The end of the Ice Age changed the meaning of geography. The poles remained cold and the equator remained hot, of course, but in half a dozen places between these extremes—what, in Chapter 2, I will call the original cores—warmer weather combined with local geography to favor the evolution of plants and/or animals that humans could domesticate (that is, genetically modify to make them more useful, eventually reaching the point that the genetically modified organisms could survive only in symbiosis with humans). Domesticated plants and animals meant more food, which meant more people,
