This is startling:
[The paper] addresses the six-year disparity in life expectancy for blacks versus whites, arguing that much of the gap is due to a single factor: a higher rate of salt sensitivity among African-Americans, which leads to higher rates of cardiovascular disease, stroke and kidney disease.
Furthermore, it seems that the entire difference in salt sensitivity is the result of the transatlantic slave trade and the non-random sample of blacks that made it to America - non-random either because they were deliberately selected by the slave traders or because they were better able to survive the journey and resettlement.
The paper is here (free access), the excerpt is from a NYT profile of economics wunderkind Roland Fryer by Stephen Dubner. HT Tim Harford.