Scientific evidence for warfare has come from settled, sedentary communities. Some scholars argue humans may have a predisposition for violence (chimpanzees, also great apes, have been known to kill members of competing groups for resources like food), placing the origins of organized violence prior to modern settled societies. However, actual evidence suggests that organized, large-scale, militaristic, or regular human-on-human violence was absent for the vast majority of the human timeline, and is first documented to have started only relatively recently in the Holocene, an epoch that began about 11,700 years ago, probably with the advent of higher population densities due to sedentism. Social anthropologist Douglas P. Fry writes that scholars are divided on the origins of this greater degree of violence—in other words, war-like behavior: