The evolutionary origins of fair fights

by Aaron Sell

In early July 2004, the lead singer of Misfits – Glenn Anzalone (better known as Danzig) got into an argument with a fellow musician Danny Marianino backstage after a concert. After some aggressive words, Danzig pushed Danny back. It is important to know that Danzig was widely known for his aggressive and formidable nature, his deep baritone singing voice, and his muscular build. His body type was so befitting of a muscular hero that he was approached to audition for the role of Wolverine in the original X-men movie.  He was also a practitioner of Jeet Kune Do, the martial arts style of Bruce Lee, and a student of Muay Thai. And so, one can imagine his fans reaction when, following Danzig’s push, Danny promptly knocked the singer unconscious with a rapid right hook to the face. Not yet knowing he was unconscious, his fans yelled for him to kick Danny’s ass, but upon realizing he was no longer sentient, a Danzig fan yelled out, “Cheap shot.”  The video has been immortalized online.

Like most human concepts, the “cheap shot” or “unfair fight” or “sucker punch” are immediately intuitive, but contain a computational complexity to them that requires careful scientific study to map. What exactly is a cheap shot? How can a fight, which involves two people (usually men) beating each other until one is incapacitated or gives up, be in any way “fair”? “Fair” usually means evenly or equitably divided, but a fight is a fight precisely to determine a winner and a loser – one gets victory, the other shame and injury. “Fair” means something else here.

Let us start with first principles. Fights are dangerous, but contain useful information about who is a better fighter. This information was of crucial value to our ancestors; so much so that we appear to have evolved numerous complex perceptual mechanisms for assessing the fighting ability of men (Sell et al. 2009; Sell 2012). However, some aspects of fighting ability cannot be perceived by the visual system; for example, reaction time, hand-eye coordination, pain thresholds, etc. Only a bout of aggression reveals these in their sum and interactions, and so the outcomes of such fights serve as a particularly accurate signal of fighting ability.

However, fighting is inherently costly and dangerous. And so natural selection has designed, in many animals including humans, ritualized bouts of aggression wherein the organisms fight using restrained attacks meant to demonstrate fighting ability while diminishing the chance for lethal or injurious aggression. Cichlid fish, for example, will “tail beat” at each other generating waves that crash into their opponents and reveal their bodily strength. Only if those early less lethal means of aggression fail to reveal a victor do they escalate to actual biting. Similar patterns can be seen among housecats who will “punch” each other with claws withdrawn before using fangs. Danzig demonstrated the typical human pattern of pushing and shoving at the start of a typical fight.

The accuracy of these bouts, however, can be compromised by temporary circumstances that make a weaker fighter more likely to win, e.g. they attacked a sleeping opponent. In such a circumstance, the outcome of the fight is no longer a valid cue of fighting ability. Therefore, the outcome of such a fight can be dismissed (at least in part) as a cue of fighting ability. On this theory, a “fair” fight is one that is free of temporary asymmetries in a fighting ability.

In a study run on a sample of 300 US citizens, Daniel Sznycer, Matt Meyers, and I, showed that fights are deemed “unfair” when they contain such asymmetries. For example, in one case a teenager had injured his arm in gym class before a fight. In the control case, the teenager’s injury had recovered. Those subjects that read about the injured arm, found the subsequent fight unfair. In other cases, subjects read about a fight where the putative winner had help from a friend (unfair), was unprepared for aggression (i.e. “sucker punch”, unfair), or used a weapon when their opponent had declined to use it (unfair). In my favorite case, subjects read about an escalating fight with rocks and a tire iron. The two conditions contained exactly the same words, but in the “rapid escalationcondition the winner used the tire iron early in the fight, and in the “slow escalation” condition he used it later in the fight. When the winner used the tire iron early it was deemed unfair. When used late, after the opponent had a rock…it was fair. This is likely what Danzig’s fan was referring to when she called the punch a “cheap shot”; Danzig was in the pushing and shoving portion of the fight, while Danny rapidly escalated to a punch.

