Kelly's report was published in the August 30 issue of Proceedings of the National Academy of Sciences.
Era of Warfare
Cooperation among groups allowed for the expansion of early human populations and helped spur migration out of Africa, Kelly says. It also led to new patterns of social organization that eventually led to warpreplanned military attacks on settlements.
The earliest archaeological evidence for organized warfare dates from between 12,000 and 14,000 years ago and is found in Sudan, Africa. In other parts of the world, wars weren't conducted until as recently as 4,000 years ago.
Kelly ties the advent of military warfare to the development of agriculture, which increased the value of territory exponentially. Until then, he argues, most human conflict was like that of chimpssporadic, unplanned fights over turf.
Warfare changed the cost-benefit equation of attacking another group's territory. Tactics such as targeting an enemy's unarmed women, children, and elderly people returned the advantage to the attackers.
Harvard's Wrangham agrees, saying that today's guerrilla wars and terrorismas opposed to "traditional" wars such as World War IIare "a return to 'normal human behavior.'
"Instead of having mutually agreed lethal battles in the style that dominates recent European history, which was not an evolutionarily typical style, we are now exposed to surprise attacks," he said. "Surprise attacks are the human norm, and unfortunately they are effective, costly for the victim group, and hard to defend against."
Kelly believes the recent long period of warlessness among Canada, Mexico, and the United States provides a ray of hope.
"The U.S. was at war with Canada in 1812 and with Mexico in 1848 but has managed to live in peace with its neighbors for the past 150 years," he said. "So we clearly have the capacity to maintain peaceful relations with neighbors over extended periods."
"These capacities are as much a product of [human] evolution as the capacity to engage in lethal intergroup violence."
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