ABSTRACT
Our germs, like our wheat and rice and goats and horses, are the creations, albeit unintentional in this case, of given societies at given times. As those societies grow and shrink in numbers, expand and contract geographically, shift from hunting and gathering to agriculture, flow into cities or desert them, travel on foot or by sailing vessel or jet planes, change diet, change sexual mores, have or cease to have contacts with various kinds of animals, and so on, they alter the environments of microorganisms and thereby change the characteristics of infections. These changes call for historical interpretation just as much as developments in politics, economics, or religions.