The evolutionary function of analyzing fairness in a fight was demonstrated when we asked subjects who would win a rematch if the fighters fought again (after they had recovered). In all but one of the five cases, there was a penalty assigned to a fighter who won unfairly. If they had won unfairly in their initial fight, subjects predicted they would be less likely to win a rematch. In short, “cheating” to win makes you seem weaker. And thus, Danzig’s fan was asking us to discount the fight and refrain from concluding that the Misfit’s singer was weaker than Danny.

Additional implicit fighting rules are contained in a concept of “honor”, and serve to minimize the costs to the combatants. For example, continuing to hit an opponent that has already surrendered was not deemed “unfair” but was considered immoral and dishonorable. Similarly, challenging and defeating someone who was clearly weaker (e.g. an elderly professor) was seen as dishonorable, even though the fight did show in a valid way who was a better fighter.

In short, humans appear to have evolved concepts (similar to those at work in other animals) that contain rules for combat meant to preserve the accuracy of assessing fighting ability while minimizing costs to the combatants. These rules include the absence of temporary asymmetries that bias the fight and tactical restraint that limits the kinds of attacks that are permissible unless it is part of mutual simultaneous escalation, e.g. eye-gouging, knees to the groin, weaponry, etc.

The computational analysis of fairness and honor in fights is just beginning, but the functional design of the concepts and their widespread existence in the animal kingdom demonstrate that only an evolutionary psychological perspective will be able to explain it.

classical statue of wrestling

Does facial shape predict real-world fighting ability in men?

by Neil Caton, Samuel Pearson, & Barnaby Dixon

The presence of dedicated pre-registered replication submissions in peer-reviewed journals is important for maintaining and improving the self-correcting tendency of the scientific enterprise. Replications inform us when we have (un)knowingly been led astray, and given the alarmingly high rates of false positives found in psychology to date, it is clear that we need more replications if the field is to continue separating the wheat from the chaff.

We recently conducted a pre-registered replication of a popular and influential study by Třebický et al. (2013) that was published in Psychological Science. This was the first study to provide scientific evidence for the claim that the same facial features are associated with both real-world fighting success and dominance judgments. Třebický and colleagues were the first to use Ultimate Fighting Championships data in the psychological sciences – a novel, creative, and unique idea. They correlated the entire facial morphology of UFC fighters’ with their fighting success and perceived aggressiveness. Men’s facial features predicted their actual fighting success, and participants could unconsciously perceive their fighting success simply by looking at their face. In our eyes, this is an important finding using a creative methodology that provides the first evidence in support of the claim that the face may be shaped by intrasexual selection—a long-standing debate in evolutionary face research.

Our acclaim for Třebický et al. (2013) led us to read the paper multiple times. Over those readings, several of study’s methodological details struck us as a cause for concern, and hence, formed the rationale for our decision to pursue a replication. Firstly, the association between facial shape and fighting success was found only in the combined sample of 19 light heavyweight and 14 heavyweight fighters. Second, Třebický and colleagues excluded certain groups of participants (e.g., men with moustaches and beards, Africans and Asians) prior to analysis, and the results were slightly under the significance threshold. There was no explanation for these exclusions in the original paper, likely owing to the tight word restrictions of Psychological Science at the time. Finally, Třebický and colleagues examined which facial structures were associated with actual fighting success and perceived aggressiveness, but not those associated with perceived fighting ability. While Třebický and colleagues examined the facial traits associated with fighting success, this doesn’t necessarily mean that participants perceived these traits as cues to fighting success (particularly when considering that Třebický and colleagues found that perceived ability did not significantly predict actual fighting ability). Overall, we acknowledge that Třebický et al. (2013) was the first study on the topic, and therefore there was no standardised process at the time for this creative and novel methodology.

