Evolving our Understanding of Morphometric Cues to Behavior Through the Study of Nonhuman Primates

by Vanessa Wilson and Drew Altschul


Over the last 16 years, the study of human facial morphometry, and its potential links to social behaviour, has received a lot of attention. One metric in particular, the facial Width-to-Height ratio, has been linked to an array of dominance-like traits in males, such as aggression, achievement drive, psychopathy and (low) cooperation. In other words, men with higher ratios (i.e. relatively wider faces) tend to exhibit higher levels of dominance-like traits. Moreover, studies have found that people also tend to associate wider faces with being more dominant. The idea that we can ‘read’ certain traits in a person’s face is certainly an attractive one. But in reality, is such a relationship really so straight forward?

A number of studies have now cast doubt on the idea that these relationships are anything more than spurious. Indeed, early proposals that testosterone is the underlying mechanism that drives the relationship between aggressive, dominant male behaviours and wider faces are not strongly supported in the literature. There are several alternative explanations for what seems to be a tentative link between facial morphology and social behaviour. Amongst them is the evolutionary mismatch hypothesis, which proposes that facial cues to behavioural tendencies might have been salient in ancestral environments, yet no longer predict those tendencies in modern environments. Nevertheless, ancestral biases remain, resulting in a mismatch between existing behavioural traits, and how people predict those traits from facial features.

Where then, do nonhuman primates come into this? The problem with human-focuses studies is that, aside to the fact that most studies draw their samples from WEIRD populations (western, educated, industrialised, rich and democratic), by concentrating research on only humans, we learn little about the origins of facial morphology as a cue to social behaviour. If we really want to get into the evolution of the facial Width-to-Height ratio, or any other metric, as a behavioural cue, then we need to consider whether parallel relationships exist in other species. One theory that addresses the mechanisms underlying the link between face width and aggression, proposes that a wider zygomatic arch (producing a wider face) could improve skull strength, and therefore offers advantage in physical combat. Since humans live in relatively egalitarian societies, with low levels of in-group aggression, this could explain the weak findings for facial metrics as cues to traits pertaining to combat advantage. By examining whether similar relationships exist in species with lower levels of social tolerance and higher physical aggression, one can test this hypothesis.


“By concentrating research on only humans, we learn little about the origins of facial morphology as a cue to social behaviour.”


In our recent study, we examined links between facial morphometry and personality ratings in chimpanzees, a species that live in male-dominated, fission-fusion societies, where male displays of strength and physical aggression play an important role in social interactions. Notably, examination of chimpanzee personality dimensions on a 54-item scale reveals six components, five of which resemble the human ‘Big five’ (Openness, Conscientiousness, Extraversion, Agreeableness, Neuroticism), and a sixth that is labelled Dominance. Several of these components have been linked to observations of aggression in chimpanzees, in particular Dominance. We examined keeper-ratings on these six dimensions in relation to photo-derived measures of the facial Width-to-Height ratio, in a sample of 131 captive chimpanzees from zoos and research facilities in Japan, the UK and the USA. We found no evidence of sexual dimorphism in the facial Width-to-Height ratio, consistent with findings in humans. We did find a relationship between facial Width-to-Height ratio and the dimension Dominance, but in females, rather than males (as has been reported in the human literature), which was specific only to the western subspecies (Pan troglodytes verus).

At first glance these results may seem surprising. The differences in findings for males and females could, however, be explained by differences in rank stability with age. That is, females tend to maintain somewhat stable ranks across the lifespan, whereas males compete over social status, which tends to vary across the lifespan. Indeed, since male chimpanzees tend to be more aggressive than females, these findings do not support the hypothesis that the facial Width-to-Height ratio provides a combat advantage. The picture is perhaps more complicated than that, since our findings suggest that how social status is both achieved, and maintained, could play a role in whether the facial Width-to-Height ratio predicts dominant tendencies.

Moreover, we compared our findings with those from previous studies on humans, and bonobos, by examining differences in the strength of relationship between facial Width-to-Height ratio and social traits. We found that, compared to results for chimpanzee females and bonobos, the effect sizes for both humans and chimpanzee males were negligible, with the strongest effect emerging for bonobo Affiliative Dominance. Given that both bonobos and humans are considered to be more socially tolerant than chimpanzees, these differences suggest that social style (i.e. the level of tolerance a species exhibits) is not a strong predictor of trait-related variance in the facial Width-to-Height ratio, at least amongst apes.

