Does high infection risk influence casual sex attitudes, desires, and behavior? These results may surprise you.

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– by Jessica Hlay & Carolyn Hodges-Simeon

March of 2020 remains a memorable time in most people’s lives. Few will forget the breakout of COVID-19 and resulting pandemic: cities were shut down, people were quarantined, homes were locked, and fear of infection was at an all-time high. However, news programs started showing a different picture in some areas: large groups of university students did not cancel spring break trips. Instead, people drove en masse to beaches, partying as usual, undoubtedly sharing drinks and breathing each other’s air. A disease transmission nightmare. This scenario reveals the inherent trade-offs between two fundamental evolutionary goals: health management and reproduction. Under what circumstances to people choose reproduction over health? Or vice versa? Is it possible that the chance of sex and socialization is great enough to override an adaptive disease avoidance response, especially in young, healthy adults?

One of the ways that we measure differences in people’s health-protective behavior is through disgust sensitivity. It is defined as an individual’s sensitivity to infection-related stimuli. It affects what we touch, consume, and with whom we interact — for example, those with higher disgust sensitivity are more likely to avoid things they find disgusting and feel more anxious about interacting with strangers. Reproduction is risky from an infection standpoint — sexual activity, by nature, involves close contact.

Our research team decided to explore whether an individual’s disgust sensitivity is related to their sociosexuality (also known as, attitude, desire, and behavior towards casual sex). Previous research led us to believe that we would find results supporting our hypothesis, such that increased disgust would be associated with decreased interest in casual encounters. However, we noticed a few gaps in previous studies exploring this question: 1) Disgust sensitivity has many domains (pathogen, sexual, and moral), however previous studies only gauged the relationship between sexual disgust sensitivity and sociosexuality. Since we’re interested in how pathogen risk relates to casual sex, we included all domains of disgust in our study. 2) Sociosexuality also has three domains (attitude, desire, and behavior), however previous studies only explored composite sociosexuality scores, limiting our understanding of the relationship between each of the three domains and disgust (e.g., does disgust affect sociosexual attitude more than behavior?). And finally, 3) most studies only collected responses from the United States, or their sample demographics are not reported. Since disgust sensitivity and sociosexuality are thought to be at least partially influenced by culture, economic development, and environment, we sought to include a wide range of countries in our samples. Additionally, with the help of online data collection, we were able to collect samples before and during the COVID-19 pandemic.

Using an online survey platform, we conducted a study including data from four different timepoints and in 22 countries. In our survey, participants provided demographic information and responded to the Three Domains of Disgust Sensitivity Scale and the Sociosexuality Orientation Inventory-Revised Scale. We then conducted tests to assess our main question: How does each domain of disgust sensitivity (i.e., pathogen, sexual, and moral) predict each domain of sociosexuality (i.e., attitude, desire, and behavior)? We included all domains of disgust in our model to account for their shared variance, as well as age, sex, and country.

Several of our findings were just as predicted: sexual disgust negatively predicted sociosexuality overall. That is, the more sexually disgusted someone was, the less open to casual sex they were. Specifically, sociosexual attitude seemed to be the driving domain of this relationship. In addition, women and older adults showed higher disgust sensitivity than men and younger adults. These findings were consistent across diverse countries.

However, we found some surprising results when we examined the association between pathogen disgust sensitivity and sociosexuality. Interestingly, pathogen disgust positively predicted composite sociosexuality and sociosexual attitude, opposite of our prediction. Also opposite of our predictions, sexual disgust positively predicted sociosexual behavior. We found this in both pre- and post-COVID samples. These results suggest that those with greater pathogen disgust (holding other domains of disgust constant) are more open to casual sex and the more they engage in it. In other words, if you are low in sexual disgust, a pandemic may make you *more likely* to seek out casual encounters (and all the more if you are young and/or male). This accords with our observations of those young adults who seemingly put themselves at great risk to party on a beach in Florida.

Evolutionary theorists may be quick to challenge such a counterintuitive finding — that is, what is the benefit of increasing sexual content when infection risk is higher? While still unclear, one useful theoretical model may be the “bet-hedging” hypothesis. Like the Red Queen Hypothesis, this idea builds on the knowledge that offspring genetic diversity is a powerful intergeneration weapon against pathogens. That is, individuals can diversify their offspring by engaging in multiple mating. While much more research is needed to understand the costs and benefits of less restricted sexual behavior under pathogen threat, these findings suggest it could be a fruitful avenue of study.

Read the original paper: Hlay, J., Albert, G., Batres, C., Waldron, K., Richardson, G., Placek, C., Arnocky, S., Senveli, Z., Lieberman, D., & Hodges-Simeon, C. (2022). Disgust sensitivity predicts sociosexuality across cultures. Evolution and Human Behavior, 43(5), 335-346.

