crowd of participants in speed-dating

Funny How? Humour as an Evolved Trait

– by Henry Wainwright

Humour is an everyday part of our lives and is present in virtually all human cultures, seemingly both past and present; the oldest known surviving joke being from Bronze Age Sumer, circa 1900 B.C. And while what we find funny is likely culturally and socially influenced, the fact that we all have a sense of humour, irrespective of culture, strongly suggests that humour evolved for some purpose.

One among many evolutionary explanations is that humour may have helped our ancestors to attract a mate. Indeed, individuals today consistently report a preference for humour in a romantic partner. However, it remains unclear why, in an ultimate sense, humour is considered an attractive quality. Humour is enjoyable, of course – but there is nothing inherently enjoyable or attractive about what we describe as funny. The question becomes, why did we evolve to find certain things funny and to be attracted to funny individuals?

The ‘fitness indicator hypothesis’ argues that humour aided ancestral courtship because being funny signals underlying genetic quality. Specifically, the idea is that funniness requires mental performance (e.g. speed, intelligence, creativity), which in turn requires a high-functioning brain, which in turn requires a low load of genetic mutations. Therefore, both being funny and being attracted to funny people are evolutionarily favoured because offspring of these couplings will inherit lower mutation loads and pass on their parents’ genes more effectively.

We tested predictions from the fitness indicator hypothesis by having participants – undergraduate students from the University of Queensland – report their preferences for humour in a romantic partner (i.e. their stated preferences) before engaging in a multiple unscripted, three-minute speed dates with each other, for a total of 860 unique dates. After each date, participants rated their partner on several characteristics including their funniness, their  humour receptivity (they found me funny), and their overall attractiveness.

Audio from these interactions were also surreptitiously recorded for a subset of 563 dates, which enabled the use of an additional, objective measure of humour, in the form of laughter frequency. From there we tested the central predictions of the fitness indicator hypothesis: that funniness and humour receptivity are attractive traits. We were also interested in additional predictions of the hypothesis, namely, that in accordance with parental investment theory, there should be a sex differences in how men and women respond to humour. That is, men should be attracted to humour receptivity in a partner more than women, whereas women, more so than men, should value funniness in a partner.

Indeed, results from stated preferences were largely consistent with these predicted sex differences. However, relying on stated preferences alone is problematic because doing so assumes that participants have sufficient, bias free insight into their own preferences. In practice, stated preferences often fail to predict individuals’ evaluations of potential partners (i.e. their revealed preferences). Therefore, we continued our investigation by looking at revealed preferences using laughter as well as ratings of humour .

We began by looking at how strongly participants’ ratings of their partners’ funniness or humour receptivity correlated with their ratings of the partners’ overall attractiveness. This allowed us to first check the basic premise of the fitness indicator hypothesis: that funniness is actually attractive. Consistent with this premise, partners who were rated as funnier were also rated as having greater overall attractiveness. Notably, the same was not found for humour receptivity – partners rated as more receptive were rated no more or less attractive overall. More damaging for the fitness indicator hypothesis, though, is that the predicted sex differences were not observed at all: the associations of both funniness and humour receptivity with overall attractiveness were similar in men and women.

Using ratings as a sole assessor of revealed preferences can be troublesome, as post-interaction ratings are possibly subject to a halo effect, whereby participants might rate a partner as funnier simply because they were more physically attractive, for instance. Therefore, we examined revealed preferences using laughter as a real-time, behavioural measure of both funniness and humour receptivity. After first establishing that at-partner-laughter (i.e. participant laughter following something their partner said) was positively associated with ratings of funniness, thus partially validating laughter as a measure of humour, we found that neither funniness nor humour receptivity, as measured by laughter, predicted ratings of overall attractiveness. Furthermore, using laughter, we found no evidence that men value humour receptivity in a speed-date partner more than women do, or that women value funniness in a speed-date partner more than men do.

In summary, we found that while stated preferences largely supported the sex differences predicted by the fitness indicator hypothesis, results from revealed preferences, which are taken as more valid than stated preferences, did not support these predicted sex differences and offered only mixed support for the central premise of the hypothesis, that funniness is attractive.

Overall, our results call into question not only the fitness indicator hypothesis, but also (or alternatively) the degree to which parental investment theory can be applied to sex differences in humans’ preferences for fitness indicators. The absence of significant sex differences in revealed preferences alone does not necessarily exclude humour as a fitness indicator; instead, it may be that the degree to which parental investment theory predicts sex differences in human fitness indicators has been overestimated. Humans exhibit mutual mate choice, and as a result, fitness indictors are still expected to evolve, but not necessarily with large (or any) sex differences. So the possibility remains that humour may be a fitness indicator, but men and women differ little, if at all, in their attraction to it. The current study is partially consistent with this possibility, as there is evidence that both funniness was a desirable trait to both sexes similarly. However, further investigation, especially into the role that humour plays in romantic attraction over longer periods of acquaintance, is needed to fully investigate this possibility, as well as to comprehensively test the fitness indicator hypothesis.

