for National Geographic News
The invention of the spear about a million years ago sparked 985,000 years of relative peace between tribes of early humans, according to a recent report.
This advent of weaponry also marked a split in the behavioral paths of chimps and humans, says the report's author, Raymond C. Kelly, an anthropologist at the University of Michigan in Ann Arbor.
Studies by Jane Goodall and others show that if a group of chimps from one community spots an individual from a neighboring group, they stalk and kill the trespasser.
This type of violence occurs almost exclusively among adult males in border areas where two or more groups hunt for food. The killing is opportunistic and is done to establish territorial dominance.
Strength in numbers benefits the group attacking and outweighs the attackers' risk of injuries or fatalities.
Early human behavior followed this pattern until about a million years ago, when humans invented throwing weapons to hunt large mammals, Kelly says. The ability to kill from a distance and the use of ambush tactics significantly affected border interactions.
The size of a group was no longer a guarantee of success, and the potential of being seriously wounded or killed increased.
Kelly believes the change in circumstances forced early humans to come up with new ways to resolve conflicts and to maintain friendly relations.
The anthropologist cites the Andaman Islanders of India, which he studied for decades, as an example. On the part of the islands where neighboring groups had friendly relations, a territory of 16 square miles (41 square kilometers) supports 45 people.
But in the part of the island where there was conflict between neighbors, a territory of the same size supported only 33 people. The larger population size would mean the cooperative groups contributed more genes to subsequent generationsmeaning that there was an evolutionary advantage to peaceful relations.
Others are skeptical that more weaponry would reduce violence.
"Maybe it did, but it seems to me unlikely to have done so," said Richard Wrangham, an anthropologist at Harvard University in Cambridge, Massachusetts. "It is easier to make surprise attacks with weapons than without, and hard to defend against them."
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