but may also differ by target sex.

A common idea in evolutionary psychology is that sex steroid hormones contribute to the development of sexually dimorphic traits (including facial masculinity/femininity, body composition including fat distribution, and vocal characteristics), which then influence perceptions of attractiveness, health, and dominance. If that’s right, one might expect that part of the cross–modal correlations exists because the modalities are simultaneously influenced by the same endocrine factors.

We tested this using salivary hormone measures: baseline testosterone and testosterone reactivity (after having engaged in a dyadic competition in the laboratory) in men, and baseline testosterone, baseline estradiol, the baseline testosterone/estradiol ratio, as well as hair testosterone (a measure of long-term aggregated baseline levels) in women.

The insight from these additional analyses was rather simple: We found no evidence that these hormone measures explained the cross-modal correlations. The study did find a few small direct associations between men’s baseline testosterone and their vocal attractiveness and physical dominance, but not in a way that explained the broader cross-modal pattern.

One implication is that if a shared biological mechanism links facial, bodily, and vocal characteristics, it may not be well captured by current adult hormone levels. Instead, prenatal or pubertal hormonal measures with more organisational effects during development, or additional genetic factors and environmental perturbations during development may play a stronger role as explanatory mechanisms.

What is the take-away message? This study offers a nuanced update to a debate that is sometimes framed too starkly as “redundant” versus “independent” signals. For faces and bodies, we demonstrate moderate associations across perceived attractiveness, health, and physical dominance (somewhat stronger in men than women). That supports the idea that these visual channels share underlying cues – despite the body stimuli in our study lacking skin information – in support of the one ornament hypothesis. However, for voices, cross-modal correlations were rather weak, suggesting voices may communicate partly distinct information from faces and bodies – more consistent with the multiple messages hypothesis. Concerning potential explanatory mechanisms for such cross-modally correlated perceptions, at least current adult testosterone and estradiol levels do not seem to play a role here, calling for the investigation of alternative causes.

Tobias L. Kordsmeyer, Philine A.C. Rasokat, Julia Stern, Christoph Schild, and Lars Penke. 2026. Correlated perceptions and underlying hormonal factors of bodily, facial, and vocal attractiveness, health, and physical dominance. Evolution and Human Behavior 47 (2): 106818.

Health, Attractiveness, and Mate Choice in Central Africa

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– by Bonnie Hewlett, Harshita Agrawal, and Barry Hewlett

In the high-pathogen rain forests of central Africa, adolescents begin evaluating who looks healthy, attractive, and potentially marriageable in environments that differ markedly from those studied in urban industrial settings. What cues signal health, and which of those cues actually matter?

Evolutionary researchers have long argued that in many species, parasite loads provide clues to the health and attractiveness of potential mates. Beauty and marriageability are rarely separate from assumptions about strength, fertility, and resilience. But what actually counts as a visible sign of health? And do those signs mean the same thing in different cultural settings?

Health is not just a biological condition—people often believe it is written into the body. But when people judge whether someone looks healthy or attractive, are they making quick decisions that reflect evolved sensitivities or local cultural expectations? If you are an adolescent thinking about marriage, how would you evaluate who would make a good spouse? How accurately can people judge physical health from appearance, and how do those judgments shape perceptions of attractiveness?

This study examined these questions with adolescents in two neighboring but culturally distinct communities: Aka hunter-gatherers and Ngandu farmers in central Africa. The Aka are mobile hunter-gatherers who emphasize egalitarianism, autonomy, and pronounced cooperation in subsistence and childcare. Daily life revolves around food sharing, mobility, and close interpersonal relationships. The Ngandu, in contrast, are sedentary agriculturalists organized around patrilineal clans. Farming, hierarchy, and public reputation shape village life.

These groups live in the same rain forest environment and interact regularly. Yet their cultural values and subsistence strategies differ substantially. The cultural-ecological setting offers an opportunity to examine how evolved propensities and culture shape perceptions of health and attractiveness.

The study included 75 adolescents (39 Aka and 36 Ngandu), spanning roughly from puberty to first marriage at age 20. Participants evaluated all photographs of peers from their own community, sorting them into categories: Who looks healthy? Who is attractive? Who seems marriageable? Participants were then asked to explain why someone looked healthy, attractive, or marriageable.

At the same time, we collected objective biomarkers of physical health, including Body Mass Index (BMI) and parasite load from stool samples. This allowed us to evaluate whether perceptions of attraction and health were linked to biomarkers.

One result stood out clearly: in both groups, BMI predicted which adolescents were perceived as healthy and attractive. Parasite burdens did not.

Across statistical models, each one-unit increase in BMI significantly increased the likelihood of being rated healthy. BMI also significantly predicted attractiveness ratings.

It is important to remember that both Aka and Ngandu adolescents have BMIs at the very low end of global distributions—often below the 5th percentile of U.S. adolescents. In this setting, small differences in body mass may signal something very different from what they do in urban industrialized societies. In environments marked by food insecurity and high pathogen exposure, modestly higher BMI may reflect adequate energy balance, resilience to infection, and physical robustness. Visible physical condition, in other words, functions as a salient cue of health.

Even more striking, perceived health strongly predicted both attractiveness and marriageability. Adolescents did not treat beauty as separate from health. Health anchored attraction.

What about parasites? Evolutionary theory, particularly the Hamilton–Zuk hypothesis, suggests that parasite resistance may serve as an honest signal of genetic quality. If so, individuals with lower parasite loads should be perceived as healthier or more attractive.

That is not what we found.

Across multiple statistical models and biologically meaningful measures of parasite burden, parasite load did not reliably predict perceptions of health or attractiveness.

Why?

In these communities, parasitic infections are widespread. When nearly everyone carries multiple parasites, differences may not be easily noticeable or socially significant. Adolescents tend to rely on broad, observable cues, such as BMI, rather than signs from underlying infection status.

Parasites matter biologically. But they may not be perceptually salient in everyday social judgments.

How did the cultural setting impact who was considered healthy or attractive? Although BMI mattered in both communities, cultural diversity also impacted the variability in how adolescents described attractiveness.

Among the Aka, youth emphasized kindness, cheerfulness, sociability, and “walking with strength.” Physical traits were noted, but personality and vitality were more salient. In small, cooperative foraging camps, prosocial temperament and reliability are adaptive traits in a partner.

Ngandu adolescents, by contrast, more often highlighted clean clothing, bodily cleanliness, good posture, and beauty and facial features. In sedentary farming villages where reputation and public presentation matter, outward appearance can signal discipline, productivity, and social standing.

Both groups valued health. Both valued cleanliness. But they weighted social versus aesthetic cues differently—reflecting their distinct culturally constructed niches.

How did gender influence evaluations of attraction, given evolutionary theories that predict sex differences in mate preferences?

Interestingly, health ratings were relatively consistent across raters of both sexes, reinforcing the idea that visible body condition serves as a broadly shared cue. On the other hand, male raters showed greater variability and, in some cases, stricter standards when judging females. Female raters were more consistent in their judgments and showed strong associations between BMI and male marriageability.

What do these findings tell us?

First, some aspects of mate preference, such as attention to visible cues of body condition, are common across cultural contexts, indicating that human mate preferences reflect shared psychological architectures.

Second, the shared psychological architectures and meanings of those cues are impacted by culturally constructed niches. In wealthy industrialized cultures, higher BMI may signal disease risk. In small-scale cultures with high variability in daily food supply, modestly higher BMI may signal resilience and adequacy.

Third, not all biologically relevant indicators of health are socially salient. Parasite burden, despite its evolutionary relevance, did not appear to strongly shape social evaluations in this setting.

Most importantly, our findings illustrate a central insight of evolutionary anthropology. Human mate preferences reflect shared psychological architecture, but that architecture is expressed through local ecologies and cultural models.

Aka adolescents emphasize a cooperative temperament in a mobile foraging way of life. Ngandu adolescents emphasize presentation and robustness in farming villages. Both reflect local realities and constructed niches.

Adolescents in the rainforest of central Africa are not enacting abstract evolutionary scripts. They are navigating real-world trade-offs—between health, cooperation, productivity, and reputation.

Understanding how these judgments emerge at the intersection of ecology, evolutionary psychology, and culture reveals that mate preferences are neither purely universal nor purely cultural. They are biocultural: grounded in evolved sensitivities, filtered through ecological settings, and expressed through culturally meaningful ideals.

Beauty, it turns out, is not just in the eye of the beholder—it is in the cultural ecology of survival.

Bonnie Hewlett, Harshita Agrawal, and Barry Hewlett. 2026. Health, attractiveness, and marriageability among Aka hunter-gatherers and Ngandu farmer adolescents and young adults in the Central African Republic. Evolution and Human Behavior 47 (2): 106815.

The Surprising Roots of Primate Sexuality: What Baby Monkeys’ Behavior Reveals About the Origins of Sexual Behavior

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– by Irene Delval and Solimary García Hernández

Traditionally, scientific and popular assumptions about sexual behavior have struggled to decouple it from its reproductive purpose. From primates to nematodes, sexual behaviors that didn’t lead to conception were often dismissed as errors, curiosities, byproducts, or evolutionary leftovers.

Recently, however, this perspective has shifted. In Western societies, as social standards have changed and the visibility of LGBTQIAPN+ communities has grown, science has moved away from restrictive moral ideals to explore the diverse functions of sexuality. The scientific community now recognizes that across many species, including ours, sexual behavior serves a range of social functions like bonding, conflict resolution, reconciliation, or relationship maintenance. This has fueled growing interest in non-conceptive sexual behavior. Much of the research in this area has focused on Same-sex Sexual Behavior (SSB). Once framed as a Darwinian paradox, SSB is now understood as a functional and adaptive component of mammalian social systems. We now know that SSB is a prevalent trait in primates, driven by ecological and social pressures in socially-living species.

Yet, one form of non-conceptive sex remains largely unexplored: the sex-like behaviors that happen before sexual maturity, in prepuberal subjects, long before individuals develop reproductive drives. This begs a major question: how and when do these behaviors first emerge? Understanding this timeline can tell us a lot about their evolved functions.

In our new research published in Evolution and Human Behavior (March, 2026), we explored how sexual behavior emerged during the first year of life in two species of wild robust capuchin monkeys (Sapajus libidinosus and S. xanthosternos). By following 16 wild infants longitudinally in Brazil, our team provided a rare window into the development of sexual behavior under natural conditions. Our findings flip the traditional view that young primates (including humans) engage in sexual behavior merely to practice for adult reproduction, providing strong evidence for the growing consensus among researchers that, across primate species, sexual interactions help animals navigate their social worlds long before they can reproduce.

Starting from Month One

The biggest surprise was just how early these behaviors begin. Both male and female infants exhibited socio-sexual behaviors (i.e., behavior sexual in form but serve but serve social functions), such as mounting, genital inspection, and courtship gestures, within their first month of life. This remarkably early onset parallels observations in humans and shows that sexual behavior doesn’t simply lie dormant until puberty. Instead of appearing suddenly at sexual maturity, it seems to be part of the behavioral repertoire from the very beginning, at least in its early-developing form.

Even though the two capuchin species live in very different environments (one in semi-arid scrubland, the other in tropical rainforest), their developmental trajectories were similar. Among a repertoire of 25 analyzed sexual behaviors, both species and sexes shared the six most frequently performed behaviors. However, although males and females initially performed the same types of behaviors, like eyebrow raising, chest rubbing or mounting, which are usually performed during adult heterosexual courtships, sex differences emerged as the infants grew.

Early and Marked Sex Differences

Male infants showed higher rates of sexual behavior, greater behavioral diversity, and an earlier onset compared to females. The increase in the emergence of sexual behavior over time was also steeper in males, indicating a sex-specific developmental trajectory. These findings align with research in other primates, such as macaques, and suggest that sex differences in sociosexual behavior emerge early in ontogeny, likely shaped by genetic and hormonal effects right from the start.

What makes this particularly fascinating is that in adult robust capuchins, courtship is predominantly female-led. Adult females are the proactive agents, using elaborate facial expressions and even throwing stones to get the attention of often-indifferent males. If the classic “practice hypothesis” were true, which assumes infants perform early forms of these behaviors to rehearse their future adult roles, we would expect infant females to be the ones practicing the most.

However, our data revealed the exact opposite. There were large differences in the directionality of sexual behaviors. Infant males engaged in these interactions far more often, while females were usually the receivers of such behaviors. This points to a male-specific developmental pathway of arousal that clearly doesn’t just mirror adult courtship roles.

Different Partners, Different Goals

We also found a clear divide in who the infants chose to interact with. Infant males acted as sexual “extroverts,” engaging with a wide range of partners. Most notably, their most frequent partners were adult males, making same-sex interactions very common among them. Infant females, on the other hand, had much narrower preferences, mostly interacting sexually with other infants of both sexes. This divergence suggests something important: early sexual behavior likely serves completely different functions depending on the sex.

For males, these interactions might help establish social bonds, navigate dominance hierarchies with older males, or regulate arousal in complex social settings. For females, these behaviors, at this stage, seem more embedded in general peer play and social exploration. We need to further understand when sexual “awakening” occurs in female robust capuchins.

Why This Matters

Our research highlights that primate sexuality is flexible and multifaceted right from birth. Because sex differences emerge so early and don’t simply mirror adult roles, these findings open up new questions about the true origins of sexual behavior in all primates, humans included. If we want to understand the “why” of adult behavior, we first need to look closely at the “how” in the infant’s world.

Just as grooming behavior, which goes far beyond hygiene and removing parasites to act as a social glue, early sexual behavior seems relevant for building and maintaining social bonds, and canalizing arousal, rather than just preparing individuals for reproduction. Our findings also point to a broader issue: studying infant sexuality remains a highly sensitive and often avoided topic, especially in humans. This is where research on non-human primates becomes so valuable, giving us a comparative window to investigate these processes rigorously and without cultural constraints.

Delval, I., García-Hernández, S., Teles, N., Caixeta, J., Cezar, L., Valentova, J. V, Izar, P., & Leca, J-B. 2026. Early sex differences in sociosexual behavior of wild robust capuchin monkeys: Ontogenetic and evolutionary insights. Evolution and Human Behavior, 47 (2), 106834.

Abstract core knowledge may shape the basins of cultural attraction: romantic kissing as a case study

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– by Hossein Samani & Ashley J. Thomas

It may be easy for many readers to assume that romantic kissing (lip-to-lip contact between romantic partners) is universal. While romantic kissing is common around the world, it is far from universal. On the other hand, rather than spreading from a single point of origin, ethnographic and historical evidence suggests that kissing has been ‘invented’ independently at different times and places. This combination—widespread but not universal, and seemingly reinvented multiple times—is what we set out to explain. Our central claim is that romantic kissing is best understood as a cultural invention that reappears because it aligns with how humans intuitively understand intimacy. We argue that similarities in how everyone understands intimacy create a sort of gravitational pull, or “basin of attraction,” that makes some ways of signaling intimacy (like kissing) much more intuitive, and therefore more likely, than others.

To make sense of a cultural practice like romantic kissing, we broke down the question into two parts: (1) What problem does this practice solve? (2) Why does it take this particular form? Consider writing. Writing systems around the world differ in countless ways, but they all solve similar problems: they let us record and transmit information across time and space. The features of writing systems are shaped by the limits of our minds and bodies. Though diverse, writing systems around the world tend to be composed of relatively simple, easy-to-distinguish shapes that are easy to produce. We can ask the same questions about kissing. What is it for? And why lip-to-lip contact rather than the endless other actions that could signal romance? Our answer is that romantic kissing is particularly intuitive to all humans as a way to communicate and intensify intimate bonds, and it serves to convey a special kind of intimate bond, i.e., romantic love, where and when romantic love is important.

We start with the idea of “cultural attractors.” This idea, from theories of cultural evolution, argues that cultural evolution is affected by the structure of the human mind. Practices that resonate with existing biases, cognitive tools, or innate representations are easier to invent, imitate, and remember. While this process does not determine practices, over time, cultures tend to converge on practices that are easier for people to reproduce and understand. Crucially, this process doesn’t determine exact behaviors. It doesn’t include the specific practice of kissing. Instead, it shapes the landscape so that some practices that are more intuitive to understand and easy or more pleasurable to reproduce create ‘gravitational pulls’. Romantic kissing, we argue, is one such practice.

To understand why, we incorporate the idea of ‘core knowledge’ which explains how humans—starting in infancy—make sense of the world, including social relationships. Over the past several decades, research on infants has challenged the idea that babies begin life with only sensory impressions and gradually build toward abstract concepts. Instead, there is now strong evidence that infants come equipped with what’s called core knowledge: domain-specific systems that represent abstract aspects of the world—objects, agents, numbers, space. It enables infants to make sense of situations or entities the first time they encounter them and to learn quickly about their specific environment. Recent evidence suggests these ideas can be extended to social relationships. Importantly, even infants seem to distinguish between friendly and socially intimate relationships. Specifically, they link physical closeness, such as using the same spoon, to emotional closeness, such as comforting someone. In these studies, infants predicted that a woman who shared a single orange slice with a puppet by eating some herself, putting it in the puppet’s mouth, and then back in her mouth, would be the one to comfort the puppet when it was sad. We argue that because very young infants recognize this, it is likely universal, and this is why romantic kissing is intuitive.

Next, we asked about the purpose of romantic kissing. Romantic love itself seems to appear in many cultures, but its importance and distinctiveness vary. In some places and historical periods, romantic love is central to marriage, identity, and life decisions. In others, it’s less salient than, say, loyalty to kin or community, or it’s not strongly separated from other forms of affection. In societies where romantic love is not as sharply defined or highly valued, the specific need that kissing solves is less present. Other practices—such as different forms of affection, ritual, or sex—may carry the load instead. Conversely, as societies change—economically, demographically, ideologically—and romantic love becomes more salient, we would expect to see increases in both how much people talk about romantic love and how central romantic kissing becomes as a symbol of it. Our proposal is that romantic kissing becomes common and symbolically powerful in cultures where romantic love is treated as a distinct and important relationship category and where people need a clear, intuitive way to express and signal that specific bond.

Given that humans share intuitions about intimacy, lip-to-lip kissing—with very close bodily contact, synchrony, and the exchange of saliva—fits those needs extremely well. We argue that people could easily learn that kissing is a way to communicate that “this relationship is special.” Kissing itself also likely triggers intense feelings of being moved or deeply connected, which further reinforces its role. In that sense, romantic kissing functions as a cultural technology: it leverages universal intuitions to address a local social problem—how to signal, deepen, and display romantic love.