Read the original article: Wainwright, H.M., Zhao, A.A.Z., Sidari, M.J., Lee, A.J., Roberts, N., Makras, T., & Zietsch, B.P. (2024). Laughter and ratings of funniness in speed-dating do not support the fitness indicator hypothesis of humour. Evolution and Human Behavior, 45(1), 75-81.

Connections beyond blood: chosen kin are integral to human social life

– by Ollie Shannon & Anne Pisor

The Vatican made it official: transgender individuals can now serve as godparents.

But what is a godparent and why are godparents important? Ultimately, answering this question requires us to think about the evolution of human social life – and the importance of chosen kin.

Humans raise children cooperatively, with alloparents – people other than the parents – usually involved. Born helpless and with long childhoods, our kids need all the help they can get.

Evolutionary social scientists have traditionally focused on biological kin as helpers, much as bio kin are the primary helpers in other cooperative breeders like crows and meerkats. But the Vatican’s declaration reminds us that in humans, the question of who helps is more complicated.

Choosing kin

Humans have a diversity of non-kin alloparents – a rich tapestry of social relationships and reciprocal obligations. Non-bio kin can be especially involved when bio kin aren’t available to help, like in communities with high residential mobility or in the Queer community, when bio kin sometimes aren’t interested in helping their Queer kids. In marginalized communities facing systematic challenges such as poverty or discrimination, individuals may face limitations in the support they can offer due to these systemic factors and may rely on a combination of bio-kin and non-kin alloparents to help everybody’s children thrive.

When humans lack needed family support, we often create the family we need. In the Black community, for example, churches and religious institutions offer a sense of community during tough times and joyful occasions. The use of kinship terms such as “brother” and “sister” in a religious context affirms and strengthens these relationships. For this reason, non-bio alloparents are often called chosen kin or, using an older term from anthropology, fictive kin.

Compadres, padrinos, and ahijados

Godparents are chosen or bio kin who commit to being a child’s alloparent, usually through a ritual – by being present at a birth, for example, supporting a child’s graduation party, or being present at a child’s baptism. In Latin America, where godparenthood (compadrazgo) is widespread in the Catholic church, the choice of godparent is often guided by a mix of considerations, including the social standing of the godparent and their ability to provide help and resources.

In rural Bolivia, the focus of our recent paper in Evolution & Human Behavior, the support and resources godparents provide is sometimes day-to-day, like after-school care, but can also be rare but big infusions of help. Godparents who live in the city, for example, can house an adult godchild when they go to university, provide help with bureaucracy, or send packages of things not available rurally, like cheap smartphones or other household items.

Given the importance of godparents in this context, we asked: how might godparents impact child outcomes? For example, if godparents often provide after-school care or house their grown godchildren, does this impact godchildren’s educational outcomes? Studying how and the degree to which godparents impact child outcomes across societies could unlock key insights – like the benefits of non-kin alloparental support to kids, parents, and the alloparent themselves – that are still not a common focus in the evolutionary literature.

In 2017, one of us (AP) led a research team that interviewed 148 adults about their children, including their adult children: we wanted to know not only whether their kids had godparents, but where those godparents lived, and what their kids’ educational outcomes were. Among the 210 adult children discussed, 163 had at least one godparent. However, these godparents didn’t have detectable impacts on their godchildren’s education in our statistical models – not on years of education, high school completion, or even pursuing a university degree. It didn’t matter if the godparent lived in the same community – where the godchild’s high school was located – or somewhere else, or even whether the godparent was actually bio kin who had been given godparent status.

Instead, we found that adult children with more older siblings were likely to have more years of primary and secondary education, complete high school, and pursue higher education. Older siblings are important alloparents in many contexts, with varying impacts on child outcomes – including educational attainment.

What next in the study of chosen kin as alloparents?

Our findings underscore that chosen kin may not have measurable effects in all domains of a child’s life – but, as captured by our ethnographic data, are still making things easier for parents and children alike, by providing care, resources, and even housing. Whether through quantitative or qualitative data collection, focusing on impacts on children or even on their parents, there is still much to be done in understanding why chosen kin are so prevalent in human societies.

In the rich tapestry of human sociality, the concept of chosen kinship serves as a testament to the flexible nature of human relationships. By embracing the complexity of chosen kinship, we honor the resilience and diversity of human social bonds, fostering a more inclusive and compassionate approach to human relationships.

Read the original article: Hubbard, E.B., Shannon, O., & Pisor, A.C. (2023). Non-kin alloparents and child outcomes: older siblings, but not godparents, predict educational attainment in a rural context. Evolution & Human Behavior, 44(6), 597-604.

