A rare medical condition may be partly to blame for the violent feud between the Hatfields and the McCoys.
The feud is the most-celebrated rivalry between two families. Between the years 1863 and 1891 violence between the two families resulted in at least a dozen deaths and many judicial proceedings, including a ruling by the US Supreme Court.
In a 2007 study, a team of doctors and geneticists who had studied dozens of McCoy descendants noted an unusually high rate of Von Hippel-Lindau disease. This rare, genetic condition triggers an increase in the “fight or flight” hormones, resulting in marked increase in aggressive tendencies. Researchers speculate that the disease may be partly responsible for the longevity of the feud and its persistent escalations.