It is also possible that romantic kissing is costly. Kissing is not just intimate; it’s risky. It involves the face and mouth, carrying a risk of injury (from biting) and pathogen transmission through saliva sharing. From a signaling perspective, that’s exactly what you might want in a commitment device: something you wouldn’t do with just anyone. From an evolutionary perspective, romantic love can be a high-stakes relationship because it involves commitment to a single person. Costly signals may help distinguish genuine commitment from casual interaction.

In the end, we don’t think romantic kissing is “in our genes” in any simple sense. Nor do we think it’s a mere historical accident. Instead, we see it as a recurring cultural solution built on universal knowledge of what it means to be close to someone. By studying infants, cross-cultural data, and historical change together, we can begin to see why certain practices—like kissing—are common but not universal.

Hossein Samani and Ashley J. Thomas. 2026. Abstract core knowledge may shape the basins of cultural attraction: romantic kissing as a case study. Evolution and Human Behavior 47 (2): 106810.

Do the damaging effects of the Epstein Barr virus, the cause of the Kissing Disease, weaken the idea that kissing is an adaptation favored by sexual selection?

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– by Paul Ewald

In modern societies kissing is a widespread and important aspect of social interactions. It appears to be a sexually selected adaptation that facilitates mate evaluation, pair bonding, and/or sexual activity. This evolutionary explanation is paradoxical because kissing seems unnecessary for mate selection and is associated with transmission of diseases, which might outweigh the evolutionary advantages of kissing. The most widely recognized of these diseases is infectious mononucleosis, commonly known as the Kissing Disease. Although people with mononucleosis experience fever, body aches, and extreme fatigue, the illness itself is almost never life-threatening. People generally recover within a few weeks without any specific treatment. If that were the whole story, suffering infectious mononucleosis as a consequence of kissing would not be compelling evidence against the hypothesis that kissing is a sexually selected adaptation. However, the mounting knowledge about EBV-associated diseases indicates that kissing has more serious consequences.

The Epstein Barr virus was first accepted as the primary cause of infectious mononucleosis in 1968. About a decade later its major route of transmission in affluent populations was generally recognized to be salivary exchange during intimate kissing. Over the past half-century, EBV has been associated with severe diseases such as cancers, multiple sclerosis and systemic lupus erythematosus. Together with infectious mononucleosis, these diseases would seem to generate fitness costs that could offset or even completely negate the mating advantages of kissing, and make an adaptive explanation of kissing questionable.

If these diseases were not present during the evolutionary history of humans, this concern would disappear.

Comparisons across populations help clarify whether intimate kissing has been associated with these diseases during our evolutionary history and therefore with a high fitness cost. Specifically, if these diseases tend to occur only in modern populations with particular attributes, then their presence would not weaken the hypothesis that kissing evolved as a sexually selected adaptation.

The existing evidence indicates that infectious mononucleosis occurs primarily in modern affluent populations in which environmental disinfection is emphasized. In areas with poor hygiene, EBV infections tends to occur prior to adolescence and rarely causes infectious mononucleosis. When infectious mononucleosis does occur, it tends to be more mild than when it occurs in affluent populations. The general explanation for this difference is that kids tend to be exposed to low doses of EBV in areas with poor hygiene and therefore develop some immunity that protects them from the high doses that are associated with intimate kissing. Comparative evidence therefore indicates that infectious mononucleosis has been largely a recent consequence of EBV infection resulting from hygienic activities that increase the probability of severe infections from kissing. This conclusion has ramifications for understanding the fitness costs of kissing that arise from the more serious EBV-associated diseases.

EBV has been strongly associated with breast cancer. Comparisons of EBV positivity in breast cancers relative to control breast tissue together with effects of EBV on cellular proliferation indicate that EBV plays a causal role in about 20% of breast cancer. EBV is also now generally accepted as a cause of multiple sclerosis. The associations of EBV with breast cancer and multiple sclerosis are statistically significant only among patients who had experienced infectious mononucleosis. Because mononucleosis is a modern disease associated with delayed EBV infection, the associations of these diseases with mononucleosis indicates that they too are modern diseases associated with delayed EBV infection.

EBV is now a generally accepted cause of about half of Hodgkin’s lymphoma. Breast cancer is associated with young adult Hodgkin’s lymphoma, which tends to occur within two to three years after infectious mononucleosis in EBV positive tumors. EBV-negative tumors show no association with time since infectious mononucleosis. Like breast cancer, Hodgkin’s lymphoma therefore is associated with the more severe EBV infections in modern affluent populations.

EBV is now generally accepted as a cause of systemic lupus erythematosus. Although studies have not assessed whether lupus is restricted to individuals who have had infectious mononucleosis, lupus, like multiple sclerosis, tends to occur in affluent modern populations. The main genetic risk factor for EBV-associated multiples sclerosis is also a risk factor for lupus. It codes for a protein that EBV uses as a receptor to enter cells and became prevalent about 5000 years ago. This information suggests that lupus, like multiple sclerosis, would not have been a factor disfavoring kissing during the broader span of human evolution.

These findings indicate that the relationship between kissing transmitted EBV and these severe diseases is relatively recent, and that these diseases therefore did not generate fitness costs that would have selected against intimate kissing during the evolutionary history of Homo sapiens. The flip side of this conclusion is that intimate kissing is now more unsafe than it used to be during our evolutionary history, and humans have not evolved to be sufficiently wary of the present-day dangers of intimate kissing.

Paul W. Ewald. 2026. Epstein Barr virus, infectious mononucleosis and associated diseases as contributors to the costs of intimate kissing. Evolution and Human Behavior 47 (2): 106817.

When animals “kiss”: what nose-to-nose contact can tell us about behaviour and evolution

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– by Sophie Lund Rasmussen

Kissing is often considered one of the most human of behaviours.

It feels intimate. Emotional. Social. And perhaps even a little mysterious. Why do we do it?

Interestingly, lip-to-lip kissing is actually very rare in the animal kingdom—only documented in humans, chimpanzees, and bonobos. But if we take a step back and look more broadly, many other mammals engage in a different kind of close-contact behaviour: nose-to-nose contact.

At first glance, it looks disarmingly similar. Two animals gently touching faces. It’s easy—perhaps inevitable—to interpret it as affection.

But as is often the case in behavioural biology, what we think we are seeing and what is actually happening may be very different.