To form the dataset for our replication project, we collected fight statistics, body composition and morphology, demographic information, and photos of 516 male fighters in the Ultimate Fighting Championship. We attached 36,636 facial landmarks to these 516 faces. We then collected data from 1,000 United States-based online raters to judge these 516 faces on perceived aggressiveness and fighting ability.

Consistent with the original study, we found that men with masculine facial features (e.g., large nose, deep-set eyes) were seen as more aggressive, independent of their body size. We also found novel evidence that men with masculine facial features were seen as better fighters, which was because these men were seen as being bigger overall. These analyses between facial shape and perceived fighting ability were not performed in the original study, but was our novel extension of the original study. We did not find an association between facial structure and fighting success. There could be several reasons for this non-significant association: the UFC contains the best fighters in the world, mixed-martial-arts competitions are often legally and ethically required to have weight categories, and/or win percentage may not be an ideal reflection of pure fighting success. If men with masculine facial features are seen as better fighters because they’re bigger overall, then men’s masculine facial features could predict their fighting success in the few championships that don’t have weight restrictions—not because the face predicts fighting success in itself, but because men with bigger faces are bigger overall.

Strikingly, we often found negative relations between perceived aggressiveness and fighting ability on overall win percentage (i.e., more successful fighters were perceived as less successful and aggressive). Třebický et al. (2013) noted some excellent points in their discussion section that we consider to be of importance here, one of which was postulating that human psychological systems track force output. To echo their suggestions, it could be that human psychological systems positively track knockout power but negatively track the other avenues to victory, such as submission and decision victories, leading to an overall negative association.

Overall, our results support the original Třebický et al. (2013) study in some ways but not in others. Humans may have evolved psychological mechanisms to aid in assessments of aggressiveness or competitive tendency, however they do not support the argument that structural facial cues are honest indicators of competitive ability.

Read the paper: Is facial structure and honest cue to real-world dominance and fighting ability in men? A pre-registered direct replication of Třebický et al. (2013)

When and Why We Choose Strong Men as Allies

by Mitch Brown, Donald Sacco, Nicole Barbaro, and Kelsey M. Drea

In early 2021, the common professional wrestling trope of the “stable,” a group of wrestlers with a common goal of dominance within a wrestling promotion, returned to All Elite Wrestling (AEW) with William Regal allying with Bryan Danielson and Jon Moxley. These scripted alliances have a seemingly universal understanding of how men forge bonds with each other based on perceptions of how they may aide in physical conflict. It could even be possible that these stories reflect how men have forged these alliances throughout evolutionary history. Such decisions are likely shaped by carefully navigating when (and whether) strong allies are desirable in attaining group goals.

Humans have been engaged throughout history in forming groups that facilitate goals. The process of choosing allies may have some ancestral roots. These preferences could help people identify those best suited to ensure their safety and access to resources from competitors, particularly when there could have been limited access to resources or threats of violence from other groups. People could have historically identified formidable allies to address these potential threats. Who were the best allies? Recognizing the best allies could happen through physical features that could demonstrate men’s physical prowess, given considerable research demonstrating such cues may connote actual strength. For example, men’s facial width-to-height ratio (fWHR), a configuration of facial width relative to its height, is associated with perceptions of aggression and related to their actual fighting ability.

Although perceptions of dominant personalities through fWHR are less universal than previously thought, men with a higher fWHR remain consistently perceived as more formidable and intimidating to perceivers. In fact, these perceptions offer a kernel of truth. Male professional fighters with higher fWHRs are more successful in certain aspects of combat (e.g., grappling), with archaeological records suggesting that formidable men were more likely to survive violent conflicts. These men also find themselves more prone to using aggressive interpersonal tactics.

