Want to fight prejudice? Just wash your hands.

Evolutionary psychology has a lot of ideas that are, well, pretty nutty. The latest theory argues that social prejudice can be fought by being more careful about the spread of disease. It's definitely nutty...but it might also do some good.

The underlying theory is that ancient humans once had to be extremely wary of strangers who might carry disease. While more welcoming groups might occasionally catch a deadly plague and die out, the more distrustful groups were much more likely to survive any outbreak, and so social prejudice against those who are different essentially evolved as a sort of population-wide immune system.

To be fair, this isn't the most ridiculous argument I've heard from evolutionary psychology (though that's not saying much). But it is the sort of thing that you kind of have to take on faith at this point - there really isn't any way to back it up with direct evidence, and there are plenty of alternative ways to explain the same basic behaviors.

Still, new research by the University of Toronto's Julie Y. Huang, Harvard's Alexandra Sedlovskaya, MIT's Joshua M. Ackerman, and Yale's John A. Bargh does offer some rather intriguing potential support for the idea that fear of disease and prejudice are linked. They found that public health measures ranging from extremes all the way down to simple hand washing made people feel more secure, and they in turn showed reduced bias against "out" groups, which included such diverse groups as immigrants, crack addicts, and the obese.

The team ran a series of experiments. In the first, 135 subjects were divided into two groups, one of whom had already received a flu vaccine while the others had not. They were then randomly divided again so that half the people from both groups read a passage on the dangers of flu. In the second experiment, 26 people, all of whom had been vaccinated, were given two different sets of texts to read, one that promised the vaccine was effective, while the other simply explained how the vaccine worked.

The test subjects were all then given questionnaires to fill out about how biased they felt towards different groups. In the first experiment, among those who had read the passage about the disease threat, those who were vaccinated were consistently less biased towards others than those who had not been vaccinated. There wasn't a significant difference in bias among those who hadn't read the passage at all. In the second experiment, those who had been assured the vaccine was effective showed less bias.

Finally, a third experiment had 26 undergraduate subjects, in which half used hand-wipes to clean their hands and a keyboard they were using, while the other half did nothing. Both groups then read a text that included the information that hand-wipes help stop the spread of disease. The researchers then asked the subjects questions to determine their feelings about germs, seven out-groups, and two in-groups (their fellow undergraduates and their families). Those who had not wiped their hands showed significant, correlated aversion to both germs and the out-groups, while nobody displayed prejudice against those like themselves or their families.

The results here are interesting, even if the number of experimental subjects sounds a bit low. The researchers conclude that the best way to fight the ancient roots of prejudice is to make public health a priority, stressing vaccinations and washing of hands. While I'm still more than a little skeptical that the solution is really that simple, I'll say this much - even if this plan doesn't solve all human prejudice, at least we'll all end up way healthier than we were before. That's the sort of evolutionary psychology I can get behind.

Via the Association for Psychological Science. Image by aka NickNguyen on Flickr.