Humans have been historically eager to kill each other. Throughout history, we've thought up all sorts of nutty reasons to slaughter our fellow man that had nothing to do with immediate survival of the fittest. We tend to chalk all these wars up to cultural differences fed by a species-wide need to be ideologically right (and impose that right-ness on others), along with a knack for weapons discovery culminating in a technology boom that's constantly supplying bigger and better ways to off each other. Add governments to the mix, and you've got a big steaming pile of questionably necessary interspecies violence. So it's a little—but not a lot—surprising that the growing scientific consensus is that war not only dates back to the origins of humankind, but has also played "an integral role" in or species' evolution. According to this theory, which emerged during a recent conference at the University of Oregon, the war "instinct" was present in our common ancestor with chimps, and has been a "significant selection pressure on the human species," as evolutionary psychologist Mark Van Vugt put it. His and his colleagues' reasoning goes something like this: Evidence exists to show that war and humans have been friends since the beginning (fossils of early humans show wounds consistent with combat injuries). As such, we would have evolved "psychological adaptations to a warlike lifestyle." To this end, researchers have presented "the strongest evidence yet that males—whose larger and more muscular bodies make them better suited for fighting—have evolved a tendency towards aggression outside the group but cooperation within it." In other words, men have evolved to be team players within their own clans, and be warriors with everyone else—much like the behavior observed in chimpanzees, who regularly engage in short bursts of intergroup violence to weaken neighboring groups of males. So should we resign ourselves to a future of ever-escalating violence due to our Darwinist predisposition for war? Not necessarily, says John Tooby, an evolutionary psychologist at the University of California at Santa Barbara, who insists on looking at the bright side:

"The interesting thing about war is we're focused on the harm it does... But it requires a super-high level of cooperation [within military organizations]."

Fair enough. Now if we could just figure out how to apply that trait to government. Related: RB: Over a Year After YouTube Ban, Military Launches “TroopTube” RB: How Green Is My Army?