With these (often true) stereotypes people make about men based on their fWHR, it would seem likely that people might choose high-fWHR men for physically demanding group tasks as allies – which is indeed the case for physically strenuous sports like American football. In a recent study, my collaborators and I sought to replicate these findings using a pair of tasks that could reflect, in part, realistic features of ancestral coalitional alliance, namely tug-of-war and escape rooms. In three studies, we presented participants with men’s faces that varied in fWHR, with half having high fWHRs and others low fWHRs. Our results conceptually replicated previous effects by showing that people chose men with high fWHRs more frequently for tug-of-war and were perceived as physically strong and effective in using their strength to get the job done.

Now that we knew men were chosen for strength tasks based in part on their fWHR, our next step was to know whether these preferences for high-fWHR men extend to choosing allies for protection tasks specifically. We got participants into similar competitive or cooperative mindset using a priming procedure. Then, participants chose from the same options of men’s faces as the previous studies under the assumption that they would accompany them to a football game against an historic rival of their university (in our case, Southern Miss versus Mississippi State). Knowing how football rivalries play out in the Southern U.S., that environment could get tense! When in a competitive mindset, individuals preferred men with high fWHRs over those with low fWHRs, aligning with our predictions that formidable men would be desirable for potential outgroup protection. Preferences weren’t influenced by cooperative mindset.

Nonetheless, the formidable ally could often betray his teammates for his own benefit. This potential for exploitation from the ally seems to mirror additional research suggesting a wariness to formidable men based on the possibility of the costs they could inflict. We tested this idea in a final study within this paper to determine if a competitive mindset makes the perceived threat of high-fWHR men less apparent. Using the same competitive versus cooperative mindset priming procedures described above, participants did a visual bias task that measures participants’ motivation to approach or avoid a high and low-fWHR men. Although the competitive or cooperative mindsets had no effect, people did view high-fWHR men as more threatening than low-fWHR men across under both conditions. This means that the recruitment of formidable men may reflect an “uneasy alliance” with a perceiver who may be wary of this potential betrayal.

Overall, these findings provide continued support for how historically derived perceptions of men and their physical abilities shape how people engage them in everyday environments, showing how individuals navigate social landscapes while making best estimates for the utility of their own proverbial stablemates.

Read the paper: Contextual factors that heighten interest in coalitional alliances with men possessing formidable facial structures

Can We Read Someone’s Trustworthiness in Their Face?

by Bastian Jaeger

In his autobiography, Charles Darwin recounts the time he approached the captain of the HMS Beagle. Darwin was keen on joining the crew on an upcoming trip around the world as the expedition’s naturalist, but he needed the captain’s approval. Despite recommendations by friends, the captain was reluctant at first. He thought that Darwin wasn’t cut out for the long journey – because of the shape of his nose. The captain was a strong believer in physiognomy, the idea that a person’s character is revealed in their facial appearance. Luckily, he ultimately decided to give Darwin a chance after all.

Physiognomy has a long history in scholarly thought, dating back to at least ancient Greece. Today, the idea that a person’s nose is indicative of their character may seem laughable. In scientific circles, physiognomy and phrenology (the practice of inferring character traits from skull measurements) are widely regarded as pseudoscience. But decades of research on first impressions also suggest that we are all physiognomists to some degree. We might not measure a person’s nose, but we still tend to form judgments about others based on their facial appearance. Research shows that when we meet a stranger, we immediately form an impression based on their facial appearance. This process seems to occur relatively automatically –  it only takes a few hundred milliseconds to judge whether a person seems trustworthy or not. These split-second judgments can be very consequential because people rely on them when making many important decisions. A person’s facial appearance can influence if they are hired for a job, found guilty in court, or trusted in a social interaction.

Can we actually tell how trustworthy someone is based on their facial appearance? This is what we set out to test. We were not the first to tackle this question, but previous research on the accuracy of trustworthiness impressions has yielded mixed results. Some researchers found that people can discriminate between trustworthy and untrustworthy individuals based on a facial photograph with slightly-higher-than-chance accuracy. Other studies yielded no evidence for accuracy. The plausibility of accurate trustworthiness detection has also been questioned (why wouldn’t people evolve to look trustworthy but then exploit the trust of others by acting selfishly?) and it is unclear which facial features “give away” a person’s trustworthiness.

