Mark Schaller, a University of British Columbia psychology professor who has studied the behavioral immune system, explained that yes, the effect sizes are often small, but that in psychology, “even small effects can have big consequences.” The behavioral immune system is one reason why xenophobic attitudes exist, he argues, but that doesn’t mean it’s the only one. The Nazis compared the Jews to rats, which are associated with infectious diseases, but they also claimed Jews were hurting the economy, which has nothing to do with disease or disgust. And while it’s true that people have not always approached avoiding disease logically or rationally, that’s just the point, Schaller says. The behavioral immune system isn’t rational. It’s reflexive, and it’s willing to endure a thousand false alarms for every real threat.

Some researchers I spoke with are beginning to make connections between the behavioral immune system and our actual, biological immune system. People who carry a particular variation of the ACP1 gene are more susceptible to parasitic and infectious diseases, and, Murray and his colleagues found, they also happen to be less extroverted.174 In other words, they avoid going out and meeting new and different people, who might be carriers of unfamiliar pathogens. If you are the kind of person who gets sick easily, your body might just nudge you to get out less and expose yourself to fewer new people.

The emerging picture from these studies suggests the two immune systems work in concert, alternately kicking in and backing down as they’re needed. People who are more careful about germs—who, say, open the bathroom door with a paper towel—have less inflammation, which is the way our body typically protects us from pathogens.175 When you’re taking pains to avoid germs—when your behavioral immune system is revved up—your body realizes there’s less of a need for it to fight infections below the skin, so it turns down the inflammatory activity.

For some of the nonconformists I interviewed, there was a noticeable pattern of being avoided—almost literally—like the plague. Their ideas seemed to, frankly, gross out their neighbors. These days, “catching the gay” is an outdated joke about bigots, but for some outcasts, it still feels as though their peers fear being infected with their ideas. They spend their lives being kept at a distance by others’ behavioral immune systems. Next, we’ll learn just how damaging this kind of alienation can be.

Chapter 4

The Sting