HBES 2024 member survey – summary of findings

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Human Behavior and Evolution Society Post-Conference Survey 2024

In 2024, we sent out a survey to the HBES mailing list (>1700 recipients) and everyone who attended the 2024 HBES Conference in Aarhus, Denmark. The descriptions of survey results are organized below into:

  1. Respondent information
  2. HBES in general
  3. Aarhus conference
  4. Future conferences
  5. Spending priorities

 

  1. RESPONDENT INFORMATION

107 members responded to the survey. Their information is tabulated below according to their academic status, discipline, and region:

  1. SATISFACTION WITH HBES

Based on survey participants’ Likert responses (see figure below), few were dissatisfied with HBES in general. The quality of our journal received the most praise while Elsevier received the most criticism.

 

Few participants provided additional comments. Among those who did, there was disagreement with respect to whether HBES is too political or not political enough, and whether HBES is not doing enough to encourage inclusivity or is doing too much; perhaps this reflects a healthy diversity of opinion within the society. Concerning HBES’ communication efforts, several participants encouraged HBES to be more actively engaged in social media or other outlets, to correct misinformation regarding our research or regarding evolutionary approaches to cognition and behavior in general – both time-intensive tasks. Other participants wanted more timely and transparent communication from the executive council, concerning the society’s financials or the timing and location of annual meetings.

Finally, several members wanted greater diversity on the executive council and in society and conference awardees. Please remember to nominate individuals for these positions and awards (please see recent emails regarding nominations for awards and elected positions).

 

  1. AARHUS CONFERENCE

Survey participants overall felt the Aarhus conference was a success, and on several metrics the majority of participants felt the conference was above average (see Figure below).

Most respondents felt that sexual harassment was not a problem (51/59) or was the same or less of a problem than at other conferences (7/59).

 

  1. FUTURE CONFERENCES

Most survey participants were against future conferences that are either fully online or combine online and in-person. 94 of the survey respondents indicated months they were available or preferred for future conferences (see Figure below).

 

 

  1. SPENDING PRIORITIES

Members were asked about their agreement as to whether HBES should be funding various concerns and also whether they would take advantage of such funding.

Given the major decline in royalties that HBES now receives from Elsevier—formerly HBES’ chief source of funding—the executive council will be prioritizing funding of HBES conferences over local events or preconferences at other conferences in the foreseeable future.

 

Is there information that you think the HBES executive should collect about its members or their opinions? Let us know by contacting the HBES Communications Officer.

A couple being watched by a lone man and a lone woman

Mate-choice copying is a sex-general heuristic among humans

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– by Robert Bowers

There is a large ground bird from the American plains whose mating system could not be more convenient for studying sexual selection. Over a conveniently short mating season, male sage grouse gather in a conveniently compact space, within a few miles of each other, and there they all perform their best mating displays. The hens of this species browse the performances at their leisure and choose a mate. This event attracts not only competing cocks and broody hens, but also biologists keen on showing how the striking sexual dimorphisms expressed in this species relate to female choice and intersexual sexual selection. Unsurprisingly, mating variance among male sage grouse is large, and optimism was high that with enough clipboards, the exaggerated waddles and dances and girth of these males would all have a clear explanation. But the mating variance was too great. Even with all the elaborate male characters of these birds, there were still insufficient bases to explain the extent that some hens chose the most successful males. In apparent exasperation, there is a remark in the middle of a 1960’s doctoral thesis that the females might be copying each others’ choices.

The subsequent area within sexual selection research, initially termed “female copying”, grew in several ways. Theoreticians showed its relation to reproductive variance and sexual selection. Experimentalists demonstrated it empirically in laboratory demonstrations. And phylogenetically, it grew in the breadth of species that were shown to be affected. However, even with all these advances, it remained within the theoretical context of female choice, and continued to be studied as if it were an exclusively female phenomenon. Even among humans, a species in which both sexes choose, a large majority of “mate-choice copying” (what the phenomenon is now called) studies focused exclusively on females choosing males.

Among humans, however, the earliest documented recognition of mate-choice copying (in a dating advice column from 1928, predating the sage grouse observation by decades), was actually about men copying the choices of other men. Indeed, studies that have included both men and women have most often found that both sexes are affected by the choices of others. Despite this, it remains common to find mate-choice copying presented as a specifically female phenomenon. Typically, this sentiment is accompanied with reference to Parental Investment Theory, the popular view that the sex that suffers greater costs in reproduction will have greater use for any means of choosing better mates. The received view is that women should engage in social mate choice heuristics more than men.

But mate choice is complicated, and harnessing information about mates from attending to others’ choices is no less so. When one considers mate-choice copying more closely, several features of social mate-choice information (as well as of human parental care) muddy the theoretical waters that motivate looking for a sex difference. Mate-choice information is readily accessible, relevant to both sexes, indicative of characters not visible on the surface, and fallible. Copying others’ choices heightens competition. Paternal care among humans is long and extensive. All of these features push expectations in various directions about what kind of sex difference should or should not express in how people attend to others’ choices when choosing a mate.

Not long ago, we decided to address this question directly. One problem in assessing sex difference claims from previous data was that male and female participants are typically presented with different stimuli. Male mate choice is assessed with images or videos of women, and female mate choice is assessed with images or videos of men. And one point that has been clear from the earliest human mate-choice copying studies is that the specific stimuli matter; the strength of the effect depends heavily on such features as the relative attractiveness of the stimuli employed.

To address whether the sexes differ in the extent that they rely on social mate-choice heuristics, we removed all sex-specific stimuli so that we could present the very same stimuli to male and female participants. Profiles furthermore included only accurate information about real daters making sincere choices in the context of a speed-dating event.

Our results did not support the kind of sex difference expected by the received view. We did find evidence of human mate-choice copying, but both male and female participants changed their ratings in the direction of others’ choices, and to comparable extents.

This matters because mate-choice copying is both a cause and a consequence of sexual selection. As a consequence, it being sex-general implies that there is substantial pressure on both sexes to be selective. As a cause, the sex-generality of mate-choice copying is expected to have the effect of increasing reproductive variance, and so of intensifying selection on sex-specific characters in both sexes.

These results add human mate-choice copying to the growing list of phenomena that do not abide expectations of the still dominant set of views related to Parental Investment Theory, Sexual Strategies Theory, and Bateman’s Principle. These views satisfy aesthetically but are increasingly found to falter empirically, not necessarily because they are wrong, but because mate choice is complicated, and because human mate choice and parenting are not so one-sided as in the comparatively extreme mating systems amid which these ideas were developed. The good news is that with attention to the specific features of the structure of the problem mate seekers face, there are fine grounds for refining understanding of sexual selection in the context of how copying others’ choices allows mate seekers to harness social information about mate quality.

Read the original article: Bowers, R.I., Pinar, V., Sariyildiz, S.S., & Parlak, D. (2025) Is mate-choice copying a female phenomenon? Evolution & Human Behavior, 46(1), 106653.

Do long-term relationships help explain human sexual dimorphism in upper-body strength?

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– by Caroline B. Smith & Edward H. Hagen

Humans are sexually dimorphic, meaning there tend to be differences between men and women on traits like height and weight. In our study we focused on the sexual dimorphism in muscle mass: men have more muscle mass than women. Why? The standard story is that higher male strength leads to more sexual partners, leading to sexual selection on male upper body strength. Previous research found that higher male muscle mass was positively associated with more sexual partners and lower age at first sex, supporting the sexual selection hypothesis. That study also found that higher strength comes at a cost, specifically decreased immune function and higher energy needs.

However, past research did not investigate women. The sexual selection hypothesis predicts no association between women’s strength and mating success, because partner numbers are not thought to be related to women’s fitness in the same way they are for men’s. We tested the prediction from the sexual selection hypothesis that the association of upper-body strength, proxied by grip strength, with mating success is significantly positive for males and significantly less so for females. We also tested for tradeoffs of upper-body strength with immune function and nutritional intake.