It seems like more evidence is needed to address this question, so in a recent article, we set out to test the accuracy of trustworthiness impressions while also addressing some limitations of previous work. Misplaced trust can be consequential in everyday life. In our studies, we therefore let participants make decisions with tangible outcomes. Similar to previous studies, we let participants play a trust game. We gave some money to a sample of trustors, 131 students from the University of Zurich, who decided whether to keep the money or send it to a trustee. If the money was sent, it was tripled and the trustee had to decide if they want to split the tripled amount with the trustor (reciprocating their partner’s trust) or keep all of the money for themselves (betraying their partner’s trust). Trustors interacted with 31 different trustees, also students at the University of Zurich, and they saw a photo of the trustee’s face on each trial.

Replicating previous work, we found that trustors relied on the facial appearance of their interaction partners when deciding whom to trust. Trustees who were rated as more trustworthy-looking based on their photo were more likely to receive money from their partners. However, trustors were not able to invest their money in a smart way – they were not more likely to send money to trustees who were actually more trustworthy (those who indicated that they would return more of the money if trusted). We found similar results when analyzing how much money trustors earned across all interactions. If seeing the face of an interaction partner gives trustors a strategic advantage (because they can infer their partner’s trustworthiness to some degree) then they should be able to earn more money than a person who trusts at random. This was not the case. In fact, trustors would have earned more money by following another very simple strategy – always keeping their endowment and never trusting anyone (participants in our study turned out to be not very trustworthy).

Maybe participants didn’t send money to the trustees because they believed that they would get more in return, but because it felt wrong to signal to a stranger that they can’t be trusted? We tested this alternative explanation in another study where we simply asked participants to predict how trustworthy the photographed individuals are. We paid them when they made more accurate predictions, but again, trustworthiness judgments were not accurate. We also tested the robustness of our findings in a few other ways. Instead of showing participants cropped photos that only revealed internal facial features, we showed them the original photos that also revealed trustees’ facial structure and hairstyle. We tested detection accuracy for male and female trustees separately. We explored if trustors who are more confident in their decisions are more accurate. In all cases, we found that our participants were unable to detect the trustworthiness of their interaction partners.

Our studies suggest that modern science was right to brand physiognomy as a pseudoscience. It doesn’t seem like we can judge a person’s character just by looking at their face. First impressions may come to mind quickly, but our findings suggest that we better second-guess them. So before you trust or distrust a stranger because it feels like it’s the right decision, ask yourself what your evaluation is based on. If they simply “look trustworthy” to you, maybe find some better information first before making a decision.

Read the paper: Can people detect the trustworthiness of strangers based on their facial appearance?

HBES Early Career Award Submission Deadline EXTENDED to June 1

We are extending the deadline for nominations (self and other) for the HBES Early Career Award until June 1. The Human Behavior and Evolution Society Early Career Award recognizes individuals for their contributions to the field.


Nominations are now due by June 1 2022.


See Awards for more details, eligibility information for the Early Career Award, and the link to submit nominations (under eligibility tabs). Note: Submission are NOT extended for the Lifetime Career Award.

Differences in Men’s and Women’s Friendships Cause Some Differences in Men’s and Women’s Friendship Jealousy

by Jaimie Arona Krems and Keelah Williams

If you’ve read about Gene and his best friend Phineas in John Knowles’ great American novel A Separate Peace, the women alums of Vassar’s class of ’33 in Mary McCarthy’s The Group—or work from Elena Ferrante, Sally Rooney, or pretty much any other author describing dyadic friendships in their wider social world—you’ve read about friendship jealousy. (See also the hilarious ‘Best Friend Toast’ scene from the movie Bridesmaids.) Just as romantic jealousy protects our romantic relationships from third-party threats (e.g., partners defecting to a third party, a third party poaching our partners), we’ve found that third-party threats to our friendships can give rise to feelings of friendship jealousy. But there are some differences in how friendship jealousy plays out across sex/gender.


