Germs on the Brain

Psychologists theorize that our innate “behavioral immune system” programs us to irrationally shun strangers out of a subconscious fear of disease.

The long battle between humans and infectious microbes has left its marks all over us. It shows up most obviously in the way our bodies are constructed. The thousands of species of bacteria that swarm over us cannot penetrate our multilayered skin. Entry points, such as the eyes and the nose, are bathed in moisture to help flush out pathogens. The lining of our lungs releases bacteria-killing compounds. Viruses that manage to infect cells are greeted by proteins that attempt to shred them into g...

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