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.

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