Is the Mind a Swiss-Army Knife or a Crowbar?

Image: A vintage and somewhat unscientific map of mental functions. But how fine grained are these adaptations?

– by Thomas J. H. Morgan

From the outside, the brain is a medium sized, pinkish-grey blob. At the microscopic level, it’s a densely woven mesh of countless neurons. In between these two extremes is the brain’s functional structure – the mind, or more concretely, how those neurons are wired together to solve problems and manage behavior.

A popular metaphor for the mind is the Swiss-army knife. Like the brain, the Swiss-army knife has a large-scale external appearance (red, cigar-shaped, with silver rotating appendages) and a microscopic constitution (atoms and molecules). However, it also has a functional mid-level structure, being composed of subunits that solve particular problems – opening bottles, filing nails, driving screws, scaling fish, cutting wires, and so on.

As useful as it is, the Swiss-army knife has limitations. Screwdrivers and fish scalers aren’t much use without screws or a means to catch fish. Someone heading out into the unknown might instead prefer a kit of fewer but more widely applicable tools. Say, an axe and a crowbar. Rather being designed for specific problems, these items can be put to work in many contexts and so can handle unforeseen situations more successfully.So, what does the mind look like – a bespoke Swiss-army knife with many task-specific solutions, or an adaptable survival kit of just a few broadly applicable tools? This is the question we set out to answer. We recruited groups of participants and had them collectively complete a task. The task we chose was mate-choice copying – participants evaluated how attractive they found photos of other people, and then they saw what other participants thought and could alter their decision.

Mate-choice copying is particularly relevant to this question as it sits at the interface of two fields – evolutionary psychology, which has collected lots of data on human mate choice, and cultural evolution, which has extensively studied copying and social influence. In addition, while some prior work on mate choice copying has suggested it is managed by a mental adaptation evolved specifically for this task, other work has argued the mental system is broader and handles decision making and learning more generally.

Prior work led by Dr. Sally Street had already found that humans were equally influenced by what others thought about the attractiveness of human faces, human hands and abstract art, but we wanted to dig into the details. Studies of copying across many other contexts have documented that humans are influenced by majorities (“conformity”) as well as by successful individuals (“prestige”). We tested whether these same patterns occurred in mate-choice copying. In addition, we collected data from both men and women to see if there were gender differences in copying. Our reasoning was that the more mate-choice copying differed between genders or from copying in other contexts then the more likely it was underpinned by a mate-choice specific adaptation.

Our results showed the opposite. Participants were influenced by each other’s decisions, and analysis of the patterns in this copying found strong evidence of both conformity and prestige. In addition, there was strong evidence that both men and women copied in the same way. We thus concluded that rather than a bespoke system, mate choice-copying is underpinned by the same copying mechanisms that are active in other contexts – it’s a crowbar, not a Swiss-army knife.

There are two important points though. First, although we suggest the mind is made of general-purpose systems, these systems are still adaptations – they are just adaptations for broad classes of problems, as opposed to specific tasks. Second, even broadly applicable systems can be flexibly tuned to meet particular needs. For instance, copying is known to be adjusted according to factors like confidence and risk. Through factors like these, even broad ranging systems can be adaptively tuned for particular tasks, just like a crowbar can be applied with different amounts of force. Thus, the mind might have fewer solutions than the Swiss-army knife metaphor suggests, but its adaptive power comes from the flexible use of the tools at its disposal.

Read the original article: Foreman, M., & Morgan, T.J.H. (2024). Prestige, conformity and gender consistency support a broad-context mechanism underpinning mate-choice copying. Evolution and Human Behavior, 45(1), 58-65.

An issue of EHB

New E&HB article format: Short Reports

The official HBES journal, Evolution and Human Behavior, has created a new report format: short reports. Short reports, created in honor of John Tooby, are intended to expedite the publication of concise reports of original research. Short reports contain no more than 3000 words in the introduction, methods, results and discussion combined, an abstract of 200 words or less, and a maximum of 30 references. The introduction, only a few paragraphs in length, should state concisely the evolutionary rationale for the project (for example, the relevant selection pressure/adaptive problem and proposed behavioral/cognitive solution), a very brief description of the methods used, and specific empirical predictions. Short reports may have online-only supplements that contain full materials, supplemental tables, and details of complex methods. However, the supplement may not be used to circumvent the word count. A reviewer/reader of EHB should be able to evaluate the science of a short report solely from the main paper. Members of the Editorial Review Board and Invited Reviewers of short reports will be notified of this new format to ensure appropriate appreciation of its concise nature. Details will appear soon on the EHB website.

