"...Revenge may be frowned upon, viewed as morally destitute, papered over with platitudes about living well. But the urge to extract a pound of flesh, researchers find, is primed in the genes.
"Acts of personal vengeance reflect a biologically rooted sense of justice, they say, that functions in the brain something like appetite. Alternately voracious and manageable, it can inspire socially beneficial acts of retaliation and punishment as well as damaging ones. The emerging picture helps explain why many people who think they are above taking revenge find themselves doing nasty, despicable things, and how unconscious biases pervert what is at bottom a socially functional instinct."