Rutgers professor Brain Ferguson is one of the leading anthropologists of war and in the Bloggingheads.tv interview embedded below (or click here) he argues the evolutionary state of nature was not Hobbesian (i.e. warlike), but broadly Rousseauian (i.e. peaceful). To be clear, Ferguson does not deny that warfare exists worldwide, his position is that it emerged in the Mesolithic and that the Paleolithic - the period during which humans evolved - was therefore largely peaceful. Ferguson discusses, among other things, Lawrence Keeley's War Before Civilization (which I reviewed here), Azar Gat's War in Human Civilization (which I read recently and will hopefully review soon), Wrangham & Peterson's Demonic Males and Napoleon Chagnon's influential Science paper "Life Histories, Blood Revenge and Warfare in a Tribal Population".
While I don't agree with Ferguson's conclusion, the interview is highly recommended if you are at all interested in prehistory or human evolution.