In the New World, on the other hand, no big-time diseases seem to have leapt from animals into the human population. While the Americas had cities as large as those in Europe, those cities were much newer at the time the Spanish arrived. People in the New World hadn’t been living in close quarters long enough for crowd diseases to spring up and propagate. Native Americans never had the opportunity to develop resistance to the myriad diseases that plagued Europeans. This genetic resistance, by the way, should not be confused with acquired immunity. Acquired immunity is when a body gets rid of a
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