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Do Wild Bats Hold the Key to Understanding Human Tribal Behavior?


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If you write a book and have some luck, people call to interview. Maybe not a lot of people, but a few. When I published my most recent book, my mom called, for example. Some radio stations did too, and then they asked questions. But, they never asked about the whole book. Some chapters never got mentioned. In my first book, interviewers never mentioned a chapter I wrote about the search for nanobacteria, not once 1. Late in my most recent book, The Wild Life of Our Bodies, I covered something even more radical—the possibility that infectious diseases make us tribal and prejudiced. No one ever asks about that chapter either2. I can’t help but wonder why. These two chapters are at the backs of their respective books. Maybe they are just beyond where a frantically reading reviewer or interviewer on a deadline dares go. But there is a more interesting possibility (at least to me); perhaps they deal with ideas too implausible to be worth mentioning on the air.

Glossing over the improbable chapters in books seems fair. Yet, the wonder of science is that sometimes implausible ideas are more than they seem. It was with a bit of delight that I read this morning that the hypothesis linking disease and tribalism–as bat shit crazy as it might be (note: I am using the term “bat shit” technically here, as will become clear)–had, indirectly, been tested.

Disease-causing pathogens–viruses, bacteria and protists–have geographies, both in terms of where they can be found and how common they are within those regions. The consequent map of malaise and death affects many aspects of the human story, including–Mark Schaller (son of George), Corey Fincher, Randy Thornhill (son of infamy) and others have argued–human behavior, culture, and politics. The most radical of these ideas suggest that where deadly, contagious, diseases are prevalent, humans tend to be xenophobic and cultures tend to be, well, tribal. Xenophobia is the fear of those who are different. Where it is strong, the odds of a disease passing from one group to another, might decrease, perhaps even enough to forestall the spread of epidemics. The concept is much the same as the one employed today at borders, where non-citizens are often regarded suspiciously, as potential bearers of the gift of pathogens.

Xenophobia and tribalism, once they emerge, can influence politics and nearly every other aspect of human civilization, particularly when acting in concert with deaths and malaise due to disease. High disease prevalence and xenopohbia has even been argued to have led to the diversification of cultures (if you don’t talk to your neighbor, it is easier to become different from them) and/or the rise and fall of empires.

Collectively, the ideas linking disease prevalence with human personalities and cultures are reaching and wild, the groping margins of science. But even if only partially right, they are important. Xenophobia and the tribalism it incites are at the root of wars. We fight, in part, because we believe each other to be different and alien, “xenos.” Tribalism is also at the root of how business leaders and department heads behave. Tribalism matters, as should its understanding, particularly if the factors that influence it are likely to change as we alter the world, as is surely the case for the prevalence of diseases. As climate changes, so too will change which diseases might be influencing who and how you are.

The original data in support of this suite of ideas come from psychology and biogeography. In psychological studies, individuals show strong, but subconscious, aversive, responses to features that seem to indicate illness (even if the person they are looking at is not actually ill). In biogeography, in those places where there is a greater prevalence of infectious disease, people do, on average, tend to be more xenophobic (based on standard psychological profiles done all around the world). This latter result is a simple correlation. It might be spurious. It might be due to other factors–climate, history, the fates–but, to my mind, it is at least intriguing enough to write about in the context of a whole book about how other species shape who and how we are, and so I did.

The trick with a feral ideas about culture is how to test them. If you have a crazy idea about how the human brain works, you can go poke a rat brain and test whether your idea is plausible. Progress in medical science builds one dissected rat at a time. If you have an idea about how human cultures work it is, well, harder to go poke a whole tribe (which hasn’t stopped anthropologists from, every so often across history, trying). But what you could do is poke at rat behavior, or better yet that of an animal that, like humans, sometimes assembles into large groups and, in other circumstances or species, eschews them. You could, in other words, go poke at the cultures of bunches of bats.

Recently, some scientists did just that, sort of. At the scale of North America we appear to have poked lots and lots of bats. More specifically, a new fungus has arrived in North America, most likely via introduction by humans, and it is killing bats. This fungus (Geomyces destructans) causes “white nose syndrome,” which was first seen in the U.S. in New York in 2006. Where it met the bats, the fungus spread quickly among roosts, killing nearly all of the little brown bats and other bat species in each of the caves in which it appeared. Bat bodies pile up in the guano at the bottoms of caves. The deaths are tragic and worst where bats are gathered most like humans, in dense aggregations, shoulder to tolerant shoulder. The situation is grim.

But not all is lost. Although it looked as though the little brown bats and several other species might soon face extinction, at least in some regions and perhaps even in North America, the little brown bats have begun to rebound in some places, albeit modestly. A new paper out this week takes notice of one of the reasons they appear to be rebounding, the bats are avoiding each other. Little brown bats (at least historically) tend to roost in large, groups, one next to the other, bumping fuzzies as it were. But not anymore. More and more, this new study, led by Kate Langwig, a graduate student at Boston University, suggests, the bats are spreading themselves out in their roosting caves, their hibernacula. Once, they clumped, warming themselves around the tiny fires of their bodies. Now, they go it alone.