Take part in a commentary article on John Tooby quotes

– by Deb Lieberman, Editor-in-Chief, Evolution & Human Behavior

In honor of John Tooby (1952-2023) and his contributions to our field, members of HBES and invited guests are welcome to pick a quote(s) from any Tooby publication of any year and take up to 350 words to state its importance or its impact on science. The 350-word runway is firm, no matter how many quotes you pull. You need not include a discussion of the quote if you do not wish; you can simply include your favorite quotes or passages. Whatever the case, your all-in word limit including any quotes is a firm 350 words. This is to allow as many HBES members to contribute as possible.

FAQ:

How many submissions per scholar?
One

How many authors per submission?
One. Single author submissions only.

Can the same quote be used by multiple contributors?
Yes. Of all the sentences written, we are hoping there is a wealth of options. However, we also know that people will have different interpretations and comments on similar quotes. The editorial team will organize submissions.

How many references are allowed?
The only references allowed will be for the quote(s) used.

What is the word limit?
350 words. All in. Firm.

How do I submit?
Complete the form using the Qualtrics link or QR code below: https://umiami.qualtrics.com/jfe/form/SV_bgA7sgv20cJsvmm

QR code for submissions

Will the submissions be reviewed?
Yes, by members of the Editorial Board. HBES membership will be verified. Submissions from non-HBES members (or individuals who have not been personally invited by the Editor) will be rejected. If you’d like to renew your HBES membership prior to submission, visit: https://www.hbes.com/membership-join/

Where can I find all of John Tooby’s publications?
Here is a link to the Center for Evolutionary Psychology Publication list, where you can find most of John’s publications. (https://www.cep.ucsb.edu/publication/)

When are submissions due?
Submissions are due by March 31st and notification of acceptance will be rolling. The link for submissions will be disabled after this date.

When will the tribute be published?
The editorial team will collect and compile the submissions, with the aim of publishing the collection as a single on-line article in the third or fourth issue of 2024. Details will be sent to contributors.

Deb Lieberman
Editor-in-Chief, EHB

Dates, deadlines, & info about HBES 2024 (Aarhus, Denmark)

We are fast approaching the 35th Annual Meeting of the Human Behavior & Evolution Society in Aarhus, Denmark! It will be held at Aarhus University from May 22-25, 2024. Here are some important dates to know about HBES 2024:

  • Abstract submission deadline: Feb 1st
  • Final abstract acceptance confirmations: March 1st
  • Last day for Early Registration: March 31st
  • Regular Registration begins: April 1st
  • Childcare registration deadline: April 15th
  • Regular Registration ends: May 21st
  • Late Registration begins: May 22nd
  • Conference dates: May 22-25

We have an exciting lineup of plenaries: Brian Nosek will give the keynote, and we will have plenaries by Dorsa Amir, Lisa Feldman Barrett, Nicolas Baumard, Judith Maria Burkart, Joseph Carroll, Jaimie Krems, and Manvir Singh.

Bookmark the conference website for updates and the most recent information.

Looking forward to seeing you in Aarhus!

Tsimane woman gardening while younger females watch

Cultural transmission: Who learns what from whom? When, how, and why?

– by Eric Schniter, Michael Gurven, & Hillard Kaplan

Humans depend on culturally transmitted knowledge and skills crucial for their survival. But how is essential culture transmitted?

In economically modern human societies, most youngsters are formally educated alongside their similar-aged peers by unrelated teachers from an older generation. Adults in modern societies often develop into specialists, learning novel specialized skills from their coworkers and prestigious peers. But is this pattern of “horizontal” and “oblique” transmission from unrelated others the most fundamental mode of human culture transmission?

Evidence from subsistence groups like the Tsimane suggest that the patterns of cultural transmission, schooling, and skill development seen in economically modern society are not universal to all humans and were likely uncommon among our ancestors who relied on multi-generational broad social structures of kin-based exchange.

In our recent study in Evolution & Human Behavior, we brought a life history approach to the study of transmission vectors that considers how changes in embodied capital, combined with gender and relatedness, affect the costs and benefits to both the influencer and the learner. We emphasize the investments made in knowledge and skill across the human lifespan, and the returns on these investments at different ages that manifest in the array of competencies we see in a cross-section of society. We adapt the vector framework introduced by Luigi Cavalli-Sforza and Marcus Feldman to describe vertical, oblique, and horizontal cultural transmission relationships (see Figure 1).

Figure 1. Schematic representation of the intra- and inter-generational cultural transmission vectors, both related and unrelated that potentially influence receivers’ culture acquisition. Our cultural transmission study focuses on the relationships in bold fonts and colors.

So, what did we find? When do people learn, from whom, and how?

Our study focusing on 421 adult Tsimane forager-farmers native to Bolivia sheds light on how essential skills and specific domains of knowledge find their way from person to person and from one generation to the next. We examined the transmission vectors and styles of influence behind Tsimane people’s acquisition of 92 skills, ranging from those involving foraging, domestic chores, crafts and tool manufacture, childcare, music, and more. This transitioning community, living at the intersection of traditional foraging and farming practices and the rapidly changing demands of market integration, provides a unique lens to understand the vectors and influences driving cultural transmission.

