Major Histocompatibility Complex in Humans: The Implications

Native Americans were wiped out by European diseases due to a very narrow MHC differential. Africans, by contrast, had a very wide spread in their populations' MHC and they were almost unaffected by the same European diseases. The MHC is a major genetic instruction set for immune systems.

The narrow scope of MHC types in Native Americans is due to genetic bottle-necking that occurred as groups of people crossed the land-bridge connecting Asia to the Americas. From mitochondrial DNA sequencing we can conclude that as few as 80 individuals survived that crossing. Only 80 people populated the whole of the Americas.

That small breeding population is the reason Native Americans were not equipped to immunologically defend against the introduced infectious disease. The MHC is differentiated in populations by genetic diversity which these new arrivals did not posses.

An experiment was run where female college students smelled T-shirts worn for 2 days by male college students (no soaps, deodorants, or cologne). Most of the women preferred the scent of the males that possessed different MHCs than their own. In a bizarre turn of events, women on contraceptives preferred the scent of males with similar MHCs.