Group differences in proneness to inflammation.

All humans are primarily descendants from a diaspora out of Africa approximately 50,000 years ago although there are some indications of admixture with local populations of archaic humans outside Africa. The burden of infectious disease is greater in tropical Africa than elsewhere on earth in historic times, and it was less outside Africa, especially in the New World where passage through the Beringian filter kept many Old World parasites from entering the New World with humans. As a consequence we expect that the immune system, especially susceptibility to inflammation, will be "tuned up" in people with recent tropical African ancestry, intermediate in people of European and Asian ancestry, and perhaps "tuned down" in people of Native American ancestry. We suggest that evolved responses to different pathogen burdens among geographic groups may contribute to higher rates of inflammatory disease in modern people.