We used a survey approach to gather knowledge about the skills that people had, their proficiency with those skills, and their reports of who influenced their skill acquisition by teaching, correction, helpful example, encouragement, or discouragement. Tsimane people report acquiring basic competency with most skills by the end of childhood and developing their skill proficiency further throughout adulthood.

Older, same-sex relatives predominantly influence Tsimane culture transmission, and in a variety of ways. They lead by example, directly instruct, correct learner’s mistakes, and sometimes just encourage and positively reinforce behaviors. Older adults are named most for these influences, despite the greater amount of time that kids spend interacting with same-generation peers while developing proficiency with most skills.

95% of culture transmission is reported as coming from within families (87% blood relatives, 8% related by marriage) and 75% from older kin. Vertical transmission from parents is most common, followed by oblique transmission from older kin. For example, grandparents –revered for their wisdom and experience—play a crucial role in imparting difficult-to-acquire skills that demand less physical strength but more complex knowledge, such as music performance, storytelling, and crafting. In contrast, peers of the same generation tend to positively influence the acquisition of modern, market-oriented skills, like finding wage labor opportunities and using machines for farming.

While similar-aged peers facilitate the acquisition of modern skills, they are reported to be the least helpful when it comes to positively influencing traditional skill acquisition. Unlike older kin, peers of the same generation are more likely to be competitors during the skill acquisition process, explaining why they are reported to be the mostly likely contributors of discouragement, a negative influence intended to inhibit skill acquisition.

We examined a diverse set of essential Tsimane skills and types of knowledge that has been conserved for untold generations, underscoring the important role of older adults and the multi-generational support of youngsters and young adults. This dominant pattern of kin-biased cultural transmission from older to younger generations mirrors the Tsimane pattern of kin-biased net food transfers between generations and within extended families (see here and here).

In subsistence societies, essential skills continue to develop for decades after they have been acquired (e.g., see here), forming older adults into “banks” of accumulated cultural solutions and practical knowledge (e.g., see here, and here). Our findings are consistent with the view that older-to-younger cultural transmission is the result of selection for a long lifespan favoring peak abilities for information retrieval and transmission to younger kin at late ages.

Generations of cultural isolation likely helped the Tsimane conserve their multigenerational system of cooperation and downward traditional culture transmission. However with rapid modernization, the current and future generations will face new challenges. Older adults’ contributions to their forager-farmer economy have been possible because of their comparative advantages and accumulated experience that comes with age. As transitioning societies increasingly value novel skillsets, and as younger generations develop comparatively greater proficiency and productivity with these modern skills, the opportunities for positive cultural influence and transfers from younger to older generations will grow. These results suggest that successful aging among adults, in both Tsimane and economically modern societies, will hinge on both upward inter-generational flows of knowledge and resources, and younger generations maintaining an appreciation for older adults’ roles as trusty helpers, educators, and experts of cultural traditions.

Read the original paper: Schniter, E., Kaplan, H. S., & Gurven, M. (2023). Cultural transmission vectors of essential knowledge and skills among Tsimane forager-farmers. Evolution and Human Behavior.

Culture and Context Matter when Thinking about the Phenomena of Ownership

– by Ulises Espinoza

The evolutionary social sciences have long sought to comprehend human commonalities. Among these inquiries, a central focus revolves around identifying the traits that collectively compose the so-called “human nature” of our species, in both their psychological and behavioral dimensions. It prompts us to ponder whether certain traits, transcending cultural boundaries, are universally present during early childhood. This often involves the establishing of connections between these putative universal or prevalent traits and their evolutionary origins, shaped by the forces of natural selection in the distant past. One particularly intriguing arena of exploration is in the domain of ownership, and the conceivable underlying psychological and cultural norms and regulations that govern it.

It’s likely that all humans have the capacity to recognize ownership in themselves and others. However, it is an open question whether there is a specific, species-typical human psychology of ownership, and whether that psychology contains particular rules or principles. In principle, it is possible that ownership is a purely cultural phenomenon. But there may also be evolutionary roots to how we conceptualize ownership and to the domains to which ownership is extended. In a recent paper, H. Clark Barrett and I delve into the intriguing question of whether ownership has possible universal features. We explore a set of norms called “first mover norms,” which suggest that the person who takes the initial action or makes the greatest effort towards an ownable object is socially recognized as its rightful owner. These norms can apply to various tangible and intangible items. Studies have shown that children, in primarily Western samples, tend to develop these first mover intuitions during early to middle childhood, suggesting a potential universality. Cross-cultural research has also supported these findings, although with some variations in developmental patterns. However, when examining ethnographic evidence, the picture becomes more complex. While first possessor rules exist in non-Western legal systems, many societies have diverse ownership norms. Ownership rights can be communal, partial, or subject to negotiation based on principles like kinship, sharing, stewardship, use, and need. Even in cases where first mover norms appear to apply, they often don’t confer permanent, individual ownership, as other cultural principles determine rights.