A behaviour hiding in plain sight

Nose-to-nose contact is surprisingly widespread across mammals—from solitary hedgehogs to highly social bats, pigs, and even eusocial naked mole-rats. Yet, despite being so visually obvious, it has received remarkably little scientific attention.

That gap was the starting point for this study.

By taking a comparative approach—bringing together published observations and field insights across mammal species with very different social systems—I wanted to ask a simple question:

Does nose-to-nose contact serve the same suggested purposes across species—or is it something entirely different depending on context and levels of social organisation?

Information exchange

One of the clearest patterns that emerges is that the same physical behaviour can have very different functions depending on the species.

At its core, nose-to-nose contact is about information exchange.

Mammals rely heavily on chemical cues. Through close contact, individuals can assess each other’s identity, health, reproductive status, and even social rank.

But what animals do with that information varies dramatically.

The awkward encounter of hedgehogs

Take the European hedgehog.

If you imagine two hedgehogs touching noses, it is tempting to interpret it as something friendly—even affectionate. But the reality appears far less romantic.

Hedgehogs are solitary animals. They generally avoid one another and only interact under specific circumstances, such as mating or when feeding at feeding stations with cat food provided in residential gardens.

When nose-to-nose contact does occur, it seems almost accidental—arising during mutual sniffing rather than as an intentional social gesture.

And their reaction is striking.

After touching noses, hedgehogs often recoil, freeze, and appear momentarily “switched off,” as if overwhelmed by the sensory input. They may remain in this state for up to a minute, seemingly unaware of their surroundings.

From an evolutionary perspective, this is puzzling.

Why engage in a behaviour that temporarily leaves you vulnerable to predators?

One possibility is that the information gained is so valuable that it outweighs the risk. The contact may provide a rapid and concentrated burst of chemical signals—allowing individuals to quickly assess whether another hedgehog is a threat, a potential mate, or something to avoid.

Not exactly a romantic moment.

From information to social bonding

In more social species, however, nose-to-nose contact takes on a very different role.

In bats, for example, similar behaviours appear to function as greeting rituals and help reinforce social bonds when individuals reunite.

In pigs, nose-to-nose contact is part of a broader repertoire of “social nosing” behaviours. These interactions are associated with reduced aggression and even improved growth rates in piglets—suggesting a link between tactile social contact and physiological benefits.

Here, the behaviour is not just about gathering information—it is also about maintaining relationships.

In other words, something that may begin as a sensory mechanism could, over evolutionary time, become a social tool.

When contact becomes control

The story becomes even more intriguing in eusocial species like the naked mole-rat.

In these animals, nose-to-nose contact is part of a behaviour known as “shoving,” where dominant individuals—particularly the breeding female—physically push subordinates.

This behaviour plays a role in maintaining the colony’s social structure, including suppressing reproduction in non-breeding individuals.

What looks like a simple face-to-face interaction is, in this case, tied to power, hierarchy, and reproductive control.

It’s a striking example of how a behaviour can be repurposed—what evolutionary biologists call exaptation—from one function (information exchange) to something entirely different (dominance enforcement).

A continuum of meaning

Taken together, these examples suggest that nose-to-nose contact exists along a continuum depending on the level of social organisation:

  • In solitary species: primarily incidental and sensory
  • In social species: affiliative and communicative
  • In eusocial species: regulatory and hierarchical

The behaviour itself remains broadly similar. But its meaning—and its evolutionary function—appears to shift depending on the social and ecological context.

Why this matters

At first glance, studying nose-to-nose contact might seem like a niche curiosity.

But it highlights something much broader.

Behaviour is not fixed. It is flexible, context-dependent, and shaped by both evolutionary history and current social environments.

The same physical action can mean entirely different things depending on who is doing it—and why.

Sophie Lund Rasmussen 2026. Exploring nose-to-nose contact in mammals. Evolution and Human Behavior, Volume 47, Issue 1, 2026, 106809.

What the replication of experiments does and doesn’t achieve

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– by Stuart West & Max Burton-Chellew

Replication or repeating of experiments is a key part of the scientific methodology. It increases your trust in that result. It shows that the result was not just due to some unnoticed bias or a particular setup. This helps to filter out false positives and expose questionable research practices. That is great.

Suppose, however, that you had developed a hypothesis for a result. In that case, repeating the same experiment might not increase your confidence in that hypothesis. If your aim is hypothesis testing then it can be more useful to alter the experiment, so that you can test between competing hypotheses or make a strong attempt to falsify a hypothesis.

Our paper was about what happens if these two points get confused. This could happen anywhere, but we illustrate the potential problem with the literature on public goods games.

The public goods game is an economic experiment designed to investigate the tension between an individual’s selfish interest and the interest of the group. Individuals can contribute money to a group fund. The group fund is multiplied by a factor and then divided between players. Crucially, the amount it is multiplied means that everyone gets back less from their contribution than they initially contributed. Consequently, while everyone would do best if everyone contributed maximally, individuals maximise their personal income by not contributing.

But when people play the public goods game, they do contribute. On average, individuals contribute a significant amount. If they play the game multiple times they contribute less, but they keep contributing. This is an incredibly strong result – the experiment has been repeated >100 times. The common conclusion is that because individuals contribute >0%, this shows that humans have ‘prosocial preferences’ which make them cooperate even when it is not in their best interest.

Can you see a potential problem with this conclusion? Individuals would only appear to behave as if they are trying to maximise their personal gain by contributing nothing (0%). Any other amount (>0%) can be argued to reflect pro-social preferences. And it is possible to come up with a huge number of alternative hypotheses for why individuals might contribute >0% (see figure above). ‘Pro-social’ preferences is a hypothesis not an unavoidable conclusion. Alternative hypotheses include, but are not limited to:

  • Individuals are prone to playing as if it was the real world, where there would be repeated interactions, and hence the opportunity for reciprocal helping.
  • Individuals might consider extreme strategies like 0 or 100% as risky.
  • Individuals might start a bit confused and want to use the game to learn how to best maximise their gain.
  • Individuals might want to explore the options available.

So, while repeating the basic public goods game experiment was great for proving the robustness of the initial result, it doesn’t help distinguish between competing hypotheses. To do that, you need to adjust your experiment. You could play the game in a way that removes the potential concern for others. For example, by making individuals play with computers or by not letting them know about the game they are playing (contributions are to a ‘black box’). Or you could change the game so that the best selfish option is to contribute >0%. Or could analyse individual behaviour and see what makes them alter their contribition. And so on.

