The role of bacteria and viruses in world history

The Economist:

According to Jonathan Kennedy, the author of “Pathogenesis”, there is a better explanation for why H. sapiens prevailed: their immune systems were superior. As their populations boomed, genetic diversity increased and, since they lived in Africa, much closer to the equator than other humans, H. sapiens would have been exposed to a greater array of animals carrying a variety of microbes. Some of those microbes would have been pathogenic. (Indeed, the majority of bugs that infect humans are zoonotic—ie, they jump the species barrier from other animals.)

As H. sapiens moved across the world, they would have been protected against the diseases carried by the other humans they met. The converse was not true, however, meaning Neanderthals and other humans were less resistant to the diseases carried by H. sapiens.