Our investigation ventured into the realm of ownership within Achuar communities, renowned for their distinctive fusion of individual autonomy and robust communal values. To shed light on the subject, we conducted experimental scenarios involving ownership claims in two culturally pertinent domains: land and hunting. To ensure cross-cultural comparability, we also included participants from the United States. Among the American participants, the notion of “first possession” held considerable sway in their judgments across various scenarios, whether related to hunting or land. Their consistent preference for the first possessor as the rightful owner aligns with the historical and cultural influences in American and European societies, where the concept of first possession has exerted a profound influence on the development of legal and cultural norms. Conversely, Achuar participants showed a less consistent bias towards first possession, depending on the context. In hunting scenarios, they recognized the person who captured a game animal as the owner, reflecting their cultural practices. However, when it came to assigning ownership of land, they prioritized factors like use and improvement over mere first possession. This reflects their belief in land stewardship and the idea that ownership is not static but earned through active use and care. These results highlight the dynamic nature of the of the use of first-mover norms, particularly concerning their role in determining actual ownership across diverse cultural contexts. Americans, and potentially Westerners more broadly, appear to lean toward the heuristic of first possession, while other cultures, exemplified by the Achuar, consider a broader spectrum of factors when adjudicating ownership. The concept of ownership is nuanced and exhibits considerable divergence on a global scale, challenging the notion of a universally shared human comprehension of this concept.

Our findings underscore the necessity of exercising caution when extrapolating from specific cultural samples to the broader global population (Barrett, 2020). This holds particularly true for various facets of human psychology, including those, like ownership, that are profoundly influenced by cultural factors. It suggests that studies conducted in the United States and Europe may possess limited applicability when seeking to generalize findings to broader populations. It prompts us to reevaluate the notion that an evolved psychology of ownership, while potentially existing in humans, may be significantly influenced by cultural distinctions and the intricate tapestry of cultural history. Our study represents a modest and preliminary exploration of ownership intuitions within Achuar communities. We believe that future research endeavors in this community, as well as in other Indigenous communities characterized by distinct ownership traditions diverging from those of European-descendant communities, hold the key to presenting a more comprehensive portrait of the variations in human ownership psychology and the commonalities that may exist across diverse human societies. Each contemporary human community serves as a valid exemplar of the myriad potential configurations of evolved human psychology, each bearing an equally extensive cultural heritage. Rather than idealize certain communities as superior or inferior exemplars of evolved human nature, evolutionary social scientists can reap significant benefits from examining the complete spectrum of contemporary human psychologies. This approach provides valuable insights into the essence of human nature, elucidating both its defining characteristics and the boundaries that demarcate it.

Read the original paper: Espinoza, U., & Barrett, H.C. (2023). Cultural and contextual variation in first mover norms of ownership: evidence from an Achuar community. Evolution & Human Behavior, 44(6), 584-596.

This article is part of the Special Issue – Dispatches from the Field Part II.

Life in Chocó, Colombia

Human intergroup relations are profoundly flexible. Our science needs to catch up.

– by Anne Pisor

Is intergroup aggression part of human nature? Or is intergroup tolerance part of human nature?

Yes and yes.

While such simple headlines make great clickbait, they oversimplify – yet both have a grain of truth. Humans are both profoundly hostile and profoundly tolerant toward out-groups. We’re profoundly flexible.

Flexible intergroup relations have deep evolutionary roots. Though chimpanzees are often thought of as hostile toward out-group members and bonobos as tolerant, there is some variation in chimpanzee intergroup relations and quite a bit of variation in bonobos. Given the range of opportunities for conflict and cooperation in humans – from defending resources and protecting ourselves, to exchanging resources and ideas – the profound flexibility of human intergroup relations shouldn’t surprise us.

Indeed, as Cody Ross and I write in a new piece in Evolution & Human Behavior, our behavior toward members of other groups is influenced by a whole pathway of things, starting with context (are resources scarce?) and individual characteristics (did my past interactions go poorly?) that affect our beliefs, attitudes, and motivations – our internal states. Context, individual characteristics, and internal states influence how we behave.

For example, take research led by Cody in rural Colombia, where indigenous Emberá and Afrocolombians live side by side – sometimes with discord, sometimes without. In one community, Emberá have more control over natural resources and there’s a history of intergroup tensions. Even though Afrocolombians are wealthier than Emberá in that community, Afrocolombians feel that intergroup tensions are high and cooperation low – and they share less money and food with Emberá households accordingly. In another community with less unequal resource control and less history of intergroup tensions, wealthy Afrocolombians share with poorer Emberá. The impact of context on our internal states and our subsequent cooperative behavior is not to be underestimated.