Another way of thinking about this issue is that we need to get to the right answer by as rigorous a scientific method as possible. This can involve actively developing different controls and null hypotheses. We need to work hard to try to falsify hypotheses and test competing hypotheses.

That is our main point, and you can stop here. If you want to know the gory details from public goods games, how different controls can be developed, and how to test competing hypotheses then go and read our paper. You might also be wondering what would happen if this approach overturned the accepted conclusions. No spoilers, but there is an obvious comparison to a folktale by Hans Christian Anderson: The Emperor’s New Clothes.

Stuart A. West & Maxwell N. Burton-Chellew. (2026). Replication of experiments and the canonisation of incorrect conclusions. Evolution & Human Behavior, 46, 106749.

HBES 2026: Registration is now open (and on-campus accommodation requests are live)

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Dear HBES colleagues,

Below find important information for the HBES conference:

Registration: The registration for the 2026 meeting in Rabat, Morocco, is now open! Please visit the website for information regarding registration, or directly access the registration form. The early bird period will conclude on the 29th of March 2026. Online attendance is possible. If you wish to attend but not present at the CES conference, you can do so at a fixed discounted fee (use the HBES registration form to do so). You can also buy up to 2 tickets for the conference gala dinner, which will take place at the beautiful Rabat Story Hotel – Le Carousel (shuttle from campus included) on the evening of May 16th. Also available are two excursions to Roman ruins–the Chellah in Rabat and the Volubilis ruins closer to Meknès (both UNESCO World Heritage Sites)–planned for May 14th, to which you can also register (transportation and guide included).

Accommodation: The conference is hosted on the Rabat (Salé) campus of the UM6P. The campus offers a range of accommodation options, including the campus hotel and student residences. Prices vary based on the chosen option. Student residences are highly recommended for student participants as they are very cheap. Both are within walking distance of the event venue (approximately 3 minutes). Please note that children, while admitted on campus, are not allowed to reside in the on-campus accommodations. You can book your on-campus accommodation with this form (subject to availability).

Off-campus accommodations are available (see the website for suggestions). A regular shuttle service will pick participants near the Onomo Hotel downtown Rabat (in the Hassan neighbourhood: location here). The stop is also close to a tramline linking with hotels located in Agdal (such as the Marriott or First Suites hotel; about 10 minutes). An additional shuttle service may be provided based on the preferred location of the participants. Please note that the shuttle service is located about 20-30-minute walk uphill if you choose to reside in the Old Medina.

We are also issuing an additional call for Special Activities (e.g., workshops, training sessions, roundtables, networking events, interest-group meetups, and other community-building programming). If you would like to propose a Special Activity, please review the guidelines below and submit a proposal by email (to: HBES2026@um6p.ma). Submissions are due March 15th.

Childcare services: A free childcare center will be organised for the conference, for children from 11 months to 6 years of age. To book a space contact the organizers directly at HBES2026@um6p.ma by March 16th 2026. A discreet changing and breastfeeding space will also be provided (no booking required).

Call for activities proposals: You are invited to submit proposals for two activities to be held during the conference. All activity proposals and further questions should be sent to HBES2026@um6p.ma More details on Special Activities (including formats, expectations, and submission instructions) are included below and available at this link.

Warmly,

Zach Garfield, Ed Seabright, Sarah Alami, Mathieu Charbonneau, HBES 2026 Organizing Committee
Conference website

HBES2026 – Call for activity proposals

You are invited to submit proposals for two activities to be held during the upcoming HBES 2026 conference:

1.⁠ ⁠Lunchtime Panel Discussion

We invite proposals for a panel discussion (about 90 minutes) to be held during lunch, tentatively on the final day of the conference (May 16th). This panel should address an important topic for the discipline that is not strictly scientific but highly relevant, such as issues of representation and inclusion, ethics or equity in the field, history of the field, and broader issues shaping disciplinary culture. Proposals will be reviewed, and only two panel submissions will be selected for inclusion in the program.

Deadline: March 15th, 2026

2.⁠ ⁠Lunch Across Societies – Joint with CES

Held on the joint/overlapping day with CES (May 13th), Lunch Across Societiesoffers an informal space for small-group scholarly exchange aimed at fostering cross-societal dialogue and intellectual exchange in an informal setting. We welcome proposals for brown-bag–style interactive sessions (about 90 minutes), including methods clinics, special-interest or thematic discussions, discussions aimed at supporting junior researchers in their networking and professional development, or any other community-building discussions. Proposals will be reviewed, and a limited number of activities will be selected.

Deadline: March 15th, 2026

Submission Guidelines for 1 and 2 

Please include a short description (max 250 words) of your proposed activity or panel, outlining the following:

  • ⁠Format and topic
  • ⁠Intended audience and relevance
  • ⁠Any logistical needs

All activity proposals, video submissions, and further questions should be sent to HBES2026@um6p.ma. Please include your name and HBES2026 – Call for activities subject line.

Whom Should We Help? People Track Shared Fate to Solve Cooperation Dilemmas

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– by Diego Guevara Beltran

English

Imagine you live in a small community where food is often scarce; storms, droughts, pests, and fires can destroy crops, disease and injuries can keep you from working, and help is often the difference between getting by and going hungry. Every day, you face decisions about cooperation: Whom should I help? How much should I give? And who will help me when I need it? These are not abstract moral questions. They are practical problems that humans have faced throughout evolutionary history. And, they raise a fundamental question about evolution and human behavior: how do people decide whom to help when cooperation is costly and resources are limited? Two long-standing answers are kinship and reciprocity. But these explanations leave some important things unresolved. People often cooperate with non-kin, even when reciprocity is uncertain. Not only that, but in natural fertility populations, people often have more available kin (e.g., cousins, siblings, in-laws) than they could realistically afford to cooperate with. So, what psychological mechanisms allow people to flexibly navigate these partner-choice dilemmas? Drawing from biological markets and fitness interdependence theory, my colleagues and I argue that a key part of the answer lies in how people perceive shared fate.

Shared fate is the extent to which people believe that another person’s outcomes—good or bad—will affect their own. If your sibling falls ill, that may directly affect your workload, your food security, your coalitional strength, or your childcare needs. If your fishing partner succeeds, you may eat better too. In contrast, if an acquaintance struggles, their misfortune may have little consequence for you. From an evolutionary perspective, shared fate is a psychological estimate of fitness interdependence—the degree to which two individuals’ survival and reproduction are yoked. The central idea is this: people should be more willing to help those with whom they share positive fitness stake. But where do these perceptions come from, and what cues do people use to infer shared fate?