Of course, as with many phenomena, men and women have more in common than not when it comes to friendship jealousy. We expected—and found upon re-analyzing some of the data from our previous work in U.S. samples—that the inputs and outputs of the friendship jealousy system are the same across sex/gender. The inputs to our friendship jealousy deal primarily with the value of the friend and threat of losing the friend. That is, feelings of friendship jealousy are sensitive to the irreplaceability of our focal friend. We feel greater friendship jealousy when best friendships are threatened than when only mildly close ones are. Feelings of friendship jealousy are also sensitive to the level of ‘replacement threat’ posed by the possible interloper (the person who might steal your friend). I would feel more friendship jealousy if Joel and I always worked out together in the mornings but he started working out with his new friend James than if Joel started to spent tons time socializing with James at work, or than if Joel started spending all his time with a new romantic partner. I’m not his work pal or partner, so he’s not replacing me in the latter instances. Rather, the more the interloper stands to take my place in Joel’s social relationships, the more friendship jealousy I feel. And these feelings of friendship jealousy can cause us to engage in friend guarding—behavior aimed at helping us maintain our friendships. Again, all of this holds across sex/gender.


But in a recent article, we also raised the question of when (and why) we might see sex/gender differences in friendship jealousy.


We began from the premise that common differences in men’s and women’s friendship structures and putative historical functions affect those inputs (and outputs) of the friendship jealousy system. Insofar as these aspects affect the inputs of the system, we should expect some sex/gender differences in friendship jealousy at the prospective loss of same-sex friends. (Because sex/gender segregation in friendships is the norm from early age, we focused on same-sex friends.)


We predicted—and found in samples of U.S. community participants and students—that women report greater friendship jealousy than men at the prospective loss of best friends.


Why? First, women tend to form extremely close one-on-one friendships with one other woman, whereas men tend to form looser multi-male friendship groups. If every person got 100 friend points to invest in friends, this would be like women putting 60 points into a best friend, say, and 20 points in two other close friends, whereas men put 20 points into five friends. This structural difference implies that the value, or irreplaceability, of women’s (versus men’s) best friends might, on average, be higher.


Second, women’s extremely close best friendships are not made overnight; they take much time and effort to form. Moreover, and third, women’s (versus men’s) extremely close friendships often involve a lot of self-disclosure (e.g., which bands I like, which colleagues I hate, tales about that embarrassing time I called my advisor “mom” in a lab meeting). This information is easy ammunition. If I lose my best friend to someone else, that person might learn all my dirty secrets. So, for women, it might be both more costly to replace a best friend and more costly to lose one to someone else.


Fourth, some work suggests that male’s multi-male friendship groups are actually protective against friend loss, and that women’s dyadic friendships are more prone to breaking up—making women’s friendships perhaps more vulnerable to poaching. Indeed, girls sometimes purposefully ‘break-up’ other girls’ dyadic best friendships to poach one of the newly-on-the-market friends, but we knew of no such attacks among boys’ friendships.


We could make a strong prediction that, when faced with their best friends becoming potentially closer to another friend, women might report greater friendship jealousy than men. And they did.


Our next two predictions, focusing on men, were more tentative. First, male (but not female) primates seem to have a long history of banding together in intergroup violence. The relative size of one’s coalition plays a gargantuan role in such conflicts. It’s possible, then, that for men even peripheral allies (e.g., acquaintances) would be somewhat valuable. That is, just as women might value a same-sex best friend more than men do, men might value a same-sex acquaintance more than women do. The size of the effect is small, but we do find that men report greater friendship jealousy at the prospective loss of same-sex acquaintances than women.


