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“The pandemic exposes human nature: 10 evolutionary insights

Benjamin M. Seitz, Athena Aktipis, David M. Buss, Joe Alcock, Paul Bloom, Michele Gelfand, Sam Harris, Debra Lieberman, Barbara N. Horowitz, Steven Pinker, David Sloan Wilson, Martie G. Haselton

Proceedings of the National Academy of Sciences, Oct 2020

PNAS first published October 22, 2020

Edited by Michael S. Gazzaniga, University of California, Santa Barbara, CA, and approved September 16, 2020 (received for review June 9, 2020)

https://doi.org/10.1073/pnas.2009787117

Abstract

Humans and viruses have been coevolving for millennia. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, the virus that causes COVID-19) has been particularly successful in evading our evolved defenses. The outcome has been tragic—across the globe, millions have been sickened and hundreds of thousands have died. Moreover, the quarantine has radically changed the structure of our lives, with devastating social and economic consequences that are likely to unfold for years. An evolutionary perspective can help us understand the progression and consequences of the pandemic. Here, a diverse group of scientists, with expertise from evolutionary medicine to cultural evolution, provide insights about the pandemic and its aftermath. At the most granular level, we consider how viruses might affect social behavior, and how quarantine, ironically, could make us susceptible to other maladies, due to a lack of microbial exposure. At the psychological level, we describe the ways in which the pandemic can affect mating behavior, cooperation (or the lack thereof), and gender norms, and how we can use disgust to better activate native “behavioral immunity” to combat disease spread. At the cultural level, we describe shifting cultural norms and how we might harness them to better combat disease and the negative social consequences of the pandemic. These insights can be used to craft solutions to problems produced by the pandemic and to lay the groundwork for a scientific agenda to capture and understand what has become, in effect, a worldwide social experiment.

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“Nothing in biology makes sense except in the light of evolution” (1), and nothing about the human response to COVID-19 will either.

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Insight 1: The Virus Might Alter Host Sociability

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There are two possibilities for how SARS-CoV-2 might be altering human behavior. First, it may be suppressing feelings of sickness during times of peak transmissibility. SARS-CoV-2 is characterized by a high rate of viral shedding, and the peak of viral shedding—and therefore transmissibility—occurs 1 d to 2 d before the onset of symptoms (5). It is possible that SARS-CoV-2 has been particularly successful because it is highly infectious before symptoms appear. Suppressing sickness-related behavior of hosts is one way that viruses can increase their fitness. Hosts that are infected but do not feel sick are more likely to go about their usual activities, which allows them to come in contact with others whom they might infect. If they do not display symptoms of infection, the human behavioral immune system fails to activate in others (see Insight 3: Activating Disgust Can Help Combat Disease Spread), silently spreading to new hosts.

The second possibility of how SARS-CoV-2 could affect host behavior is by contributing to mood disorders, such as mania, that could increase activity levels and decrease feelings of sickness, at least temporarily, during times of peak transmissibility. This could potentially lead to a “tug-of-war” over host behavior, with the virus “pulling for” greater host activity and sociability and the host fighting against this to reduce activity and instead prioritize healing. If sometimes the virus is winning and other times the host immune system is able to regain control, this could manifest as a mood disorder with periods of high activity/sociability and depression/fatigue, respectively.

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Similarly, if SARS-CoV-2 is affecting host social behavior, this would also affect epidemiological models, because contact rates change over the course of disease progression (10).

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Insight 2: “Generation Quarantine” May Lack Critical Microbial Exposures

The pandemic has focused the world’s attention on microbial influences on human life. Whereas the emphasis has been on the SARS-CoV-2 virus, quarantine has temporarily halted the regular exposure to novel pathogens that is characteristic of human social interaction. An evolutionary perspective reminds us we must consider the potential trade-offs of this intervention. Children and adolescents whose immune systems and brains are actively shaped by microbial exposures may be most impacted by this change.

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Although reduced exposure to neuropathic viruses during quarantine may protect some, normal brain development requires adequate and diverse microbial exposure. During development, communication between the gut microbiota of a young animal and the microglial brain cells that shape networks through myelinization and selective synaptic pruning influence its future cognitive, motor, and affective characteristics (17).

