Mark Schaller is a psychological scientist and Professor of Psychology at the University of British Columbia. He graduated from the University of North Carolina in 1984 and obtained a PhD in Psychology at Arizona State University in 1989. He's been at his current position at the University of British Columbia since 1996. Schaller's research looks into the cognitive processes that contribute to stereotypes and prejudices, as well as the implications of evolutionary fundamental human motives on social behavior, the psychology of kin recognition, and the psychological consequences of fame. The reason that he's important for our class at this very moment has to do with his research into and coining of the term "behavioral immune system."
So, to talk about the Behavioral Immune System, first we have to talk about the immune system. You know, that pesky little piece of your body that throws out fevers, sweating, swelling, et al. to deal with the stress you put your body through? Well, this system is actually very metabolically costly in its attempts to keep the body healthy. To mitigate the risk of these costs ever being incurred in the first place, human immune systems have also developed behavioral mechanisms that can prevent contact with foreign and harmful pathogens. We call this system of preventative behaviors the Behavioral immune system. Any time that you feel the need to stay away from people with known illness, you're experiencing the most obvious results of this system.
Other examples of this kind of proactive avoidant behavior can be seen in nature: Schaller lists tadpoles, mice, and chimpanzees as animals that are known to actively avoid other members of their species that are noticeably ill. The primary emotion that is associated with studies of this system is disgust, and Schaller seeks to examine how these feelings can effect social cognition and interaction within a given social ecology.
So, the Behavioral Immune system can be subdivided into two sorts of behaviors- detection and response. Detection primarily depends on smell and sight to find possible risks of infection around you. This includes both objects and behaviors of those around you who may be a vector of disease. The objects that subjects experience revulsion towards seem obvious-- fecal matter, vomit, etc. When it comes to how you react to those around you, however, that's where the research gets interesting. Test groups not only responded with avoidant behavior to those who were obviously sick or clearly unhygienic, but also to those who seemed visibly different from the cultural norm. The reasoning seems to be that those who are from outside of the local culture pose a threat not only because they may carry unusual pathogens, but also because they haven't been taught the local methods of hygiene. The findings don't stop there, however; there is also revulsion associated with those who are a part of the culture but differ from the "healthy" norm: the obese, the very old, the disabled. This can all be explained by the vast array of symptoms that may be signs of disease; the system over regulates because a false positive is less likely to cause harm than a false negative assumption of disease.
Interestingly enough, test groups didn't always experience these feelings of xenophobia or revulsion. Subjects who were more cognizant of the risks of disease were more likely to want to avoid outsiders and less likely to even be friendly within their own social groups. In one experiment, groups who were exposed to a video warning about the dangers of disease and foreign pathogens were much less likely to want to recruit workers from less well known or "unsafe" countries than those who watched a video about workplace accidents. In the real world, this translates into stronger feelings of xenophobia and fewer allowances for those who are "free thinkers" or otherwise non-normative in cultures which have historically higher rates of pathogen activity and greater diversity of pathogens, such as in equatorial regions.
This sort of predisposal towards those that the behavoiral system interprets as safe can also be seen in mate selection. Part of Schaller's findings showed predispositions towards less sexually promiscuous and more attractive partners that followed the same sort of increase in areas where pathogenic activity is high. This stems both from the increase in possible vectors of infection when partners are sexually active with multiple persons as well as the perceived genetic purity of those with symmetric faces.
Schaller concludes the article with a look into the portions of the system that are as yet not well understood. The Behavioral immune system does not exist in a vacuum, and many of the systems and behavioral cues that the system encourages also serve to help other, older systems. An easy target is the fact that the eyes and olfactory system obviously didn't evolve purely to spot pathogens. However, even disgust and revulsion, the primary forces of the system, were most likely coopted from the need to vomit and expel harmful substances once ingested. Additionally, though xenophobia, regulatory behavior within a social circle, and distrust of non-normative behavior are all tools of the system, there are other behaviors thought to play a role. People like doctors, soldiers, and youth and aged caretakers are all constantly participating in behaviors that increase the risk of pathogen infection, yet they enjoy positions of respect in most cultures. The sorts of assumptions of personal risk in exchange for lowered risk for the larger culture are still not very well explained by the Behavioral Immune System model.