The Black Death and AIDS: CCR5-Delta32 in genetics and history

Black Death and AIDS are global pandemics that have captured the popular imagination, both attracting extravagant hypotheses to account for their origins and geographical distributions. Medical scientists have recently attempted to connect these two great pandemics. Some argue that the Black Death of 1346-52 was responsible for a genetic shift that conferred a degree of resistance to HIV 1 infection, that this shift was almost unique to European descendents, and that it mirrors the intensity of Black Death mortality within Europe. Such a hypothesis is not supported by the historical evidence: the Black Death did not strike Europe alone but spread from the east, devastating regions such as China, North Africa, and the Middle East as much or even more than Europe. Further, in Europe its levels of mortality do not correspond with the geographic distribution of the proportion of descendents with this CCR5 gene. If anything, the gradient of Black Death mortality sloped in the opposite direction from that of present-day genotypes: the heaviest casualties were in the Mediterranean, the very regions whose descendents account for the lowest incidences of the HIV-1 resistant allele. We argue that closer collaboration between historians and scientists is needed to understand the selective pressures on genetic mutation, and the possible triggers for changes in genetic spatial frequencies over the past millennia. This requires care and respect for each other's methods of evaluating data.