Capturing the profound flexibility in human intergroup relations requires methods that document it accurately. In our Evolution & Human Behavior article, Cody and I focus on a subset of intergroup relations called parochial altruism: in-group favoritism paired with out-group hostility. Variance in parochial altruism is best documented using a combination of methods, we argue, like experiments that measure who people prefer to share with, observations on who they actually share with in everyday life, and self-reported internal states.

Using just one method can generate bias. For example, as Cody has documented in Colombia, people may not reciprocate sharing in real life because they can’t afford it, but will preferentially repay real-life sharing in an experiment when researchers provide the money. In short, to triangulate reality, researchers must approach it from a variety of angles.

If intergroup behavior is so flexible in humans, why are simple headlines about it so common? One reason is that they often seem to either confirm or challenge our own internal states – “yes, of course humans are inherently violent”; “no, violence isn’t part of human nature!” Our own internal states are themselves products of our experiences and cultural contexts, among other things. Journalists know that headlines that confirm or challenge our internal states excite our emotions, making us more likely to click.

But these headlines are also common because researchers have their own internal states too, and these influence what research actually gets done. As Brian Hare and Vanessa Woods remind us in Survival of the Friendliest, research on intergroup violence ticked up after World War II: researchers wanted to understand how atrocities could be committed on such massive scales. Science can be guided by researchers’ own experiences or by history, which impact researchers’ beliefs about intergroup hostility, tolerance, and peace.

When there is a greater diversity of experiences among researchers, science is the better for it. It increases the diversity of research questions researchers ask, and having a range of research questions can better tap the range of the human experience – our flexibility in intergroup relations, for one. In turn, this data can be leveraged for policy recommendations and action – for example, what features of context, individual characteristics, and internal states have the greatest downstream influence on intergroup behavior? Which lever should we pull to intervene, reducing intergroup hostility?

As Cody and I highlight, answering these diverse questions about intergroup relations requires data that accurately reflect the diversity of human experiences – our profound flexibility. Ensuring data collection reflects research questions, triangulating across multiple types of measures, striving to ensure measures reflect reality – this will improve our understanding of human intergroup relations and the upstream factors that influence it.

War in Israel and Gaza, tensions over fossil fuels at COP28, impasses in parliaments and US Congress – these stories bring to mind humans’ profound intergroup hostility. Communities helping one another after a storm, organizations standing together on picket lines – these bring to mind humans’ profound intergroup tolerance. For researchers and non-researchers alike, our beliefs, attitudes, and motivations are affected by what’s around us and by our past experiences. When researchers bring that diversity of experiences to science, our understanding of human nature can also become more accurate – but only if researchers also get accurate measures of what humans are up to. Existing data already undercut the narrative that humans are doomed to favor in-groups and be hostile toward out-groups: the data instead reveal profound variability. Recognizing this variability can push scientists to challenge their own preconceptions about human nature and to draw upon a more diverse toolkit, improving our understanding of the flexibility of intergroup relations. The better we understand it, the better positioned we’ll be to address the pressing social issues of the 21st century.

Read the original article here: Pisor, A.C., & Ross, C. (in press). Parochial altruism: what it is and why it varies. In press at Evolution & Human Behavior.

Author’s note: the author thanks Cody Ross, Kris Smith, and Eleonora Zanetti for helpful comments on this piece. Photo credit: Karl Frost.

Unmaking egalitarianism

– By Christopher von Rueden

(Photo credit: Chris von Rueden. Tsimane man mediating a dispute over land)

The pre-agricultural past may have been more politically diverse than often assumed (see here), but it is likely that political egalitarianism predominated. As observed in many modern hunter-gatherers, political egalitarianism is a collectively-enforced emphasis on individual autonomy and freedom from coercion. A long-debated question, therefore, is why individuals in relatively egalitarian societies would acquiesce to greater political inequality, particularly where this wasn’t forced on them by outsiders.

In their recent tome The Dawn of Everything, the anthropologists Graeber and Wengrow argue that political transitions throughout history were the result of ideological experimentation, largely untethered to the material or demographic conditions of societies. Their argument gains apparent support from the fact that even some hunter-gatherers had chiefs and kept slaves. Hunter-gatherers from the Pacific Northwest coast of North America are the canonical example. Clearly, agriculture is not a necessary explanation of the “origins” of such inequality. Nor is it sufficient. Many societies that practice minimally intensive agriculture (i.e. horticulture) are relatively egalitarian.

Models that focus less on subsistence type per se have greater power to explain why societies differ in political inequality. Different models emphasize different determinants of inequality, which include: (1) reduced dependence on widespread food-sharing to buffer risk, which can weaken motivations to enforce political equality (see here); (2) larger and denser populations, which can increase the appeal of formal leadership as a solution to interpersonal conflicts, coordination problems, and collective action problems (see here); and (3) disparity in control of productive land and other forms of wealth, which engenders relationships based on patronage and indebtedness (see here).

