Could the prevalence of disease really impact people’s behaviors so completely and consistently? With a new hammer, sometimes every shiny thing looks like a nail. Then swine flu H1N1 emerged. When swine flu came, some people started shaking hands less, wearing masks and, pity the thought, even kissing less—all because of the potential of catching one disease. Handshakes were skipped at college commencements. Mexicans were urged to not kiss on the cheek. Churches stopped having parishioners drink out of a common, holy cup. Suddenly the idea that diseases affect our behaviors seemed less remote.
So far, Fincher and Thornhill’s tests are really just correlations, the coincidence of certain aspects of culture and disease. Cultures are, for example, more diverse where there are more diseases—but many other factors are also different.
For example, all the places with lots of disease are also places favorable for growing many kinds of food. Perhaps being able to grow more kinds of food historically allowed more cultures to coexist, without competing, as has been argued by the anthropologist Daniel Nettle.
Some of the places with few diseases are also isolated. Perhaps, as Mike Gavin, at Victoria University in Wellington, New Zealand, has suggested, cultures that are more isolated are more likely to become different and a little wary of strangers.
But whether or not disease has caused the pattern of cultural variation, the scientists' analyses show that the patterns in human behaviors and culture are not random. Whether disease or some other factor is responsible, we have less control of who we are and how we behave than we might like to think. Our language, our sexuality—even how we tend to greet each other—are influenced by forces far from our daily control.
More research may tell whether Fincher and Thornhill’s models are general enough to be both useful and true. To date, Fincher told me, most of the e-mails he has received have been supportive. Some biologists have suggested the work is revolutionary. A few of the biologists who wrote to him were interested but cautious, and one or two disagreed with him completely. Somewhere, probably, a cultural anthropologist is writing and rewriting a thorough and vehement response.
In the meantime, we go on living our lives, imagining that we decide for ourselves who we are and how to act. But when the flu comes back this fall, watch your neighbors. Watch to see if their actions change. If Fincher and Thornhill are right, wherever the flu strikes, people will become more wary of strangers. Hands once extended freely will search for pockets. Where the disease is worst, the changes will be most rapid and extreme. Whole countries may even shutter their borders. Because while it is very hard to predict the evolution of H1N1 and the deaths it will cause, at least to Fincher the changes in our own actions may be more foreseeable. We are like small boats, pushed and pulled in the tides of disease.
Rob Dunn is a biologist at North Carolina State University and the author of "Every Living Thing: Man's Obsessive Quest to Catalog Life, from Nanobacteria to New Monkeys."