So where do these findings stand with regard to current interpretations of the human literature? Alongside the accumulating results from brown capuchins, the Macaca genus, and bonobos, these findings suggest that the facial Width-to-Height ratio existed in a common primate ancestor, before the divergence of New World monkeys. Whilst questions remain about both the existence and strength of the facial Width-to-Height ratio as a cue to behavioural tendencies in humans, answers to these questions may be found by taking a comparative approach to understanding what selection pressures have driven this relationship. Specifically, examining broader differences in social style and rank stability could hold the key to understanding the variable nature of this relationship amongst primates.


“Our own recent evolutionary history, with the development of culture and language, could have provided alternative means to communicate dominance, reducing the need for facial cues to such traits”


For now, our own interpretations support the proposal of Wang and colleagues for an evolutionary mismatch in humans: our own recent evolutionary history, with the development of culture and language, could have provided alternative means to communicate dominance, reducing the need for facial cues to such traits. Yet the floor remains open for more thorough investigation, and we strongly encourage other researchers pondering this field to embrace comparative research as well as non-WEIRD samples, in order to understand the existence, origins and mechanisms of the relationship between facial morphology and dominance behaviour.



Read the paper: Facial width-to-height ratio in chimpanzees: Links to age, sex and personality

A Critique of Life History Approaches to Trait Covariation

by Brendan Zietsch


Life history theory has been promoted as a unifying framework for understanding trait covariation in the social sciences. Underlying this approach is the assumption that patterns of trait covariation across species, and the Darwinian principles thought to underlie those patterns, can be extrapolated to trait covariation across individuals within human populations. In particular, it is assumed that a ‘fast-slow’ continuum of life history ‘strategies’, observed across species, should be observed across individuals within human populations – not only with regard to traditional life history traits but practically all individual differences, including personality and psychopathology.

In my paper with Morgan Sidari we argue that these assumptions are not justified. The processes that create trait covariation across species and across individuals are fundamentally different, and so the two types of covariation need not be parallel or even related. This fundamental problem undermines a great deal of research in this burgeoning field, and warrants a rethink moving forward.

To illustrate the point, we use the simple example of body height. Humans are taller than rabbits because of their different genes. Individual humans also differ in height largely because of their different genes. But the processes that create genetic height differences between rabbits and humans (i.e. Darwinian evolution) are nothing like the processes that create genetic height differences between individual humans. The fact I am taller than a rabbit is primarily due to our different histories of Darwinian evolution over countless generations of different selective pressures; the fact I am taller than my friend or my brother has little (or nothing, in the case of my brother) to do with our different histories of Darwinian evolution, but rather my chance inheritance of more “tall alleles” compared to them. As with all individuals of European ancestry, many of my friends and I share nearly the same set of ancestors who were alive 1,000 years ago (and likely many ancestors more recent than that) – a very short period in evolutionary time. Therefore, the reason my friends and I are of different heights is largely independent of our different histories of Darwinian evolution. We are different heights mostly for the same reason my brother and I (who share all our ancestors) are of different heights – that is, the random shuffling process of Mendelian segregation during meiosis gave us different combinations of our ancestors’ genetic material. Overall, this example highlights why we cannot straightforwardly transfer the same evolutionary principles from the explanation of human-rabbit differences to human-human differences.


“Darwinian phenotype-environment matching at the species level and plasticity at the individual level are completely different processes and may or may not lead to equivalent predictions regarding trait covariation.”


The same argument applies to trait covariation. If environments that tend to favour large bodies also tend to favour high parental investment, then genes controlling the two traits will come to covary across species. There is no equivalent evolutionary process creating trait covariation across individuals. Selection and evolution can lead to phenotypic plasticity and adaptive calibration of individuals’ traits to their personal environments; but Darwinian phenotype-environment matching at the species level and plasticity at the individual level are completely different processes and may or may not lead to equivalent predictions regarding trait covariation. Similarly, there are different consequences at the species and individual levels in situations where selection on one trait depends on the level of another trait. If genes for high parental investment are advantageous in a large species and disadvantageous in a small species, genes for large body size and genes for high parental investment will tend to go together across species, and likewise genes for small body size and low parental investment. But there is no equivalent evolutionary process by which variation in different traits within a population can be combined based on how well they work together. Darwinian evolution cannot combine “tall alleles” with “high parental investment alleles”, and “short alleles” with “low parental investment alleles”, within a sexually reproducing population in the same way as it can across species, because of Mendel’s Law of Independent Assortment: segregating alleles are transmitted to offspring independently of each other, so allele configurations are not inherited.

We explain why exceptions to Mendel’s Law of Independent Assortment – correlational selection, physical linkage, non-random mating, and pleiotropy – don’t change our central point. We also discuss adapted developmental plasticity, where variation and covariation of life history-related traits is shaped by environmental conditions during an individual’s development. In particular, we note behavioural genetics research that shows little influence of early environment on trait variation and covariation, and why these findings pose problems for these plasticity-based life history accounts. Further, we discuss why proposed trade-offs between specific life history traits – trade-offs that are typically on the within-individual level – need not translate to covariation of those traits across individuals.


