According to evolutionary psychologists, humans don’t just have a physiological immune system, but an emotionally-driven, behavioural immune system too. The behavioural immune system makes us develop unconscious biases and habits to prevent us from encountering things that could potentially harm us. Think about your own behaviour during the Covid-19 pandemic -- you might have found yourself steering clear of people not wearing masks, or even holding your breath when passing close by someone. You’ve maybe even done this without thinking about it! According to a great number of evolutionary psychologists, this kind of behaviour is our nervous system’s way of preventing the side effects of a physiological immune response such as a fever or a cough. After all, the best way to win a fight is to avoid it in the first place!
One simple way the behavioural immune system works is how we often feel disgust or substantial aversion to things that could make us ill. It could be rotting food, a rat, or a spider -- animals that have been known to spread disease at times. This “pathogenic disgust” can also make us feel aversion towards fellow humans who don’t follow normal societal hygiene practices. One fascinating study showed that people who simply saw someone sneezing had almost immediate increases in their white blood cell production -- the cells that fight off illness.
But the behavioural immune system’s work isn’t always good, it should be said. While it’s there to protect us, it does not operate on a higher-level thought process. This means that it can be quite unsophisticated, and lead to issues like social anxiety, or even problematic biases like xenophobia or unhealthy cultural stereotypes.