In our study, we used two large independent representative samples of US adults, collected by the National Health and Nutrition Examination Survey (NHANES) in 2011-2012 (N=2853) and 2013-2014 (N=3244). In studies of human behavior, it is important that hypotheses are clearly specified prior to statistical analysis to prevent “fishing” for statistically significant results. To do this, we first conducted an exploratory pilot study using the data from 2011-2012. We used these data to refine our models and predictions, and then tested them in data from 2013-2014 which we had not observed.

We used four proxies of mating success as our model outcome variables: Number of lifetime sexual partners, number of sexual partners in last year, age at first sex, and being currently partnered (True/False). We used grip strength as our main explanatory variable as a proxy for upper-body strength. We also controlled for five groups of possible compounds including anthropometrics (e.g. height and weight), physical activity (e.g., vigorous recreation), socioeconomic factors (e.g., education, ethnicity), hormones (i.e., testosterone), and health factors (e.g., chronic illness, depression). We tested for tradeoffs of strength with immune function (white blood cell count) and energy and protein intake.

We found mixed evidence for the sexual selection explanation overall. In models of current partnered status, we found a significant interaction of strength and sex such that stronger men, but not stronger women, were more likely to be partnered, consistent with sexual selection. But no such significant interaction emerged in models of lifetime sexual partners—stronger men and stronger women both have more lifetime sexual partners contrary to the sexual selection hypothesis. We found no consistent association between strength and either age at first sex or number of past-year sexual partners.

We found positive associations of strength with protein and energy intake for both sexes. We found no significant association of strength with immune function, perhaps because we controlled for height, which was negatively associated, suggesting a tradeoff.

The stronger association of grip strength with partnered status for men than for women is consistent with a role for sexual selection in sexually dimorphic upper body strength, perhaps via female choice for long-term relationships with more productive mates.

It is not clear why women’s strength would be positively associated with sexual partner numbers. It could be that there was selection for more formidable men to prefer more partner variety, and stronger women have a similar preference as a byproduct of selection on men. It could be that there is assortative mating on strength: if stronger men are motivated to switch partners more frequently, their (stronger) mates would also likely have more mates. It might be that stronger women require less male investment, or can take more physical risks, and so instead benefit from greater partner numbers through, e.g. genetic bet hedging, forging relationships with multiple males, ability to conduct a more extensive search for a high-quality long-term mate, or through avoiding or leaving costly long-term partnerships. It might be the case that there are some sex-specific confounds that we failed to control for, or that our models are otherwise misspecified. There also might be reverse causation, e.g., women who are interested in greater partner variety keep in better shape. The sexual selection hypothesis also might be wrong. Or these results might simply be noise.

There were some limitations to our study which are important to note. The data we analyzed for our study are cross-sectional data, meaning we cannot infer causal relationships between variables. Participants self-reported their sexual behavior, including their numbers of sexual partners, and might have either accidentally or purposefully reported their behavior inaccurately. This study used data from the US, where widespread access to contraceptives uncouples reproductive success from mating behavior for both men and women. In addition, we removed 68 participants with 100 or more lifetime sexual partners on the grounds that these might involve evolutionarily novel patterns of behavior that would not conform to predictions of the sexual selection hypothesis.

In conclusion, the sexual selection hypothesis was clearly supported for the positive association of male strength with the probability of being partnered, but not for lifetime number of sexual partners which had a positive relationship with strength for both men and women. We found no consistent association between grip strength and age at first sex or number of past-year sexual partners.

We argue that in human evolution, men likely increased their fitness, not by obtaining additional sexual partners, but mostly by investing in long-term relationships and offspring, and reaping the efficiency benefits of a sexual division of labor. Our results suggest that, for human males, high upper body strength helps obtain a long-term partner through female choice, perhaps due its advantages in provisioning resources through big game hunting and providing protection, and in male-male physical competition.

