Despite our well-attested distaste for pseudo-scientific historic theories, for once I must come to the defense of the usually very fatuous Mr. Diamond, at least when it comes to his claim that civilization reduces violence. Conflicting claims of clashing anthropologists notwithstanding, there is little doubt that men pursue violence against one another at the slightest provocation and that in the absence of the apparatus of civilization in the form of law and its enforcement, such violence tends to only escalate.
The fact is that there are no paleolithic tribal societies still in existence that remain untouched by contact with our civilization, and — even if there were, in an ironic parallel to quantum theory — we could not study them without changing what we see. It is thus an exercise of most utter of futilities to claim, based on very spotty, often over-interpreted and — to begin with — circumstantial evidence that the original human social structures were free of war-making. Perhaps we could ask their contemporaries, the Neanderthals, for some corroboration?