The Lost City of the Monkey God

by Douglas Preston

Alongside the domestication of animals, humans in the Old World began settling down in villages, towns, and cities. People lived together in much denser numbers than before. Cities, with their bustle, trade, filth, and close quarters, created a marvelous home for pathogens and an ideal staging ground for epidemics. So when diseases migrated from livestock to people, epidemics broke out. Those diseases found plenty of human fuel, racing from town to town and country to country and even crossing the oceans on board ships. Biologists call these “crowd diseases” because that’s exactly what they need to propagate and evolve. Epidemics periodically swept through European settlements, killing the susceptible and sparing the robust, culling the gene pool. As always, children were the majority of the victims. Almost no disease is 100 percent fatal: Some victims always survive. The survivors tended to have genes that helped them resist the disease a little better, and they passed that resistance on to their children. Over thousands of years and countless deaths, people in the Old World gradually built up a genetic resistance to many brutal epidemic diseases.