Collision Detection said:
Evolutionary theory has long been puzzled by left-handedness. Southpaws are in the minority, and they get into many more accidents than do the right-handed; in the modern context, this is partly because so many quasi-lethal tools are engineered primarily for right-handed use. So the question is, given that left-handedness is so dangerous to one's health, why haven't southpaws evolutionarily vanished?
Possibly because southpaws are extremely good at one thing: Killin' people.
The Economist adds:
While there is no suggestion that left-handed people are more violent than the right-handed, it looks as though they are more successfully violent.
Natural born killers [Collision Detection, Dec. 26, 2004]
Handedness, homicide and negative frequency-dependent selection [Charlotte Faurie and Michel Raymond, Proceedings of the Royal Society]
A sinister advantage [The Economist, Dec. 9, 2005]