Debate over these and other models continues because studies that compare models are few. Furthermore, tests tend to rely on archaeological cases studies or cross-cultural comparison based on ethnographic databases like the Ethnographic Atlas. These approaches typically lack fine-grained data on changes in inter-personal relationships to directly test parameters of the relevant models.

In my paper recently published in Evolution and Human Behavior, I present another approach: longitudinal observation of a current small-scale society (Tsimane horticulturalists), who retain some independence from state institutions and whose politics remain fairly egalitarian. Most extant small-scale societies like the Tsimane have been increasingly exposed to the threats and opportunities associated with market integration and inter-cultural exchange, which I argue can generate the conditions upon which various models of political inequality depend.

The Tsimane people live in villages ranging from 30 to 700 individuals in the tropics of lowland Bolivia. Their economy is based on food-sharing and collaboration in horticulture (plantains, manioc, rice, and corn), hunting, fishing, and gathering, which tend to be concentrated within extended families residing in the same or nearby households. Average individual income for the Tsimane is <2 US dollars per day, largely from the sale of horticultural products and lumber and from sporadic wage labor with loggers or cattle ranchers. Income opportunities accelerated in the 1970s, with the arrival of roads to the nearest market town.

Tsimane politics is largely informal. Conflicts tend to be resolved by the parties directly involved, and sometimes third parties within a village may step in to help mediate. Villagers also hold occasional meetings, which are used to mediate more intractable conflicts or to plan collective action, such as maintenance of community trails, confrontation of illegal loggers or other colonists, and negotiation with merchants and outside political bodies.

For my recent paper, I describe variation in men’s political inequality across four Tsimane villages, as well as variation over time within one of these villages. I measure inequality as the Gini coefficients of villagers’ rankings of each other, according to “whose voice carries the most weight during community debates”. The focus on men is largely due to an absence of data on women’s political influence beyond a single village. In that village, men’s political influence was more variable and on average higher relative to women’s political influence (see here).

I found that market proximity matters. Inequality in men’s informal political influence is greater the closer the village is to the market town, and increased over a twelve-year period in the village closest to the market town. So what about market proximity could explain these trends? Villages closer to the market have higher average household incomes, which could undermine the incentives to widely share food as well as the status-leveling that helps maintain such sharing. However, I found no evidence consistent with this possibility: average number of food-sharing partnerships did not decline with greater political inequality.

There is greater evidence that Tsimane political inequality reflects demand for leadership, in order to more effectively deal with increased intra- and intergroup conflict. In the more market-proximate and politically unequal villages, men report more interpersonal conflicts, particularly conflicts with non-Tsimane, and the most influential men perform a much larger share of conflict mediations, like the man in the photo at the top.

While income inequality did not clearly associate with political inequality either cross-sectionally or longitudinally, men who use their income to hire or indebt others may gain political advantage. Closer to the market town, a small percentage of field labor help is now paid rather than reciprocated in kind. However, the most influential men are only slightly more likely to be labor patrons, and only in the final year of analysis did labor patronage predict men’s influence independent of other predictors, including conflict mediation.

Wealth differentials will likely increase in the future as some Tsimane further scale up their cash cropping via labor patronage, while others opt for more traditional lifestyles. Over the longer term, land may become de jure privately owned at the household level in response to escalation of land conflicts. These changes may precipitate a shift from more mutually beneficial political inequality–motivated by a demand for leadership– to ever-growing and elite-enriching political inequality–enabled by differential resource control. Indeed, such a shift may have been characteristic of inequality increases throughout the Holocene (see here). Studies of the Tsimane and other small-scale societies in transition will help us better understand how continuous change in political inequality can precipitate more qualitative shifts, such as the emergence of chiefs or other inherited positions of coercive authority.

Read the original paper here: von Rueden, C.R. (2023). Unmaking egalitarianism: comparing sources of political change in Amazonian society. Evolution & Human Behavior, 44(6), 525-652.

Author’s Note: The paper describing the above was published as part of the Evolution and Human Behavior special issue, “Dispatches from the field: insights from studies in ecologically diverse communities: Part 2”. The special issue is dedicated to the late John Patton, and also acknowledges the recent passing of John Tooby. Their influence on my paper and the others in the collection is enormous. I am equally indebted to my dissertation advisor and frequent collaborator Mike Gurven, Hillard Kaplan, and the Tsimane Health and Life History Project. We recently established a scholarship fund for the first Tsimane women and men to attend university, in disciplines like medicine, law, engineering, and business administration. Consider supporting us in building a generation of Tsimane leaders with the capacity to meet their many challenges to a sustainable future.