Slavery created a selection pressure that favored for survival those individuals who retained water in their blood, since dehydration from hard labor under the sun worsened fever mortality.  Somewhere in the genetic map of African Americans is genetic recombination which once offered that advantage, and now accounts in part for the higher incidence of African-American hypertension.  This is one of many mysteries that may be revealed now that geneticists at Harvard and Oxford Universities have constructed the world’s most detailed genetic map-of African Americans-based on 30,000 individuals.  MORE