“Much of the life history work on trait covariation in humans does not have a solid theoretical grounding; there is little basis for the fast-slow continuum as a framework for understanding human trait covariation.”


Overall, we conclude that much of the life history work on trait covariation in humans does not have a solid theoretical grounding. In particular, there is little basis for the fast-slow continuum as a framework for understanding human trait covariation. Given the frequent attacks on evolutionary psychology from other disciplines, our field must be especially vigilant for conceptual flaws in the underpinnings of our research – otherwise, we risk validating those criticisms. Those using life history theory to study individual differences and trait correlations must ensure their paradigm is properly connected to the fundamentals of evolutionary theory.



Read the paper: A critique of life history approaches to human trait covariation

2020 HBES Award Information

Dear HBES members,

There have been many questions about how our annual society and conference awards will be handled given the cancelation of the annual HBES conference that was scheduled to be held in June. The Executive Council has made the following decisions with regard to the society and conference awards.

2020 HBES Early Career Award and Lifetime Achievement Award

Nominations for the 2020 HBES Early Career Award and Lifetime Achievement Award will still be considered this year, and will be formally celebrated at HBES 2021 in Palm Springs (along with the HBES awards for 2021). We have, however, extended the deadline for the nominations to July 1, 2020 given the pandemic situation. Please see our website (see the ‘Nomination’ tab under each award) for eligibility, application guidelines, and submission link.

2020 New Investigator Award and Postdoctoral Award

The New Investigator Award and Postdoctoral Award will not be conferred this year because they require a talk at the annual HBES conference, which has been cancelled. Because for some award candidates 2020 was the last eligible year for one of the awards, we will be extending the eligibility by one year for the 2021 HBES conference awards. Specific eligibility requirements will be available at a later date when the HBES 2021 conference website is live later this year.

Thank you for your understanding during this difficult situation.

The HBES Executive Council

Why Do We Stereotype Others by Sex and Age?

by Oliver Sng, Keelah Williams, & Steven Neuberg


The study of sex and age stereotypes—the general beliefs we hold about others based on their sex and age—has had a long history. In a recent paper, we present a new perspective to thinking about this topic. Specifically, we propose that social perceivers are actually “lay adaptationists”. In other words, although lay perceivers are not aware of formal evolutionary theories (e.g., parental investment, life history), they nonetheless pick up on and generate predictions about how others’ sex and age influence their goals and behaviors.

From this perspective, perceivers categorize and stereotype others by sex and age, because another person’s sex and age are associated with their goals (e.g., learning, mating, parenting), which in turn are associated with distinct opportunities and threats they might pose (e.g., potential mates, potential mate competition). This generates several insights.

First, it is not sufficient for perceivers to be categorizing others in terms of just sex, or just age. This is because goals vary by the interactive combinations of sex and age (e.g., men are more oriented towards short-term mating goals than women are, but especially so at younger ages). To usefully represent distinct social opportunities and threats, perceivers should categorize others in terms of the combination of others’ sex and age.

Indeed, they do so. Using a memory recall paradigm often referred to as “who-said-what”, we find that perceivers are more likely to confuse individuals of the same sex or of the same age group (e.g., confusing women with other women instead of men, confusing 60 year-olds with other 60 year-olds instead of 20 year-olds). More important, they are especially likely to confuse individuals of the same sex and age (e.g., confusing 20-year-old women with other 20-year-old women instead of 60-year-old women or 20- and 60-year-old men). Hence, perceivers mentally group others not by sex or age independently, but by the interaction of both.

The same principle should apply to stereotypes—beliefs about how women and men of different ages are like. Indeed, in another set of studies, we find that too. For example, perceivers believe that men are more oriented towards seeking short-term partners than women are, but this sex stereotype is stronger for stereotypes of younger (e.g., 28-year-olds) than older individuals (60-year-olds). The reverse is observed for stereotypes of long-term mating orientation. Young women (e.g., 28-year-olds) are stereotyped to be more oriented towards seeking and maintaining long-term relationships than young men, but this stereotype disappears for stereotypes of older individuals (e.g., 60-year-olds). Hence, perceivers also hold interactive sex and age stereotypes.

Finally, the current perspective also has implications for thinking about certain widely studied sex stereotypes. A considerable literature has accumulated on sex stereotypes of agency and communion. Agency comprises traits that focus on self-assertion, such as being independent and competitive. Communion comprises traits that maintain harmonious social relationships, such as being caring and understanding.

