The existence of war in humanity’s hypothetical state of nature has been a controversial topic in the history of ideas. According to American cultural anthropologist and ethnographer Raymond C. Kelly, the earliest hunter-gatherer societies of Homo erectus population density was probably low enough to avoid armed conflict. The development of the throwing-spear, together with ambush hunting techniques, made potential violence between hunting parties very costly, dictating cooperation and maintenance of low population densities to prevent competition for resources. Raymond believes that this period of “Paleolithic warlessness” persisted until well after the appearance of Homo sapiens some 315,000 years ago, ending only at the occurrence of economic and social shifts associated with sedentism, when new conditions incentivized organized raiding of settlements. The earliest evidence of prehistoric warfare is a Mesolithic cemetery in Jebel Sahaba, in the Nile Valley, which has been determined to be approximately 14,000 years old. About forty-five percent of the skeletons there displayed signs of violent death.