See my paper on the evolution of war Cain and Abel: Scarcity, Information and the Invention of WAR published in Cyberwar: Security, Strategy, and Conflict in the Information Age in support of Andrew Sullivan’s post on “Is War Innate?”

    The oldest evidence of deadly group violence by humans — a mass grave in the Nile Valley — is about 13,000 years old, and even that is an outlier. The vast bulk of evidence dates from 10,000 years ago or less, leading scholars such as Sarah Blaffer Hrdy, Doug Fry, Jonathan Haas and Erik Trinkhaus to conclude that war is a relatively recent cultural phenomenon, associated often … with agriculture and permanent settlements. … skeptics say, Well, we don’t have good evidence of any human behaviors more than 10,000 years ago. Actually, we have evidence of many complex cultural behaviors — tool-making, hunting, cooking, art, music, religion…far back in the Paleolithic era, but not war. The evidence is clear: war is a recent cultural phenomenon that culture can help us transcend.