Why are men typically stereotyped as more agentic than women? One explanation may be because men are stereotyped as more oriented than women towards short-term mating goals (as just mentioned above), and the pursuit of short-term mating goals likely requires more agentic behavior, such as competitiveness and dominance. If the sex stereotype of agency is indeed derived from sex stereotypes of short-term mating goals, then presenting perceivers with direct information that both men and women are similarly oriented towards seeking short-term mates should eliminate the sex stereotype of agency.

“Providing perceivers with direct information about the adaptive goals (e.g., mating, parenting) that male and female targets are engaging in seems to override prominent sex stereotypes of agency and communion.”

Indeed, that is the case. Perceivers presented with a male or female target, without any additional information, stereotype the man as more agentic than the woman. However, when perceivers are given information that a woman and a man are similarly spending time looking for short-term partners, the woman and man are stereotyped as equally and highly agentic.

A similar logic could be applied to thinking about sex stereotypes of communion. Why are women stereotyped to be more communal than men? One explanation is that the sex stereotype of communion may be derived from sex stereotypes of long-term mating goals (of women as being more oriented towards such goals than men), because seeking and maintaining long-term mating relationships requires communal traits such as kindness and care. If this is so, then perceivers presented with men and women who are similarly engaging in long-term mating goals should be viewed as similarly communal.

This prediction is borne out, too. In the absence of additional information, perceivers stereotype a female target as more communal than a male target, consistent with the stereotype. However, when told that both targets have and spend time with a long-term relationship partner, the male and female targets are viewed as equally communal

In general, providing perceivers with direct information about the adaptive goals (e.g., mating, parenting) that male and female targets are engaging in seems to override prominent sex stereotypes of agency and communion. Prominent sex stereotypes appear to emerge from people’s stereotypes about sex and age differences in the relative prominence of adaptive goals.

To summarize, perceivers categorize and stereotype by the interactional combination of others’ sex and age, and these stereotypes suggest that perceivers are lay adaptationists in certain ways. For instance, just as parental investment theory predicts that males in our species are more likely to invest in mating effort than women are, lay perceivers also “predict”, through sex and age stereotypes, that men (and particularly young men) are more oriented than women towards short-term mating goals and behaviors. These adaptive goal stereotypes may in turn underpin other stereotypes, such as sex stereotypes of agency and communion.

The findings outlined above may seem intuitive, and intuitive findings are sometimes devalued. But that the findings seem intuitive to you as a reader is itself something the perspective would predict, simply because you are also a lay adaptationist (and likely also a professional adaptationist!). In other words, you are likely also using the sex and age of others, interactively, to predict their goals and behavior. Hearing that people categorize and stereotype by sex and age in these particular ways should therefore be unsurprising.

The idea that perceivers may be lay adaptationists is useful beyond enhancing our understanding of the social perception of sex and age. In other work, we apply a similar approach for better understanding race stereotyping. Specifically, certain stereotypes of Black and White Americans may not be about race, per se, but instead may reflect what we call ecology stereotypes—beliefs about the traits of individuals who live in more versus less harsh and unpredictable ecologies. Supporting this, we have found that providing perceivers with direct information about a Black or White individual’s home ecology can override race stereotypes of traits such as impulsivity and aggressiveness.

Thinking about perceivers as lay adaptationists lends a new way of thinking about social perception and stereotyping. Stereotyping, in particular, is traditionally presented as an outcome of “lazy” minds trying to simplify the world. The current work presents a more nuanced picture. Social perceivers are sensitive to the interactions of sex and age in thinking about and predicting the traits of others. When making social inferences about agency and communion, perceivers also prioritize information about an individual’s relevant goals, over the general category an individual belongs to. Indeed, our stereotypes may be more strategic than typically thought.




Read the paper: Sex-age stereotyping: Social perceivers as lay adaptationists

Comparing Evolutionary Models of Sexual Initiation

by Kristin Snopkowski & John Ziker


Life history theory examines how organisms allocate energy throughout the lifespan.  While it was originally developed in biology, more recently a large number of researchers have begun to use life history theory as a way to examine phenotypically plastic responses to early life factors in humans.  This research has examined how family dynamics and stressors earlier in life influence ‘life history events,’ such as pubertal timing, age at first reproduction, age at sexual initiation, and more rarely, investment in offspring.