How economic inequalities affect mating markets, and how they might shape culture

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– by Rob Brooks, Khandis Blake & Lutz Fromhage

Choosing a mate involves a vast number of considerations. Personalities, looks, kindness, and attentiveness all come into play. So do status, wealth and material resources because mating partnerships are – at least in part – economic arrangements.

A couple shares much of their time, labour, and wealth, often investing in their joint social mobility and in raising children. Wherever and whenever money and status matter in heterosexual mating decisions, it is far more common for women to partner upward (a pattern called hypergyny) than it is for men. Across cultures and eras, hypergyny is common but its opposite (hyperandry) is vanishingly rare.

If economic considerations influence mating decisions, then it seems reasonable to expect the distribution of wealth to have important effects on mating patterns. For example, gaps in average income or wealth between women and men will likely alter the number of suitable partners a person might encounter. When women have few means of their own, then a majority of men could provide at least some upward mobility to any one of a majority of women.

That’s an argument we have encountered in verbal form, but when we wanted to make the argument in our work on the mating market consequences of inequality, we found a surprising lack of modelling. Moreover, thinking about the effects of income inequality within the sexes was even more sparse. If economic conditions like gender- and income inequality affect mating prospects, then that’s one more reason for them to also affect individual well-being, happiness, and political attitudes. So, in a recent Evolution and Human Behaviour paper, we modelled how inequalities between women and men, and inequalities within the sexes, might influence fitness prospects under hypergyny.

The model

We created a population of individuals (a million of each sex), assigning them ‘wealth’ according to specified sex-dependent distributions. Their ‘status’ is their rank-order in wealth within their sex, so we can compare what happens under various wealth distributions. Individuals go through a series of one-to-one encounters with random unpaired members of the opposite sex. If, in an encounter, the two individuals’ preference rules are met, they form a pair and don’t participate in any further encounters. The result that interested us was how sex and status influenced the chances of an individual pairing up within 100 encounters.

The simplest preference rule – Choice Rule 1 – considered an encounter a match if the man’s wealth was the same as or greater than the woman’s. Some might find men’s lack of agency and women’s hard-edged preferences somewhat affronting, so we tried a few other rules. Rule 2 only allowed a match if the man’s wealth exceeded the women’s but by no more than a specified ‘cap’. Rule 3 added a second trait (which we imaginatively called ‘X’) that men cared about in that they only paired with a woman whose X exceeded their own. And Rule 4 gave women and men both preferences for wealth and ‘X’. Rules 2 to 4 made the results of our modelling a little less stark, as one might expect, but not fundamentally different, so our paper focuses really on the original preference rule 1.

Inequality between the sexes

If the wealth distribution for women doesn’t differ from that for men, the result is simple and easily anticipated. Men of above average wealth always find a match, the poorest never do, and the success of those in between depends on where they fit in terms of ranked wealth (i.e. ‘status’). In the same way, women of below average wealth always find a man who meets their preference and the wealthiest never do. The result is so obvious it probably doesn’t need modelling, and the intuition is common among evolutionary scientists, at least as far back as Trivers and Willard’s 1973 paper about adaptive offspring sex ratio adjustment.

Things get a bit more interesting when we introduce a small sex difference in mean wealth. If men average one standard deviation more wealth than women, the chance of mating improves dramatically for below-average status men and above-average status women (remember the above-average men and below-average women were already successful in pairing).

We modelled the effects of sex differences in mean wealth for up to four standard deviations in each direction, and showed that the more men’s wealth exceeded women’s, the more likely poorer men and wealthier women were to find a mate. When women’s wealth exceeded men’s on average, it was the above-average men and the below-average women whose mating prospects declined.

These results provide some insight into the mating market consequences of gender gaps. Those consequences might alter how people approach mating, gender relations, and even voting. For example, Incel (involuntary celibate) men, many of whom are young and below average income, blame narrowing gender gaps for undermining their marriage and mating prospects. They are infamous for their often violent, misogynistic rage, much of it directed at movements like feminism and laws that limit gender inequities.

Income inequality

Next we turned our attention to within-sex income inequality by altering the standard deviation of the distribution of wealth within each sex. We began by manipulating inequality in the same way for women and men simultaneously. Reducing inequality improved the pairing success of the two groups that struggle most finding a partner under hypergyny: the poorest men and wealthiest women. These results match with the intuition that – under hypergyny – inequality leaves a larger number of poor men unable to find a mate, and likewise that very wealthy women will be unable to find a partner whose income exceeds theirs.

An increase in inequality, however, did not hit the poorest men and wealthiest women as hard as it hit those men who were just below average in wealth and those women who were just a bit wealthier than average. If our modelling holds up in real mating markets, it would suggest that mating markets might respond to inequality in ways that entail more than merely comparisons between wealthy and poor.

