Men may be 'natural avengers'.

Revenge may be far sweeter for men than it is for women, suggests a study released in January. When mate test subjects witnessed people they perceived as "bad guys" being zapped with a mild electrical shock, their M.R.I. scans lit up in primitive brain areas associated with reward, but their brains' empathy centers stayed dull Women watching the same punishment showed no pleasure response, but their brains' empathy centers glowed. Tania Singer, the lead researcher at University College London, says that the men "seemed to feet satisfaction when unfair people were given what they perceived as deserved physical punishment."