Violence is a pervasive theme in human society; it fills our news broadcasts, our movies, our novels, and, most especially, our histories. Why are people (mostly men) so prone to murder? Many anthropologists and even philosophers like Jean-Jacques Rousseau have chiefly blamed the corruptions of living in mass society. Not so, argues a new study, “The phylogenetic roots of human lethal violence,” published in Nature by Spanish evolutionary biologists. They claim instead that natural selection has endowed us with our violent tendencies. The researchers’ strategy is to survey intra-species violence in over 1,000 mammalian species in an effort to trace how violence arose. They also look at databases that compile rates of violence among human hunter-gatherer bands and ancient civilizations. While we are not the most violent species (meerkats are), we are pretty high up there on the list.