In this research, we tested a variety of different evolutionary hypotheses that have been proposed – frequently under the theoretical umbrella of life history theory – to see which were best at predicting sexual initiation among a sample of Canadian adolescents who were followed longitudinally since birth (over eight waves of data collection).  The National Longitudinal Survey of Children and Youth, a survey conducted by Statistics Canada, provides a wealth of information about children and their families.  This allowed us to examine a variety of different factors that have been predicted to influence the timing of life history events (although, our analysis only examined sexual initiation).  This includes factors such as: childhood psychosocial stressors, such as parenting behaviors, socioeconomic status, stressful events; paternal investment indicators, including contact with father, parental divorce, emotional closeness with father; mortality cues, for example, health of caregivers, adolescent chronic illness; unpredictability, such as changes in childcare and household moves; social support, for instance, adolescent social support other than peers; prenatal factors, including birth health and gestational diabetes; and intergenerational conflict indicators, measured as having half siblings.

We utilized a model selection procedure where we minimized AIC scores to predict whether adolescents had engaged in consensual sexual intercourse by the ­eighth wave of data collection (age 14/15). After identifying the predictors that minimized the AIC score for each variable set, we ran all combinations of models (since we had eight sets of variables, this led to 256 different combinations).  We then examined all models within three of the best AIC score (indicative of having a similar level of statistical support) and calculated the importance score for each variable set.

“The lack of an association between paternal investment variables (frequently discussed as ‘father absence’) was surprising given the frequency with which it has been found in other contexts”

The results showed that psychosocial stressors (either early-life or adolescent), mortality cues, and intergenerational conflict variables were included in all of the top models. Prenatal factors were included in the top five models. Social support and unpredictability were common across top models (but not included in all models).  There was greater support for early-life psychosocial stressors over stressors during adolescence.  Paternal investment variables were not included in any of the top models.  Importance scores mirrored the AIC results: extrinsic mortality cues had the most importance, followed by intergenerational conflict, early childhood psychosocial stressors and prenatal factors. Social support and unpredictability predictors followed, with importance scores between 0.58 and 0.54.  Finally, paternal investment has the lowest importance (0.11).

As previous research has found, there was good support for early-life psychosocial stressors and extrinsic mortality cues being associated with sexual initiation by age 14/15. As predicted social support, unpredictability, and prenatal factors were also associated with sexual initiation.  Novel results of this study include the role of half-siblings and its association with sexual initiation, as predicted by intergenerational conflict models (a few recent papers have also found evidence of this).  The lack of an association between paternal investment variables (frequently discussed as ‘father absence’) was surprising given the frequency with which it has been found in other contexts (mostly western contexts, like the one we examined in this study).  It is possible that intergenerational conflict factors confound the effect of parental divorce, so it is important to include both factors in future models to detangle their effects.



Read the paper: “Sexual initiation among Canadian youth: A model comparison approach of evolutionary hypotheses shows greatest support for extrinsic mortality cues, intergenerational conflict, and early life psychosocial stressors


Getting Refunds for Flights and Lodging for Cancelled HBES 2020

Syndicated columnist, author, and longtime HBES member Amy Alkon here.

Around March 26, I saw tweets from grad students that American Airlines and AirBnb were refusing refunds for flights and lodging for June HBES, cancelled due to coronavirus. Other airlines may also be refusing to refund.

Delta, thankfully, is refunding money.

A number of us tried to use social media to get American Airlines and Airbnb to give refunds, but they didn’t budge.

There may be another way. I’ve just reached out to a newspaper colleague, syndicated travel columnist and author Christopher Elliott, whom I’ve known for 20 years and respect. On his nonprofit travel consumer advocacy website — Elliott.org — he takes on cases like this, and gets resolution, mediating between travelers and airlines. He has the power of the respect and readership he’s earned and big businesses often back down and reverse no refund policies.

Elliott tweeted back to me that he is open to considering taking this on as a case. Knowing him, I suspect he will take this on.

I have not personally lost money, but I suggest that some of you who have had refunds denied band together and collectively write to Chris via his help link at his website: elliot.org/help (This is the way he asks that requests for help be submitted.) I think that collectively writing him (at least two or three people banding together) makes this a more persuasive request (see end for contact information).

An important crux of your appeal, in my opinion: What many people don’t realize is that grad students and ECRs are often living on financial fumes, and the hundreds of dollars or more that are being kept by these companies are huge sums of money — especially at a time when gig work many were doing to make ends meet has dried up.

-Amy Alkon


If you are a student who is struggling to get refunded for flights and lodging related to HBES 2020, please contact HBES Student Representative Cari Pick (studentrep@hbes.com). Cari will be organizing a collective effort for those interested.


Note: This effort is NOT for conference registration refunds, which are handled by the conference organizers. If you have questions about your registration refund, please contact the conference organizers at hbes2020@gmail.com

A Letter from the Editor of Evolution and Human Behavior

Dear HBES members,

I hope this letter finds you all in good health and relatively sane. I am pleased to give the membership an update on EHB. As many of you already know, Elsevier recently migrated the online submission system to Editorial Manager. Together with the production staff and the Editorial Board, I have been working to identify issues and improve usability. I expect it will take a few more cycles to work out all the kinks so I ask for your continued patience.

