Around this time last year, as the COVID-19 pandemic gained steam around the world, the phrase “social distancing” quickly became part of popular discourse. But as a practice, social distancing has been around for a lot longer—and not just in humans.
A new review paper, out today in Science, combs the scientific literature to tease out some of the ways that disease outbreaks can shift social behavior, in both humans and in other animals.
“[Animals] have evolved really interesting, intricate behavioral strategies to deal with pathogens,” says lead author Sebastian Stockmaier, a PhD candidate in integrative biology at the University of Texas at Austin.
Stockmaier, who studies sickness behaviors in vampire bats, teamed up with a group of epidemiologists, evolutionary biologists, and other experts to write the review. Examining these social dynamics, the authors say, can help us understand incredibly important processes, like how diseases spread and how viruses evolve. And animal studies can help fill in pieces of the puzzle.
“The study of how contagious diseases spread is very complex,” wrote Patricia Lopes, an assistant professor at Chapman University who studies animal behavior, in an email to Popular Science. “What this review highlights is the multitude of ways in which the behavior of infected individuals or of healthy individuals surrounded by infected individuals can change, and how we find these changes in a wide range of animals.” Behavior, wrote Lopes, who was not involved in this review, “is a critical component in precisely determining or predicting how a disease will spread.”
Leaning in particular on research into the captivating lives of eusocial insects like ants and bees, the researchers looked at six different ways that the presence of contagious disease can change social interactions. Across taxa, pathogen avoidance is pretty common, Stockmaier says. That’s when you recognize that another individual might be sick, and keep your distance to avoid getting sick, too—like when someone sneezes near you at the cheese counter, and you instinctively back away. Lobsters practice pathogen avoidance, as do termites, and Trinidadian guppies.
“That’s a very beneficial behavior, when you can recognize infection in somebody else, and you can avoid becoming infected,” says Stockmaier.
The team also looked at a few different ways that individuals self-isolate—either inadvertently, because they’re feeling bad and can’t do everyday activities, or by actively isolating themselves to protect the group (ants and bees do this). And they looked at things like “exclusion”, where an infected or exposed human might be placed in quarantine—or, in the cutthroat case of honeybees, “dragged out of the nest,” Stockmaier explains.
In addition, the team reviewed behaviors like caretaking (mostly known in humans and social insects), as well as proactive social distancing, which many of us are now painfully familiar with—in other words, keeping away from each other even when healthy, in order to reduce the risk of transmission.
“Something very similar has recently been shown in these black garden ants that do something very intriguing,” Stockmaier notes. “If you introduce individuals that have these fungal spores on them, what will happen is that individuals inside the nest that are not infected will also step away from each other.”
For humans, the authors point out, these interactions can be especially nuanced. For example, a person who is feeling sick might still go to work if they’re laboring under a system that does not provide paid sick leave or incentivizes workers to prioritize productivity over health. These variables, the authors say, should be incorporated into future models.
The review, says Lopes, raises some exciting questions—for instance, “how can the pathogen try to manipulate our behavior to increase its own survival and reproduction?” Additional research examining “how the behavior of infected animals changes, how other animals detect sick animals, and what parts of these responses are driven by the pathogen versus driven by the infected individual,” she writes, “will increase our knowledge of how diseases move through populations and lead to improved public health policies.”
Overall, “I think it’s fascinating to look around in nature and see all these mechanisms that have become really relevant for us all of a sudden,” Stockmaier says. Unlike us, animals don’t have breaking news reports or social media to help guide their behaviors.
“How do those ants know how to step away from each other? It’s just fascinating that animals have evolved these strategies and use them, and that they’re very effective.”