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Humans are social animals, but sociality has both benefits and costs. On the one hand, other people provide safety in numbers, cooperation, care, love, and most of what makes a good life possible. On the other, they’re also potentially sources of infectious microbes. You can reduce your risk of catching something by avoiding close contact - but in doing so, you give up a lot. The question is, then: How do we decide whose germs are worth the risk?
One intriguing possibility is that we have an evolved tendency to risk exposure in proportion to people’s value to us as social partners - in other words, when the benefits are most likely to outweigh the costs. Earlier research offered some support for this idea, but it was unclear how widely it applied. If the tendency is part of human nature, we’d expect to see it across widely disparate societies. Do we, though?
In a new paper in Proceedings of the National Academy of Sciences (PNAS), an international team of researchers - led by Hongyu Sun and Josh Tybur and including yours truly - addressed this question with a sample of more than 40,000 people spread across 61 societies. Participants were randomly assigned to think about one of four categories of person: their closest friend, an acquaintance, a stranger, or someone they knew but intensely disliked. We measured how much each participant valued this person’s welfare through a series of choices between receiving money themselves vs. having the other person receive the money. Our assumption was that the more willing someone was to allocate money to another person, the more they valued them and the relationship.
We also asked participants how they felt about various kinds of potentially germ-sharing contact with the person. Would they be comfortable sitting close enough for their legs to touch, standing close enough that the person’s saliva could reach their face, or drinking from the same water bottle? Finally, we asked participants whether they’d touch the person during a typical greeting - for example, by shaking hands, hugging, or kissing.
As predicted, in all 61 societies, people were more willing to have infection-risky contact with people they valued more. As shown in the graph below, this was true both for everyday contact and for contact during greetings. Interestingly, the connection was stronger for the former than the latter. A plausible explanation is that greeting behavior is more strongly shaped by social conventions, and thus personal feelings have less room to influence our reactions in that context than they do for everyday contact. Note that it wasn’t just that people were more comfortable with friends than with strangers. Even within each relationship category, placing greater value on a person went hand in hand with greater willingness to have close contact with them.
Our 61 societies differed less than we expected in comfort with germ-sharing contact. Only about 3% of the variation in comfort with everyday contact was attributable to differences between societies. Physical contact during greetings varied somewhat more, with about 7% of the variation attributable to societal differences. Overall, differences within societies were much larger than differences between them.
Another issue we explored is whether people in societies with a greater historical prevalence of infectious disease were more wary of potentially infectious contact. Surprisingly, we found little evidence for a general link. Instead, the effect of historical disease prevalence depended on how much people valued the other person. For highly valued individuals, greater historical prevalence was associated with less willingness to have contact. For people who were valued less, in contrast, historical prevalence made little difference - perhaps because willingness to risk contact with such individuals is fairly low regardless.
There are limits to what we can conclude from our findings. Our study focused on people’s answers to hypothetical questions, which may or may not predict real-world behavior. Nor do our results prove that the relationship between interpersonal value and contact comfort is produced by a dedicated, evolved mechanism for pathogen avoidance. Other explanations are possible.
Still, our data are consistent with the idea that the more another person matters to us, the more germ risk we’re willing to accept for the sake of our relationship. The fact that this held across 61 societies, with little variation from one to the next, suggests that the tendency is part of human nature rather than purely a product of culture. Evolution has apparently been weighing the risks of a hug against its rewards for a long time.
You can access our paper here for free.
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Coming Soon to The Nature-Nurture-Nietzsche Newsletter…
The Dinosaurs That Evolved Primate-Level Intelligence - and Never Went Extinct
12 Things Everyone Should Know About Their Emotions
The Book Cordelia Fine Reviewed Isn’t the Book I Wrote (my response to Fine’s review of my book A Billion Years of Sex Differences)
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