The Editorial Board continues to work through this challenging time to compile several upcoming issues and I’d like to share them with you. Slated for 2020 are two special issues. The first special issue, organized by Coren Apicella, Ara Norenzayan, and Joe Henrich is on non-WEIRD research and due out in September. The second special issue, organized by Willem Frankenhuis and Dan Nettle, is on Life History Theory and due out in November. This will close out volume 41. For each of the special issues, please be on alert for calls for commentaries. A few selected commentaries will be compiled and appear in a subsequent issue early in 2021. More information will be provided in the introductory article/editorial that will accompany each special issue. There are 2 more special issues in the works and I will provide an update as these take shape.

In issue 6 of 2019, EHB piloted a new format—featured article, commentaries, and author response. The test article for this format was on current debates surrounding menstrual cycle effects and, from the feedback I’ve received, several HBESers felt it was a valuable contribution to the literature. I strongly believe it is important to advance the field’s knowledge across all content domains and one way to do this is to organize effective discussions. There are several topics across anthropology, biology, economics, philosophy, and psychology in need of clarification and (friendly) debate. My intention is that this new format will provoke discussion, generate collaborations, and solidify our scientific foundations. There are 6 issues of EHB per year and I would like to move toward including a featured article with commentaries and response in each. Currently, selection of target articles and commentaries is initiated by the Editor, but I welcome inquiries. Note: Not all articles will lend themselves to this format.

Typically, at the annual HBES meeting, we announce the winner of the Margo Wilson Award, an award made by the Editorial Board for the best paper published in EHB in the preceding year. Selection for the 2020 Margo Wilson Award for the best paper published in EHB in 2019 will be announced in the summer newsletter.

Finally, there are several changes to the Editorial line-up I’d like to share. First, a warm welcome to four new Associate Editors: David Puts, Greg Bryant, Tess Robertson, and Andy Delton. They join Coren Apicella, Rebecca Sear, Josh Tybur, and Willem Frankenhuis to round out the 2020 Editorial Board. Second, Dan Hruschka, after 7 years of service, will be stepping down as Associate Editor. Dan’s contributions to the field have been immeasurable and I am grateful to have had the chance to work closely with him on the journal. Thank you, Dan, for everything you’ve done.

I look forward to receiving your excellent scholarly works via the online submission portal. As always, my mission as EiC of HBES’s journal is to raise the level of discourse, advance knowledge within and across borders, and disseminate to the academy, media, and public our multi-disciplinary research on evolution and human behavior.


Stay well,

Deb Lieberman

Editor in Chief, Evolution & Human Behavior

Important COVID-19 Information Regarding HBES Activities

The COVID-19 pandemic is an ongoing situation that is causing much uncertainty for universities and scientific societies. The HBES Executive Council is continuously monitoring the situation and will communicate with the membership as new updates become available. Below, we have important information regarding upcoming HBES activities. We appreciate your understanding and cooperation during this difficult time.


HBES 2020

Dear HBES Community:

Following discussion with the HBES Executive Council, HBES 2020 in Detroit is cancelled. This is due to the current global spread of COVID-19 and uncertainty regarding public health and travel in the foreseeable months. All HBES 2020 conference registration fees will be refunded via PayPal. Abstract submissions have not been reviewed and will not be carried forward to the 2021 conference.

This decision was difficult to make but we and the HBES Executive Council felt it is the responsible course of action. We apologize for any inconvenience and are deeply disappointed that there will be no HBES conference this year. HBES 2021 will be in Palm Springs, California.

Please contact us at hbes2020@gmail.com with any questions.


Todd Shackelford and Viviana Weekes-Shackelford



HBES Funding Grants

Dear HBES Community:


Due to the current global COVID-19 pandemic, HBES will not be entertaining or funding proposals for the spring deadlines which include the General Funding Grant (due May 1) or the Student Funding Grant (due March 31). We apologize for any inconvenience this causes for event planning. We will reevaluate the fall deadline for the General Funding Grant (due Nov 1) and communicate with the membership when new updates are available.


Please contact HBES President Leda Cosmides with any questions, president@hbes.com.



HBES Executive Council

Peer Teaching in Hunter-Gatherer Societies

Peer Teaching in Hunter-Gatherer Societies

By: Sheina Lew-Levy


One of our species most adaptive traits is our ability to transmit, and improve upon, knowledge from one generation to the next. This reliance on cumulative cultural knowledge has allowed humans to move into diverse, and sometimes challenging environments. For example, we are the only species that can simultaneously thrive in the Kalahari Desert and the Arctic Circle. To do so, we have developed cultural adaptations, such as specialized hunting techniques and clothing.