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But the risk-taking, neophilia, and drive to be sexual and socialize that characterize adolescence and promote dispersal are influenced by microbiota now fundamentally altered for many millions of adolescents around the world. COVID-19 has temporarily ended practice dispersals, physical peer-to-peer play, sexual activity, and other activities which would otherwise bring millions of adolescents into contact with novel microbes.

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Insight 3: Activating Disgust Can Help Combat Disease Spread

Disgust is a physical and social protective system that is a product of, and sheds light on, our evolutionary past. Disgust protects across three domains, all of which relate to pathogen exposure (25, 26). First, disgust is part of our food psychology and motivates avoidance of foods harboring, for instance, signs of toxins and microorganisms. Second, disgust is part of our sexual psychology and motivates avoidance of sexual partners (e.g., family members) judged to potentially risk the immunocompetence and, hence, health and viability of offspring. Last, and most pertinent, disgust is part of our physical contact psychology and motivates avoidance of individuals displaying signs of infection, surfaces revealing microbial infestation, and the skin, mouth, anus, and bodily fluids of unknown others. Together, consumption, coitus, and contact are all behaviors regulated by disgust and—because of the link to disease—all associated with one or more historical foodborne, sexually transmitted, or contact-facilitated pandemics.

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Disgust might therefore be important, although sometimes less potent than other emotions, such as empathy, to persuade people to distance.

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Insight 4: The Mating Landscape Is Changing, and There Will Be Economic Consequences from a Decrease in Birth Rates

Differential reproduction is the key to change over time. Humans have an evolved menu of mating strategies as products of successful reproduction, including long-term pair bonds, short-term casual sex, and everything in between (29). The COVID-19 pandemic is influencing these mating strategies and will have a profound impact on the global mating and economic landscape.

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Short-term mating is the most obvious strategy to be affected. Novel sex partners are potential virus vectors, rendering the costs of casual sex steeper. In-person sex is being replaced, perhaps temporarily, with online versions—sexting, video cams, and virtual sex.

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An evolutionary perspective predicts that those who pursue a fast life history strategy—marked by short-term mating pursuit, frequent partner switching, deceptive mating tactics, and steep future discounting (30)—are most likely to risk in-person sex during the pandemic and become potential superspreaders.

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Touch and scent are central to mating compatibility (31), but distance deprives individuals of this vital information. Mating at a distance exacerbates the tendency of people to interpolate positive values for qualities for which they lack reliable information, such as honesty, emotional stability, and sexual history. This overidealization creates unrealistic expectations that risk being shattered when an eventual meeting takes place in real life.

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An evolutionary perspective predicts that women will be reluctant to commit to men lacking financial stability, given the priority they place on this quality in long-term mating (32). It also predicts that men, in turn, will postpone marriage until they feel they have adequate resources to attract women of adequate or commensurate mate value (33). As marriage rates plummet and people postpone reproduction, at least for a period of time (34), some nations already on the cusp of population replacement level will fall dangerously below it as people opt to avoid bringing a baby into a virus-plagued world. Birth-rate drops, in turn, have cascading consequences for economic outcomes—job opportunities, the ability of countries to provide safety nets to an aging demographic, and a global economic contraction.

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Insight 5: Gender Norms Are Backsliding, and Gender Inequality Is Increasing

With schools shut down, families have unanticipated needs for childcare. Who is picking up this slack? In April of 2020, women lost more jobs than men, in part because more women than men are employed in hospitality and service industries that lost customers. However, at that same time, women more than men felt more pressured to quit their jobs in order to manage added household responsibilities of childcare and education, and worried more that declines in their productivity during the pandemic would negatively impact their careers (35). Before the pandemic, women already felt more stressed than men by competing family and job roles (36). With children at home, that stress seems to lead women to become homemakers and makeshift teachers.

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The default explanation in social science is to blame outdated gender stereotypes and lack of empowerment for women (39). However, women’s and men’s evolved preferences play an important role. One of the insights from evolutionary approaches to understanding sex differences is that women are far more limited in the number of offspring they can produce in their lifetimes than are men (40), and women, like females across primate species, have evolved to contribute a higher level of obligatory investment in each offspring through pregnancy and lactation (41). Therefore, throughout evolutionary history, a woman’s reproductive fitness hinged on the success of each individual offspring to a greater extent than a man’s. As a result (or in concert), women evolved stronger motivations to attend to the details of childcare and may feel pressured to accept more childcare and homemaking responsibility when others, such as teachers and childcare workers—or extended kin, who might otherwise help out—cannot.

