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.

– 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.

– 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.