How children and adolescents learn these cultural technologies is of growing interest to psychologists and anthropologists alike. Teaching, defined here as a behavior performed by one individual in order to facilitate learning in another individual, is one way in which knowledge is transmitted between individuals across and within generations. While we are all familiar with classroom-style teaching, teaching can be much subtler, such as demonstrating, offering feedback, teasing, and assigning tasks.

Cross-cultural studies suggest that parents play a central role in teaching infants (1), but less is known with regards to whom older children receive teaching from. Conversely, while anthropological and psychological studies suggest that older children in diverse settings learn from peers (2), much less is known with regards to peer teaching specifically. In hunter-gatherer societies, where much of children’s time is spent in a multi-aged, mixed-sex playgroup, learning about subsistence is likely to occur through teaching during play and participation in work with other children.

Learning from other children may be particularly adaptive: in the peer group, children can acquire basic competencies. Later on, they can seek teachers from whom they can learn more complex and specialized tasks (3). Also, since teaching can be time consuming, it’s likely that teachers will be individuals who have the most to benefit from the other’s success, such as parents. However, siblings are as related to each other as they are to their parents. Thus, siblings have a lot to gain, from an inclusive fitness standpoint, in teaching their brothers and sisters.

In order to examine whether peer teaching was common in hunter-gatherer societies, we conducted research among Hadza and BaYaka foragers. The Hadza live in the arid-savannah woodlands of Tanzania, and subsist on honey, baobab, berries, tubers, and meat hunted with bows and arrows. Increasingly, the Hadza also rely on maize and other grains provided to them by missionaries, ethno-tour companies, or that are purchased from neighboring pastoralists. The BaYaka live in the dense tropical forest of the Congo Basin. They subsist on hunting with spears, guns, and traps, fishing, gathering tubers, fruit, insects, wild vegetables, honey, and on small horticultural gardens of cassava and maize.

While this suggests that child-to-child teaching is the norm in the hunter-gatherer societies surveyed, we also found considerable cross-cultural variation in the identity of child teachers.

With the help of an interpreter, I followed 35 Hadza and 38 BaYaka children and adolescents ranging in age from 3-18 years for four hours each. During this time, I recorded their activities every minute, as well as any teaching interactions. We then examined patterns for teaching using the Social Relations Model, a type of social network analysis (4). We focused particularly on the teaching of subsistence skills and knowledge. We wanted to understand whether peer teaching occurred in childhood, and adult-child teaching in adolescence, and whether teaching between siblings was common. We also wanted to understand cross-cultural variation in these behaviors.

We found that only 25% of the observed teaching occurred in adult-child dyads, even though children were in proximity of adults 57-69% of the time. While this suggests that child-to-child teaching is the norm in the hunter-gatherer societies surveyed, we also found considerable cross-cultural variation in the identity of child teachers.

First, we found evidence for the multi-stage learning model, where children learn from peers in the playgroup, and from adults in adolescence among the BaYaka. However, we did not find this trend among the Hadza. This finding may be due to the particular socialization practices of each society. Hadza parents and other community members facilitate children’s foraging by making them small, but fully functional, bows, arrows, and digging sticks (5). Children are encouraged to use these tools while foraging, which scale up as children grow. Using these tools, Hadza children are competent foragers by middle childhood, producing up to 50% of their daily caloric needs, depending on the season (6). By providing children with functional tools, adults may limit the need for direct adult teaching, since children can learn through participation. Among the BaYaka, receiving fully-functioning child-sized tools does occur, but is rarer. Further, while children make their own tools, such as slingshots and rat hunting spears, these tools are used by children only (7), and children’s foraging returns from these activities are low (8). As a result, BaYaka children may have less opportunities to practice adult subsistence with child-sized versions of adult tools, and thus, may require more adult tutelage later on in life.

Second, while teaching occurred more frequently between related dyads than unrelated dyads in both societies, sibling teaching was more common among the Hadza than the BaYaka. These differing results may be due to the structure of camps. Among the Hadza, camps tend to be spread out, while among the BaYaka, camps are much smaller. As a result, BaYaka children are in close proximity to, and in closer range for receiving teaching from, all adults living in camp throughout the day. In their larger camps, Hadza children are more likely to be with their nuclear family while at home, resulting in more opportunities to be taught by these closely related individuals, including siblings. As a result of these different settlement structures, the nuclear family may play a greater role in knowledge transmission among the Hadza than the BaYaka.

