Robin was one of the people initially impressed with Ryan & Jetha, later persuaded by Saxon in "Dusk".

I personally recommend Azar Gat's "War in Human Civilization" as much more sweeping than Keeley's book. Despite the title, it's range precedes civilization, and even the emergence of humanity (although those are smaller portions of the book near the beginning). My posts about it are here. At any rate, there seems to be substantial evidence for warfare (or at least something analogous to "gang war" given their social scale) among hunter-gatherers, even if not to the extent of primitive agriculturalists like the Yanomamo or New Guineans.