Over a period of 1,200 years, violence in what is now central California was highest in regions where resources were scarce, a new study reports. The research finds no relationship between levels of violence and the complexity of the social structure of a region.
Anthropologists have spent much effort debating whether our pre-agricultural ancestors were more or less violent than modern societies, and the causes of those wars that did occur. The answer could hold important implications as to how we can reduce violence today, but it often appears that the discussion is based more on the prejudices of those taking part than actual evidence.
A team led by Dr Mark Allen of California State Polytechnic University, Pomona has tackled this question using thousands of bodies dug up in central California, mostly around the Bay area, dating from 1,530 to 230 years ago. These were compared with what we know about environmental conditions and social structures when each individual died.
Overall, 12.4 percent of the bodies show signs of suffering injuries from violence. The proportion of individuals whose bones preserved signs of violence rose at times, and in places, where environmental productivity was low.
In Proceedings of the National Academy of Sciences Allen and his co-authors present two possible explanations for this. The more obvious is that when food or other resources are hard to come by people are more likely to fight over what little is available; the risk of dying in battle might be better than starving to death.
An alternative explanation uses the fact that areas of low productivity were probably inhabited by small numbers of people ranging over large territories. Although they may have had as much food as their counterparts in more fertile areas, the inhabitants would have seen less of their neighbors, and therefore failed to create the bonds that might prevent violence.
A competing hypothesis for the causes of warfare blames hierarchies. Where leaders have the authority to order others to do battle on their behalf, bloodletting may increase. Although possibly true for agricultural or industrial civilizations, Allen found no association between levels of violence and the complexity of social structures in the foraging populations he studied.
Technology did play a part, however. Death rates from sharp object trauma increased after the introduction of the bow and arrow to California 1,000 years ago, presumably with the reassurance that “bows don’t shoot people, people shoot people”.
Intriguingly, there were very different patterns observed for different sorts of injuries. All the increase in violence in conditions of low productivity was in the form of sharp object trauma, which was seen in an average of 7.4 percent of skeletons. Rates of blunt object trauma were more stable and seemed unaffected by environmental or social conditions.
Sharp object traumas usually seems to have caused, or been closely associated with, death. On the other hand, most cases of blunt object trauma appear to have been non-fatal, often having occurred long before the individual died.