Taken together, the results of our study suggest that children and adolescents are active teachers from an early age. By facilitating each other’s knowledge acquisition, children may also contribute to a more rapid, and potentially less costly, transfer of knowledge. Furthermore, our study shows that aspects of socialization and settlement structure may mediate which children teach, and when, calling attention to the need to take account of contextual aspects when investigating how children learn across diverse societies.


Read the research article here.


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Children’s Understanding of Dominance and Prestige in China and the UK

Children’s Understanding of Dominance and Prestige in China and the UK

By: Anni Kajanus*, Narges Afshordi*, & Felix Warneken

*joint first authors


Children recognize social rank differences between individuals from early on, for instance associating bigger physical size with dominance. However, dominance—gaining high rank through force or threat of force—is only one mechanism of social rank in human societies. Prestige – merit and respect in the eyes of others – is another important strategy to gain rank. While dominant individuals bully their way to the top, others follow prestigious individuals willingly. In this paper, we set out to test whether children might be able to distinguish dominance and prestige from each other based on a number of cues. We were also interested in how children’s understanding of dominance and prestige develops in different cultural contexts. More specifically, we compared children’s expectations about who would win a desired resource in a conflict between a low-ranking individual and a high-ranking one. This second question was inspired by Kajanus’ ethnographic studies in Nanjing, China, and London, UK. In Chinese culture, yielding to elders and those in positions of authority is valued. As a result, yielding to others can be a signal of lower social rank, as it is in many Western cultural contexts. In addition to this, however, people sometimes also yield to those in lower positions, for example to demonstrate their ability to control emotional impulses, or to skillfully stop conflict situations from escalating. In these situations, yielding is a sign of higher, rather than lower, social rank. Chinese children learn this value from early on, although the complexities of applying it successfully in social situations may take many years to master (Kajanus, forthcoming). In sum, yielding can be a sign of either lower or higher status in China, but generally only of lower status in the UK.

When given the choice between the dominant and prestigious individuals, older children inferred that the subordinate would approach the prestigious character and like them, but fear the dominant character.

With this in mind, we tested children in the UK and China (5-7 years, and 9-12 years, n=40 for each age in each country). Experiment 1 examined the age at which children distinguish dominance and prestige. Children watched simple animations involving three characters that established the central character as subordinate to both a dominant and a prestigious character. In the animations, we used different cues to demonstrate some typical features of dominant and prestigious individuals. For instance, the dominant character imposed her will on the subordinate without ever being asked to intervene, while the prestigious character shared an opinion in a friendly way only after being consulted. We found that both age groups of children in both countries easily recognized the social rank differences between the high-ranking (i.e. dominant or prestigious) characters and the low-ranking one. Further, when given the choice between the dominant and prestigious individuals, older children inferred that the subordinate would approach the prestigious character and like them, but fear the dominant character. Younger children also made similar inferences, but were less successful than their older counterparts. In addition to finding that children differentiate dominance and prestige, this experiment provided empirical confirmation that our animations depicted dominance and prestige in ways that were interpretable to children in both places. This gave us the opportunity to use the same animations in order to ask if children in China and the UK have similar or different expectations about who would win a conflict. Before testing children, however, we first wanted to know whether there were differences in adults’ expectations. We tested 40 adults from each country online. We established the roles of subordinate, dominant, and prestigious using the same cartoons as before. We then presented two cases of conflict over resources (subordinate vs. dominant, and subordinate vs. prestigious), and asked who would win. Even though adults in both countries predicted that the dominant and prestigious individuals would overcome the subordinate, Chinese adults were less likely than British adults to do so in the prestige case. That is, Chinese adults were less likely than British ones to think that the prestigious person would win the resource. Thus, we found some evidence of differences between the two populations in their views on conflicts between people of differing social rank.

Finally, we explored how cultural models of hierarchy and conflict influence children’s inferences about the outcome of conflicts between high- and low-ranking parties. Testing new samples of children (n=40 in each age in each country) in this task, we found that younger children in both countries failed to make systematic inferences about who would win. While six-year-old children were able to infer dominance and prestige from their associated cues, they apparently did not insert social rank into their reasoning about other inferences such as who would win a conflict. Older children in the two countries, however, responded differently from each other. Those in the UK, like adults, thought that high-status characters would win. In contrast, older children in China made no consistent prediction in favor of the high-status parties. Chinese children’s responses and importantly their justifications indicate that they are still grappling with the complex norms about who should yield and when. Overall, these experiments provide strong evidence for a culturally-influenced aspect of hierarchical relationship understanding across two populations, as well as pointing to potentially universal aspects of rank-reasoning.


Read the research article here.