To address this question, I conducted fieldwork among the Mayangna, an indigenous small-scale society in northern Nicaragua. The Mayangna rely primarily on horticulture, subsidized by fishing, domestic animals, limited hunting, and sparse or seasonal wage labor. For the Mayangna, as is the case for many subsistence societies, recurrent risks such as food scarcity, illness, and disasters are part of everyday life. Absent wage-labor security or institutional support, cooperation is often the best available insurance against life’s many challenges. We interviewed 146 adults and asked them about their relationships with three types of people: an acquaintance, a cousin, and a sibling. For each relationship, we measured: (1) Ten sources of interdependence, such as relatedness, childhood co-residence, eating together, farming, hunting or fishing, labor sharing (i.e., household construction), shared religion, and experiencing disasters (i.e., floods/hurricanes) together; (2) Perceived shared fate, measured with items like “What is good for [target] is good for me” and “When [target] succeeds, I feel good”; and (3) Cooperation across seven fitness-relevant domains, including giving meat or fish, sharing crops, cooking or preparing meals, helping children, helping with household construction tasks, assisting after disasters, and helping someone harmed by outsiders.

We then tried to address a straightforward question: which sources of interdependence shape perceptions of shared fate, and do those perceptions guide cooperation? As you might suspect, not all interdependence cues are made equal. Most sources of interdependence were correlated with higher shared fate between participants. But, when we examined which cues were most diagnostic across relationships within participants, three stood out: relatedness, commensality (regularly eating together), and shared subsistence activities (i.e., planting/harvesting, and hunting or fishing). These are not arbitrary cues. They are attributes or activities that directly tie people’s outcomes together. Kinship links long-term fitness interests; while eating, farming, and foraging together not only allow people to pool risks, but such activities may also communicate to partners that we value their welfare above others. Importantly, other plausible cues—such as childhood co-residence or sharing the same religion—were not associated with shared fate once the core sources were accounted for. This suggests that shared fate is not simply about tracking social closeness or group affiliation per se. Shared fate is about tracking fitness-relevant cues of interdependence.

Perceived shared fate, in turn, was strongly associated with cooperation. People were more likely to help those with whom they perceived higher shared fate across every domain we measured—from sharing food to helping after floods. What’s more, shared fate statistically mediated the association between relatedness and helping. This suggests that shared fate is a key psychological mechanism by which kinship structures much of the cooperation observed within Mayangna communities—and perhaps across other human societies too. Finally, we wanted to test whether shared fate was associated with actual costly behavior, not just self-reports. We ran a follow-up study with a subset of participants, and we gave them a real choice: keep money for themselves or use it to buy rice for a specific partner. Shared fate was strongly associated with choosing to give up money to help someone else.

Although one interpretation of this work is that our findings simply reaffirm the importance of kinship for cooperation, we argue that such conclusion would be too narrow. The broader implication is that humans appear to possess a flexible psychological system for estimating cues of fitness interdependence, one that integrates multiple cues according to ecologically relevant affordances. In societies where cooperation is largely structured by kinship, as is the case for the Mayangna, shared fate should track kinship closely. In societies where fitness depends on cooperation with non-kin—such as friends, neighbors, or labor/exchange partners—shared fate should track such corresponding cues, including a history of shared labor, risk pooling, or even cooperation itself.

In sum, perceived shared fate may offer a simple solution to partner choice dilemmas: help those whose welfare is linked to yours. Following this heuristic allows individuals to mitigate opportunity costs, protect themselves from the costs of defection, and reap the rewards of cooperation. Understanding how people come to perceive shared fate with others could help us understand not only cooperation in small-scale societies, but also friendship, social support, and collective action in response to larger scale disasters. When people feel that their futures are intertwined, cooperation follows. When that sense of shared fate erodes, so too does willingness to help. Understanding shared fate could be as relevant for understanding how people in modern nations deal with the shadow of disasters (e.g., climate change, intergroup conflict) as it is for small-scale societies past and present.

Spanish

¿A quién deberíamos ayudar? Las personas monitorean el destino compartido para resolver dilemas de cooperación

Imagina que vives en una comunidad donde los alimentos suelen ser escasos; tormentas, sequías, plagas e incendios pueden destruir las cosechas; las enfermedades y las lesiones pueden impedir que trabajes; y la ayuda suele marcar la diferencia entre salir adelante o pasar hambre. Todos los días enfrentas decisiones sobre la cooperación: ¿a quién debería ayudar? ¿Cuánto debería dar? ¿Y quién me ayudará cuando yo lo necesite? Estas no son preguntas morales abstractas. Son problemas prácticos que los seres humanos han enfrentado a lo largo de la historia evolutiva. Y plantean una pregunta fundamental sobre la evolución y el comportamiento humano: ¿cómo deciden las personas a quién ayudar cuando cooperar es costoso y los recursos son limitados? Dos respuestas clásicas son el parentesco y la reciprocidad. Pero estas explicaciones dejan asuntos importantes sin resolver. Las personas a menudo cooperan con personas nada aparentadas, incluso cuando la reciprocidad es incierta. Además, en poblaciones de fertilidad natural, las personas suelen tener más parientes disponibles (por ejemplo, primos, hermanos, cuñados) de los que podrían permitirse ayudar de manera practica o realista. Entonces, ¿qué mecanismos psicológicos permiten a las personas navegar de forma flexible estos dilemas sociales? A partir de los mercados biológicos y de la teoría de la interdependencia de aptitud (fitness), mis colegas y yo sostenemos que una parte clave de la respuesta reside en cómo las personas perciben el destino compartido.

El destino compartido es el grado en que las personas creen que los resultados de otra persona —buenos o malos— afectarán los propios. Si tu hermano se enferma, eso puede afectar directamente tu carga de trabajo, tu seguridad alimentaria, tu fortaleza de grupo o tus necesidades de cuidado infantil. Si tu compañero de pesca tiene éxito, tú también podrías comer mejor. En contraste, si un conocido pasa por dificultades, su infortunio puede tener pocas consecuencias para ti. Desde una perspectiva evolutiva, el destino compartido es una estimación psicológica de la interdependencia de aptitud: el grado en que la supervivencia y la reproducción de dos individuos están ligadas. La idea central es simple: las personas deberían estar más dispuestas a ayudar a quienes comparten con ellas una apuesta positiva de aptitud. Pero ¿de dónde provienen estas percepciones y qué señales utilizan las personas para inferir el destino compartido?

Para abordar esta pregunta, realicé trabajo de campo entre los Mayangna, una sociedad indígena de pequeña escala en el norte de Nicaragua. Los Mayangna dependen principalmente de la horticultura, complementada por la pesca, animales domésticos, caza limitada y trabajos asalariados escasos o estacionales. Para los Mayangna, como para muchas sociedades de subsistencia, riesgos recurrentes como la escasez de alimentos, la enfermedad y los desastres forman parte de la vida cotidiana. En ausencia de seguridad laboral asalariada o de apoyo institucional, la cooperación suele ser la mejor póliza de seguro disponible frente a los múltiples desafíos de la vida. Entrevistamos a 146 adultos y les preguntamos sobre sus relaciones con tres tipos de personas: un conocido, un primo y un hermano. Para cada relación medimos: (1) diez fuentes de interdependencia, como el parentesco, la co-residencia durante la infancia, comer juntos, cultivar, cazar o pescar, compartir trabajo (es decir, construcción del hogar), religión compartida y experimentar desastres juntos (es decir, inundaciones y huracanes); (2) el destino compartido percibido, medido con ítems como “Lo que es bueno para [esta persona] es bueno para mí” y “Cuando [esta persona] tiene éxito, me siento bien”; y (3) la cooperación en siete dominios relevantes para la aptitud, incluyendo dar carne o pescado, compartir cosechas, cocinar o preparar alimentos, ayudar con el cuidado de los niños, colaborar en tareas de construcción del hogar, asistir después de desastres y ayudar a alguien perjudicado por personas externas.

Luego abordamos una pregunta directa: ¿qué fuentes de interdependencia de aptitud moldean las percepciones de destino compartido, y esas percepciones guían la cooperación? Como cabría esperar, no todas las señales de interdependencia son iguales. La mayoría de las fuentes de interdependencia se correlacionaron con un mayor destino compartido entre participantes (es decir, aquellos que mencionaron altas fuentes de interdependencia en general mencionaron percepciones de destino compartido más alto). Sin embargo, al examinar cuáles señales eran más diagnósticas a través de las relaciones dentro de cada participante, destacaron tres: el parentesco, la comensalía (comer juntos de manera regular) y las actividades de subsistencia compartidas (es decir, sembrar y cosechar, y cazar o pescar). Estas no son señales arbitrarias. Son atributos o actividades que vinculan directamente los resultados de las personas. El parentesco conecta intereses de aptitud a largo plazo; mientras que comer, cultivar y recolectar juntos no solo permite compartir riesgos, sino que también puede comunicar a nuestros socios que valoramos su bienestar por encima del de otros. De manera importante, otras señales plausibles —como la co-residencia en la infancia o compartir la misma religión— no se asociaron con el destino compartido una vez que se tuvieron en cuenta las fuentes centrales. Esto sugiere que el destino compartido no se trata simplemente de monitorear la cercanía social o la afiliación grupal per se. Se trata de monitorear señales de interdependencia relevantes para la aptitud.

El destino compartido percibido, a su vez, se asoció fuertemente con la cooperación. Las personas fueron más propensas a ayudar a quienes percibían con mayor destino compartido en todos los dominios que medimos, desde compartir alimentos hasta ayudar después de inundaciones. Además, el destino compartido medió estadísticamente la asociación entre parentesco y la ayuda. Esto sugiere que el destino compartido es un mecanismo psicológico clave mediante el cual el parentesco estructura gran parte de la cooperación observada en las comunidades Mayangna —y quizás también en otras sociedades humanas. Finalmente, quisimos probar si el destino compartido se asociaba con conductas costosas reales, no solo con autoinformes. Realizamos un estudio de seguimiento con un subconjunto de participantes y les dimos una elección real: quedarse con el dinero o usarlo para comprar arroz para una persona en específico. El destino compartido se asoció fuertemente con la decisión de renunciar al dinero para ayudar a la otra persona.

Aunque una interpretación de este trabajo es que nuestros hallazgos simplemente reafirman la importancia del parentesco para la cooperación, sostenemos que esa conclusión sería demasiado estrecha. La implicación más amplia es que los humanos parecen poseer un sistema psicológico flexible para estimar señales de interdependencia de aptitud, que integra múltiples señales de acuerdo con las oportunidades ecológicamente relevantes. En sociedades donde la cooperación está ampliamente estructurada por el parentesco, como ocurre entre los Mayangna, el destino compartido debería seguir de cerca al parentesco. En sociedades donde la aptitud depende de la cooperación con personas poco o nada aparentadas —como amigos, vecinos, o socios de trabajo o de intercambio— el destino compartido debería monitorear señales correspondientes, incluyendo una historia de trabajo compartido, la puesta en común de riesgos o incluso la cooperación misma.

En suma, el destino compartido percibido puede ofrecer una solución simple a los dilemas de cooperación: ayudar a quienes tienen su bienestar ligado al propio. Seguir esta heurística permite a las personas mitigar costos de oportunidad, protegerse de los costos de la deserción y obtener los beneficios de la cooperación. Comprender cómo las personas llegan a percibir el destino compartido con otros puede ayudarnos a entender no solo la cooperación en sociedades de pequeña escala, sino también la amistad, el apoyo social y la acción colectiva frente a desastres de mayor escala. Cuando las personas sienten que sus futuros están entrelazados, la cooperación sigue. Cuando ese sentido de destino compartido se erosiona, también lo hace la disposición a ayudar. Comprender el destino compartido puede ser tan relevante para entender cómo las personas en sociedades modernas enfrentan la sombra de los desastres (por ejemplo, el cambio climático o los conflictos intergrupales) como para las sociedades de pequeña escala del pasado y del presente.

Link to article

Diego Guevara Beltran, Jessica D. Ayers, Lee Cronk, Daniel P. Balliet, Jeremy Koster, & Athena Aktipis. (2026). Sources of fitness interdependence associated with shared fate and cooperation in a small-scale horticultural society. Evolution & Human Behavior, 47, 106802.