That becomes even more true when we manipulate the inequality in one sex alone, while keeping it constant in the other. Those details are probably beyond a readable blog post, but the most intriguing finding is that a small shift in status can make a big difference between whether inequality suits or harms one’s mating interests..

Where to from here?

Evolutionary behavioural scientists have long understood that mating markets can have profound effects on a variety of behaviours. This enterprise has been most successful, to date, in the study of biased sex ratios and their flow-on effects. Nonetheless, economic inequalities are known to be associated with behaviours that are related to mating, as documented in Martin Daly and Margo Wilson’s extensive research on homicide rates. Indeed, our recent studies of self-sexualisation on social media, and the incidence of Incels posting on Twitter, drew to our attention the need to model how inequalities affect mating markets.

Our model shows that the effects of inequalities on mating interests are never as simple as favouring one sex at the expense of the other. It is our hope that our paper stimulates both theoretic and empirical exploration of how economic inequalities between and within the sexes shape mating markets and a variety of human behaviours.

Read the original paper here

Brooks, R.C., Blake, K., & Fromhage, L. (2022). Effects of gender inequality and wealth inequality on within-sex mating competition under hypergyny. Evolution and Human Behavior, 43(6), 501-509.

Across 42 countries, how did the unique social circumstances of COVID-19 affect fundamental social motives?

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– by Cari Pick

For many people worldwide, the COVID-19 pandemic created an evolutionarily novel set of pressures: extended social isolation as 57% of the world’s population was confined to full or partial lockdown measures. How would these pressures reshape our social lives? Did the social distancing affect our fundamental social motives: the suites of cognitive, affective, and behavioral tools aimed at addressing the adaptive social challenges of protecting ourselves from dangerous others, avoiding contagious disease, finding and maintaining cooperative partners (affiliation), gaining and keeping status, finding mates, retaining those mates, and caring for kin? It did…and importantly did not.

To find this out, our international team of 66 researchers measured a total of 6,917 people’s fundamental social motives in 29 countries during the first year of the pandemic and compared this to data we had collected measuring 8,998 people’s motives in 32 countries before the pandemic began. We found that, as expected, people on average became more concerned about avoiding disease during the pandemic than before.

There were also several other smaller but sensible shifts in people’s motives. Unsurprisingly, we saw that people with children became even more concerned about caring for them during the pandemic: a strong drive to protect one’s offspring during a dangerous time. We may have also expected that the isolation—the inability to meet potential new romantic partners, spend time with friends, or interact with colleagues—would lead people’s mate seeking, affiliation, and status seeking motives to reactively increase and boost the pursuit of these goals. On the contrary, as people’s disease avoidance increased, several of the motives most likely to bring them near potentially contagious individuals—when finding mates, maintaining friendships, or gaining status—all decreased.

But in an important way, we saw no difference before versus during the COVID-19 pandemic. Before the pandemic began, we consistently saw across countries (and across several methodologies) that people were more motivated to care for their families and long-term romantic partners than to find new mates. And again during the pandemic, all around the world, people on average remained more motivated to care for family than to seek mates—and more motivated to care for family than to avoid disease!

Before the pandemic, people who were more concerned with caring for family also tended to be happier, with higher levels of well-being and lower levels of depression and anxiety, whereas people who were more concerned with finding mates tended be less happy, more depressed, and more anxious. On the other hand, both before and during the pandemic, people with higher disease avoidance motive tended to be less happy. Would the heightened disease avoidance concern during the pandemic smother a relationship between happiness and people’s kin care and mate seeking motives? Would happiness still be positively associated with family care for people confined to their homes, many now living in increased enforced daily contact with immediate family members? Yes, it seems that family still matters: During the pandemic, people who were more concerned with caring for family again tended to be happier, and those more concerned with finding mates again tended to be less happy.

Despite a large shift in disease avoidance motive, most of the other significant fundamental social motive shifts we saw during the pandemic were relatively small, and the overarching pattern of the preeminence of family-care motives remained. Yet as many people reinvented their daily lives, avoiding going in person to work, school, and even the grocery store, one could have expected to see even bigger shifts in their fundamental social motives. Why might that not have been the case? Perhaps the marvels of modern technology let many people remain connected enough to avoid the worst effects of isolation through video calls, social media, and even modern dating apps. Perhaps people’s fundamental social motives are resilient to certain shifts in external circumstances, temporarily spiking or dropping as a situation requires and then settling back to something like a baseline level. Or perhaps our samples did not include people who faced some of the worst effects of the pandemic. One thing that does seem clear, however, is that humans rely upon family to overcome many challenges, and even in the face of a global pandemic, family still matters most.

Read the paper: Family Still Matters, or read more about the published data which are freely available for use in your own work.

Pick, C., et al. (66 co-authors). (2022). Family still matters: human social motivation across 42 countries during a global pandemic. Evolution and Human Behavior, 43(6), 527-535.