Read the full article here: Smith, C.B., & Hagen, E.H. (2025). Strength, mating success, and immune and nutritional costs in a population sample of US women and men: A registered report. Evolution & Human Behavior, 46(1), 106647.

A woman having an ultrasound

Looks just like daddy: Investigating perceptions of fetal resemblance

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– By Carlota Batres

When it comes to children, women can be certain that a child is theirs, but men cannot. In other words, there is always some chance that another man fertilized the woman’s egg. The estimate of children who have genetic fathers different from their alleged fathers is between 1%-3%.

One of the sources of information that men use to determine the likelihood of being the genetic father is perceptions of the child’s physical similarity. Research has found that fathers who perceive that their children resemble them invest more in those children, for example by spending more time with them and by having more supportive/engaged parenting.

In our study, we aimed to examine whether mothers having an ultrasound would claim that the fetus looks more like the father. Even with such limited visual information, we predicted that mothers would be more likely to say that the fetus resembled the father in an effort to assure paternity.

In addition to perceptions of the child’s resemblance, men also use information about their partner’s faithfulness and trustworthiness to determine how likely they are to be the biological father. For instance, one study found that men’s perceptions of their partner’s fidelity predicted their parental investment. Marriage is one way in which couples pledged faithfulness to each other. Indeed, while infidelity takes place in married couples, the incidence of cheating is much lower than it is in unmarried couples. Therefore, for our study, we also aimed to examine differences between parents who were married and parents who were not. We predicted that among unmarried parents, mothers would be even more likely to say that the fetus resembled the father.

Participants were recruited at an obstetrics and gynecology clinic, mostly during their routine 20-week pregnancy ultrasound. If they decided to participate, they were given a questionnaire and then called in for their ultrasound. Once the fetus was visible in the 2D imaging, if the biological mother and the biological father were in the ultrasound room (as per the participants’ questionnaire responses), the ultrasound technician would ask them “Who do you each think the baby looks like?” and would record their answers.

We found that fathers were just as likely to say the fetus resembled themselves (49%) as they were to say that the fetus resembled the mother (51%). However, mothers were significantly more likely to say that the fetus resembled the father than to say that the fetus resembled themselves. In fact, 26% said that the fetus resembled themselves and 74% said that the fetus resembled the father. Moreover, mothers who were not married were even more likely to say that the fetus resembled the father than married mothers. More specifically, 93% of unmarried women said that the fetus resembled the father.

Evidence from our study supports the hypothesis that mothers should be more likely to say that the fetus resembles the father. If the fetuses actually did resemble the fathers, the fathers should also be more likely to say that the fetuses look like them. However, we did not find this to be the case. Rather, we only saw this effect with mothers, suggesting that the unconscious bias in mothers’ observations about similarity to the fathers does not reflect actual resemblance. This is supported by other research which has found that when unrelated participants were asked to match photographs of parents to newborns, they were more accurate in matching the mothers than the fathers.

In conclusion, our study provides evidence that even with extremely limited visual information, mothers have a bias toward claiming paternal similarity. This bias is likely an adaptation that helps the mothers secure investment in their unborn children since fathers who believe that their children resemble them invest more in those children.

Read the original article: Batres, C., Mullen, A., Krofl, S., & Trainor, L. (2025). Investigating perceptions of fetal resemblance. Evolution and Human Behavior, 46(2), 106670.

The Balancing Act of Life: How Having Children Historically Affected Lifespan in Rural Spain

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– By Ángel Luis González Esteban & Francisco Marco-Gracia

For centuries, scientists have pondered a fundamental question: is there a biological trade-off between reproduction and longevity? In simpler terms, does having more children mean a shorter lifespan for mothers? This is a core idea in evolutionary theory, suggesting that bodies have limited resources, and investing heavily in having offspring might leave less for maintaining the mother’s health and extending her life.

While this idea has been supported by studies on animals, the picture in humans has been less clear, with many studies yielding conflicting results. This is often because it’s challenging to disentangle evolutionary factors from the complex mix of genetics, environment, and societal influences that shape human lives.