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For instance, in cities and nations with greater economic inequality, women self-sexualize more in social media posts (45). For men, economic inequality at both the cross-cultural level and neighborhood level is associated with increased rates of male-on-male homicide, which seems to be driven by men’s concerns with social status rather than a purely instrumental need to survive (46).

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Insight 6: An Increase in Empathy and Compassion Is Not Guaranteed

There is anecdotal evidence that, in previous crises, such as hurricanes, earthquakes, and terrorist attacks, the common reaction—contrary to popular belief—is not a descent into savagery. Rather, in cases such as Hurricane Katrina and the London Blitz, there is an outpouring of solidarity and mutual aid (48). Barriers of class and race are temporarily suspended, and the benefit of the collective becomes priority (49).

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This is all consistent with a Rousseauian perspective: Human nature is fundamentally kind, and, stripped of the constraints of civilization, we are more equal, more generous, and mentally healthier. But there are also reasons to favor a less rosy view. Research on the behavioral immune system suggests that disease threat makes people intolerant and punitive toward outgroups (54). Nations with a history of high levels of infectious disease have lower rates of extraversion (55), and experimentally inducing disease threat spurs social withdrawal (56).

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Furthermore, at least in the United States—although less so in countries such as Canada—this pandemic is not bringing people together; rather, responses reflect the partisan divide that so characterizes recent times, with conservatives and liberals having different views about wearing masks, the wisdom of a continuing lockdown, and much else.

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Insight 7: We Have Not Evolved to Seek the Truth

Humans evolved in small groups under threat of starvation, predation, and exploitation by outsiders—and generally lived brief lives, favoring short-term strategies for consuming resources that could support successful reproduction (59). We have not evolved to think clearly about long-term threats like pandemics—which are statistically abstract and global. And yet, for at least a century, we’ve understood that the threat of a deadly pandemic is real and ever present (60). How should we have responded to this knowledge?

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Unfortunately, most of us are terrible at weighing risks presented as abstract probabilities (61). We also heavily discount the well-being of our future selves (62), along with that of distant strangers (63) and future generations (64), and in ways that are both psychologically strange and, in a modern environment, ethically indefensible. We’re highly susceptible to conspiracy thinking (65), and display an impressive capacity to deceive ourselves, before doing the hard work of deceiving others (66). These predispositions likely endowed our ancestors with advantages (67, 68), but they also suggest that our species is not wired for seeking a precise understanding of the world as it actually is.

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When we encounter friends or family in thrall to some fresh piece of misinformation, we often lack the courage to correct them. Meanwhile, behind a screen of anonymity, we eagerly confront the views of complete strangers online. Paradoxically, the former circumstance presents an opportunity to actually change opinion, while the latter is more likely to further entrench people in their misinformed views (70).

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Insight 8: Combating the Pandemic Requires Its Own Evolutionary Process

Some of the insights above point to flaws in our human nature that contributed to the pandemic and may make navigating it more difficult. But humans are paradoxical creatures. On one hand, we are products of genetic evolution in ancestral environments that bear little resemblance to modern environments. These “evolutionary mismatches” are likely responsible for our frequent lack of alarm in response to the pandemic. On the other hand, we constructed those modern environments, so our capacity for rapid cultural evolution—via behaviors, values, and technologies—must be acknowledged along with our genetic human natures.

This duality is captured by the label dual inheritance theory, which posits both a genetic stream and a cultural stream of inheritance that have been coevolving with each other for as long as we have been a species (71). The slower process of genetic evolution often follows where the faster process of cultural evolution leads, as we know from classic examples such as lactose tolerance in adults (a genetic adaptation) in cultures that keep livestock (a cultural adaptation) (72).

