Just as viruses, bacteria, and other pathogens are constantly evolving to invade our bodies, evade our immune systems, and make more copies of themselves that we then sneeze, cough, or otherwise disperse to infect others, our immune systems have been simultaneously evolving to fight back. This evolutionary arms race has been going on for hundreds of millions of years, but ever since the origins of agriculture, humans have made ourselves vastly more vulnerable to contagious diseases like cholera, smallpox, and RTIs that are passed from one person to another. Hunter-gatherers live in small
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