For decades, scholars have sought to answer this bloody question: Why has the murder rate been disproportionally high in the South for more than a century? Some argue it's the weather -- hot, steamy conditions setting tempers on edge and provoking deadly violence. Others blame widespread poverty and illiteracy. Still others fault a so-called southern "code of honor" that requires any slight to be avenged.

Now three sociologists have found an additional explanation: lynchings.

Steven F. Messner of the State University of New York at Albany and his collaborators Messner and his colleagues produced two maps. One showed homicides: Those counties with the highest rates were colored black; those with lower rates were shaded gray, while those with the lowest rates were white. The second displayed lynchings, using the same shadings. Counties with the most lynchings were colored black, those with a lower rate were gray and those with the lowest rates were white.

A quick glace at the maps revealed a chilling pattern. The dark areas roughly overlapped: the counties with the most lynchings had the highest homicide rates, while counties with fewer lynchings had comparatively fewer murders.