Second, this same logic suggests that contexts of intergroup conflict might amplify the value of men’s allies. Thus, we designed an experiment wherein some participants were told to imagine that their same-sex friends were also teammates with whom participants would face off against an opposing team. Moreover, these teammates were not only becoming potentially closer to another friend, but also to the opposing team. (Other participants were asked to imagine friends becoming closer to one’s same-sex rival.) We predicted and found that the intergroup conflict context amplified men’s reported friendship jealousy (at the prospective loss of friends-cum-teammates to rival teams). Again, though, this effect was small.


In all, the structures and perhaps historical functions of men’s and women’s friendships can bear on the inputs to the friendship jealousy system. For example, if I put most of my friendship eggs into a single best friend basket (versus multiple close friend baskets), it makes sense for me to be very sensitive to detecting and responding to threats to my best friend. By affecting these inputs—like the irreplaceability or value of the focal friend—these sex/gender differences in friendship seem to translate into some sensical sex/gender differences in friendship jealousy.


Read the paper: Sex (similarities and) differences in friendship jealousy

Rules of Descent Only Affect Women’s Marital Dispersal

by Ting Ji

Sex-biased dispersal is a widespread phenomenon in animals and humans. Different species show marked contrasts in the patterns of sex-specific dispersal. As for humans, we use the social norms of post-marital residence to regulate sex-specific dispersal at marriage. In most human societies, women leave their natal households and live with their husband’s kin (i.e. parilocality). However, neolocal residence is more popular in industrial societies, i.e. men and women form a new family separate from the kin of either side. Less common patterns include matrilocality, where men move to wife’s household, or ambilocality, where men and women can live with either side of the kin. In a few human societies, such as Mosuo in Southwestern China, the residence is duolocal (or natallocal), where neither men nor women disperse at marriage, husband visits his wife’s household at night, and returns home in the morning. In this society, both men and women live with their close relative for their entire lives. Patterns of sex-biased dispersal structure populations and determine whether an individual is surrounded by relatives or unrelated group members, and thus play an important role in shaping social behaviors.

What predicts the differences in sex-biased dispersal patterns in humans? Anthropologists have long noticed that there is correlation between different social structures in many regions. More specifically, patrilocality is usually associated with patrilineal descent, and matrilocality is associated with matrilineal descent. In other words, in patrilineal societies, descent is traced along male lines, men are more likely than women to remain in natal households, and women are more likely to marry out. In matrilineal societies, descent is traced through female lines, the opposite pattern thus can be found. Is there, however, a causal relation between these two types of kinship norms? Murdock has argued that certain descent systems might arise from different patterns of post-marital residence, i.e., changes of residence drive the change of descent. However, phylogenetic comparative studies show that co-evolutionary trend between these two cultural traits varies in each language family. Different mating systems and local competitions have been proposed to influence sex-biased dispersal as well.

Sex-biased dispersal in humans is also affected by ecological factors. Earlier studies have described dispersal patterns vary in populations with different modes of subsistence. In many hunting, gathering, and fishing societies (foragers), there is no strict rule about which sex should remain and which sex should disperse. Couples often change their residence from time to time. While in horticulture societies, both female-biased and male-biased dispersal are found. Dispersal patterns in pastoralism and agricultural societies, however, are overwhelmingly female-biased. The association between sex-specific dispersal and mode of subsistence has led to the hypothesis that the transition from foraging to agriculture and/or animal husbandry is likely to have promoted female migration. However, the evidence is mixed, with some research finding that the emergence of intensive agriculture, plow agriculture, or large domestic animals hindered matrilcoality and other research suggesting a male-biased dispersal system during the period of the introduction and intensification of agriculture.

As one of the largest language families, the evolutionary history of sex-biased dispersal in Sino-Tibetan has attracted much attention. However, archaeological and genetic studies provide mixed conclusions, and there is still much debate. Moreover, sex-specific models are needed to fully understand the evolution of human dispersal, as post-marital residence and sex-specific dispersal are not always interchangeable. Here we studied the evolutionary history of dispersal norms for males and females in Sino-Tibetan populations, using cultural phylogenetic comparative methods. And we also tested the coevolution of sex-specific dispersal and descent and subsistence.