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Insight 9: Cultural Evolutionary Forces Impact COVID-19 Severity

Evolutionary principles can be applied to understand cultural adaptations during the COVID-19 pandemic. Human groups under collective threat experience evolutionary pressures to tighten social norms and punish people who deviate from norms. Accordingly, we can predict that societies worldwide will tighten in response to the pandemic. From an evolutionary perspective, strict norms and punishments that deter free riders are essential to helping groups coordinate their social action to survive, and thus would be adaptive in times of threat. Consistent with this reasoning, nations with histories of ecological and human-made threats (e.g., natural disasters, disease prevalence, resource scarcity, and invasions) tend to be tight (i.e., have stricter norms and little tolerance for deviance), whereas groups with less threat tend to be loose (i.e., have weaker norms and more permissiveness) (76). Variation in tightness in nonindustrial societies is also related to collective threats such as pathogen prevalence, population pressure, scarcity, and warfare (77).

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Accordingly, groups require stronger norms and punishment of deviance to survive under high threat (78). Indeed, experimentally priming humans with collective threat leads to an increase in desired tightness—either from God or government (79, 80).

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The varying reactions of nations around the world to early stages of the pandemic reveal potential evolutionary mismatches, wherein some loose societies have had a delayed and often conflicted reaction to tightening norms. Countries that are tight (e.g., South Korea, Japan, China) have been highly effective at limiting COVID-19 cases and deaths (81). By contrast, loose cultures (e.g., Spain, Brazil, and the United States) have had an explosion of cases and deaths in early stages. EGT models also illustrate that loose cultures take far longer to cooperate when under threat than tight cultures (82). Because people in loose cultures have generally experienced fewer ecological threats, they may be more likely to underestimate the risk of COVID-19 than those in tight cultures.

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Insight 10: Human Progress Continues

Evolutionary reasoning makes several predictions about the future humans will face in the wake of the pandemic––from shifts away from economic independence for women to birth rates dipping below thresholds needed to maintain some human populations. These are some depressing possibilities that invite a conclusion that humanity is spiraling downward to a new low point. Those who deny the possibility of social progress might feel vindicated by the COVID-19 pandemic of 2020, because it shows that life has gotten worse rather than better. But has it?

Many people have trouble reconciling the demonstrable fact of human progress—that, over time, we have become healthier, better fed, richer, safer, and better educated—with the constraints of human biology. Some fear that, if the mind has evolved as a complex structure, then progress would be impossible, because “you can’t change human nature.” Therefore, either there cannot be such a thing as progress or there cannot be such a thing as human nature.

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Conclusion

COVID-19 has brought radical change, through deaths, stress of extended quarantine, confusion that slowed adequate responding, social unrest at a massive scale, and a long and uncertain social and economic aftermath. This radical change is global—no human, anywhere, is unaffected by COVID-19.

To understand the virus and our response to it, we need to understand how viruses and humans evolve. We know that there is a long history of the coevolution of viruses and humans. Viruses evolve to exploit their hosts to encourage their own replication, but they also depend on hosts to survive. Humans can tolerate some manipulation by viruses, but we have also evolved to combat them. This delicate coevolutionary dance is why we often seem to be running as fast as we can, just to stay in the same place (90).

However, humans also possess the tool of scientific insight that gives us a broader view than what the virus can see. Perhaps this can help us stay one step ahead. By understanding the nature of viral strategies, we can better anticipate the spread of COVID-19 and try to block it. Likewise, by understanding human nature, we can try to activate evolved motivational systems that will help fight the virus, such as providing cues that trigger our behavioral immune system. Understanding human nature will also enhance our ability to address the aftermath of COVID-19, as it has disrupted so many of our fundamental human activities, such as mating, parenting, and simply maintaining social contact.

Herein, we have described 10 insights offered by a broad range of evolutionary thinkers, with expertise ranging from evolutionary medicine to broadscale cultural evolution. These insights offer possibilities for guiding science to address the spread of COVID-19 and its inevitable aftermath. However, these insights represent only a limited snapshot of this historic moment, and a selection of topics, although important, that an evolutionary perspective on the pandemic can provide.

The objective in providing these insights is to help make sense of the vast confusion that mars this pandemic and to illuminate paths for research. In addition to insights that can produce immediate action, the pandemic has provided us with unique opportunities to witness human nature as it unfolds, from changes in patterns of reproduction, shifting social norms, and curiosities of cognition that can warp our recognition of threat. This paper is a call to action in science—both in the application of existing knowledge about viral and human nature and also as an opportunity to make discoveries that would not be possible except when a global social experiment is underway.”