To shed more light on this, we delved into the rich historical records of rural Spain, specifically parish registers from 17 villages, spanning a remarkable five centuries, from 1536 to 1965. This allowed us to examine the lives of over 5,000 women, meticulously tracking their fertility and longevity, and even accounting for the experiences of their parents. This long-term perspective and the ability to consider intergenerational patterns are what make our study particularly valuable.

What Did the Data Reveal?

Our analysis revealed some fascinating insights into the historical relationship between motherhood and lifespan in this rural Spanish population:

– More Children, Shorter Lives: Overall, we found a significant negative impact of the number of children a woman had on her longevity. On average, each additional child was associated with a reduction in the mother’s lifespan. Having a large family (8 or more children, which was above average for any period in our study) was also clearly linked to reduced longevity. This suggests that the biological costs of pregnancy, childbirth, and potentially the demands of raising a large family did take a toll on women’s bodies over the long term.

– The Impact of Surviving Children: Interestingly, the number of children who survived past the age of five had an even stronger negative association with the mother’s lifespan. This highlights that the physical demands of childcare and breastfeeding likely played a significant role in the wear and tear on mothers, beyond just the act of pregnancy itself. Even considering that mothers with more children might have received more support, the negative effects on their longevity seemed to outweigh any potential benefits.

– The Timing of Motherhood Mattered: Having a first child at a very young age (before 25, and especially before 20) was associated with shorter lifespans. This could be because early motherhood, especially in a time of limited resources, placed a greater strain on still-developing bodies and was often linked to longer reproductive periods. Conversely, having the last child after the age of 40 was linked to increased longevity. This might seem counterintuitive, but it likely reflects that women who were healthy enough to conceive and carry a pregnancy to term at a later age were already predisposed to longer lives.

– The Pace of Reproduction: We also looked at birth intervals and the total length of a woman’s reproductive life. While the average time between births didn’t show a strong link to lifespan on its own, women with a long reproductive span (over 15 years) combined with consistently short birth intervals (what we termed “natural fertility”) lived significantly shorter lives, on average about 1.5 years less than others. This suggests that insufficient recovery time between pregnancies could accelerate aging.

– The Shift with Modernity: When we compared the pre-industrial period to the time after the onset of fertility control in the late 19th century, some patterns changed. For example, the number of surviving children became a more significant factor in the later period, likely due to lower child mortality rates meaning mothers spent more years actively raising their offspring. Notably, the negative impact of having children very early or very late seemed to lessen after the fertility transition, possibly due to changes in family planning and improved healthcare. The reduction in the overall reproductive period in more recent times appears to have been a key factor in improving women’s longevity.

– Nature vs. Nurture: We also considered whether these patterns could simply be due to inherited traits – perhaps long-lived women came from long-lived families and had fewer children due to genetic or culturally transmitted behaviors. However, even after accounting for the longevity and fertility of the women’s parents, our core findings remained consistent. This strengthens the idea that there was indeed a trade-off between fertility and longevity driven by the biological costs of reproduction.

Implications for Today

While our study focuses on historical populations with vastly different living conditions and healthcare access than today, it provides a valuable long-term perspective on the fundamental biological trade-offs that women have faced. The dramatic increase in women’s lifespan in modern times is undoubtedly linked to factors like improved nutrition, healthcare, and, crucially, the ability to control fertility, allowing for greater biological recovery between pregnancies and a shorter overall reproductive window. Our research underscores the profound impact that reproductive decisions and environmental context have on women’s health and longevity across generations.

We hope this glimpse into our research has been engaging. We believe that understanding the historical interplay between fertility and longevity can offer valuable insights into human biology and the remarkable changes that have shaped our lives over the centuries.

Read the original article: Marco-Gracia, F.J., & González Esteban, Á.L. (2025). Live fast, die young, leave a good-looking offspring: longevity and reproduction tradeoffs in rural Spain (1536-1965). Evolution & Human Behavior, 46(2), 106673.