We collected and analyzed ethnographic data on kinship norms and subsistence from 97 Sino-Tibetan populations. As in many other places around the world, women disperse and men remain in over 85% of the studied Sino-Tibetan populations. Women do not disperse at marriage (as in matrilocal or duolocal residence) in about 5.2% of all societies, whereas approximately 9.3% of the societies lack of strict norms on whether women should disperse or not.

We found that kinship descent likely co-evolved with female dispersal, but not with male dispersal. These findings suggest that in patrilineal societies, dispersal patterns for men are quite flexible, they can choose to move or remain in their natal households. Nevertheless, there is strict control over women’s dispersal. Our results also show that the state of “patrilineal/female disperse” is very stable, and women are unlikely to change their dispersal strategy in patrilineal societies, unless descent changes first.  We also found that female dispersal was likely ancestral, implying that the rare duolocal residence in Mosuo population, in which neither sexes disperse, evolved later. This result is consistent with an earlier genetic study suggesting that the Mosuo might have adopted matriloclaity recently. Furthermore, we found agriculture likely co-evolved with only female dispersal patterns, but the result is sensitive to alternative coding strategy. And we did not find association between domestic cattle and dispersal patterns of either gender. Our results thus illustrated how subsistence or descent can play different roles in shaping male and female dispersal behavior.



Read the paper: A phylogenetic analysis of dispersal norms, descent and subsistence in Sino-Tibetans

HBES 2022 Seeking Volunteers for Conference Support

#HBES2022 Still Virtually Everywhere conference is seeking volunteers from around the world to provide tech support, loading talks for speakers and moderating live Q&A after each talk.

HBES is offering a year’s free membership to volunteers.

Volunteers will receive training in using the platform.

Anyone interested should send the host, Leif, a message ASAP to

#HBES2022 Important Dates & Information

The host and program committees of #HBES2022 are excited to engage our members in an action-packed, fully customized, online conference experience. Here, you will find all of the information you need to join us (Still) Virtually Everywhere this summer!

HBES 2022 will take place June 22 – June 25. Specific time blocks will be announced soon

The conference will be open to only HBES members and registration will be FREE. You must still register for the conference using the registration form that will open June 1. If you’re not currently a member, please join or renew asap.


HBES Virtually Everywhere will be hosted on the ohyay platform and is a fully-customized online conference where you can 1) grab a coffee with colleagues before heading to a talk, 2) sing karaoke with your friends, or 3) discuss future collaborations at the hotel bar!

For the best virtual experience, we recommend all attendees use Chrome on a plugged-in computer, and strongly encourage the use of headphones so that everyone has a better auditory experience.

We look forward to seeing you all!

If you have questions, please contact the host and program chairs using this form.

Please bookmark the conference webpage for the most up to date information.


Mark your calendars! Here are the important dates you need to know:

  • Abstract submissions opens: April 15th, 2022 (limit one first-author submission per person of any type)
  • Review of abstract submissions will begin on a rolling basis: May 1st, 2022
  • Registration opens: June 1st, 2022
  • Abstract submission deadline and deadlines for New Investigator and Post-Doctoral awards: May 15th, 2022
  • Final abstract acceptance confirmation date: June 1st, 2022
  • Early Registration deadline: June 15th, 2022
  • Late Registration deadline: June 21st, 2022

Call for 2022 HBES Awards Open Until May 1

The Human Behavior and Evolution Society Early Career Award and Lifetime Career Award recognizes individuals for their contributions to the field. We are soliciting nominations (self and other) for each award.


Nominations are due by May 1 2022.


See Awards for more details, eligibility information for each award, and links to submit nominations (under eligibility tabs).