Interestingly, this little brown bat behavior is precisely what the literature on human behavior, xenophobia and tribalism would have predicted. Langwig approached her study of the bats without a real hypothesis about how bat behavior might change after the disease swept through populations. In part, she and her colleagues simply didn’t anticipate that the bats would respond behaviorally at all, and yet, they seem to have.

Image: A pair of little brown bats, cuddling despite the consequences. Photo by Brandon Keim from Flickr creative commons.

Langwig’s results are preliminary, as she and her colleagues are the first to admit. She has measured the change in the bat roosting (and abundance) before and after the arrival of the disease, but she has not really studied the behavior of the bats and how it is they come to be spaced apart. Yet, the bats the are important from the perspective of the basic biology and conservation of the bats and so there remains much to do and much that can be done. For example, it would be good to know if the probability of transmission of the disease really goes down when the bats are further apart. It would also be interesting to figure out if the same individuals that were once nuzzling up next to each other are now hanging out on their own. Given how long bats can live, this seems likely, but it would be interesting to study in more detail. But the exciting thing, apart from the good news for the bats, is that the basic research being done on these bats is developing into a test of a theory that applies not just to the bats but also to you and me and the rest of humanity.

In part, for me personally, the challenge in believing that diseases might really affect human behavior, xenophobia and tribalism around the world is that for the most part this idea requires people to respond to diseases even if they do not understand their biology. It requires culture to evolve adaptively before understanding does. This is where the bats are especially interesting. Because if the bats really are changes their social behavior because of disease, they are not doing it because they understand the epidemiology of white nose syndrome. They are doing it because their behavior has been shaped in other ways. Perhaps the individuals who were least cuddly were the only ones who survived, which might either have favored cultural aspects of their behavior or specific genes.

The new bat study does not resolve anything conclusively with regard to the social behavior of bats OR humans, it is a hint of something interesting and general, but only a hint. The ideas remain speculative, if a bit more plausible than they seemed before. Yet, the bats suggests a path forward, a path we might proceed down if we want to get at the root of just why it is that human cultures vary so much from place to place in how they deal with others. None of us and none of our cultures are immune from tribalism, but just how much it rules our lives varies greatly. I will keep wondering why, wondering and keeping an eye on the studies of bats. The story of the fall and modest and antisocial rise of the little brown bats is another example of basic research3 that has the chance to tell us as much about who, as social mammals, we are as any study that we might consider to be more directly medical or otherwise applied. Sometimes we see more about ourselves by looking out to the wild species around us than we ever could by looking at ourselves 4.

Footnotes of article and marginalia of Rob’s brain.

1-With the exception of one conservative radio host who was glad to have an excuse both for his prejudice and his tribalism).

2-A search I thought, and think, is interesting as much for how similar it is to well-accepted stories of discovery as it is from a purely scientific point of view.

3-This particular study was funded by the National Science Foundation.

4-As for the nanobacteria, the possibility that they exist as self-replicating life-like, entities as fascinating as it is remote. Maybe some discovery will be revealed soon that sheds new light on the possibility and makes my chapter seem less crazy. On the other hand, there is always the other possibility. Perhaps what I wrote on nanobacteria was both crazy and, simultaneously, boring. If that is the case, maybe you can resolve the issue by reading the book. But, if you do, come to your decision privately, because while it may be the case that xenophobia in the general public can be caused by infectious diseases, it is definitely the case that xenophobia (and tribalism) in authors can be caused scathing reviews of book chapters.

Rob Dunn About the Author: Rob Dunn is a science writer and biologist in the Department of Biology at North Carolina State University. His first book, Every Living Thing, told the stories of the sometimes obsessive, occasionally mad, and always determined, biologists who have sought to discover the limits of the living world. His new book, The Wild Life of Our Bodies, explores how changes in our interactions with other species, be they the bacteria on our skin, forehead mites or tigers, have affected our health and well being. Rob lives in Raleigh, North Carolina with his wife, two children, and lots of microbes. Follow on Twitter @RobRDunn.

The views expressed are those of the author and are not necessarily those of Scientific American.






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  1. 1. tintin2sn 1:08 pm 07/12/2012

    I am not convinced that the bat example speaks to the effect of infectious diseases on tribalism in humans. There is an important functional difference between being less gregarious generally with others of one’s own species, and being less gregarious with conspecific outgroups. Because conspecifics share the same physiology, other individuals of one’s own species are more likely to act as vectors of disease transmission than are non-conspecifics. However, it is unclear that humans from different tribes are any more likely to be vectors of diseases to which one is vulnerable, compared to ingroup members from one’s own tribe. I think the bat analogy confuses this latter debate more than it clarifies it.

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  2. 2. crenshawseeds 3:47 pm 07/12/2012

    In A Tree Grows In Brooklyn, Francie Nolan’s mother puts kerosene in her plaits so other kids will stay away from her and she won’t get sick. It worked in the novel!

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