Roscoe has extensively studied revenge as a motive for war among tribes in New Guinea and concludes that killing enemies to avenge the death of kin - something only humans do - is probably not a useful evolutionary adaptation. This is because lethal revenge most frequently fuels more killing rather than deterring it, says the professor of anthropology and cooperating professor of Quaternary and Climate Studies at UMaine.
"I argue that revenge is probably not an adaptive feature because revenge is not good for you," Roscoe says. Evolutionarily speaking, it does not make sense to engage in behavior that may not only kill yourself but also other members of your clan or tribe. Writ large in a thermonuclear exchange, revenge killing could theoretically wipe out your entire species. "It makes evolutionary sense to fight and then back off."
Humans have, in a sense, deviated from the evolutionary path by engaging in revenge killings and warfare. They do so because their technical ability to harm one another has outpaced their social and cultural abilities to deal with behavior that might not be so wise, Roscoe surmises. Only in the last 10,000 years of human existence have people evolved from hunters and gatherers with spears to glorified hunters and gatherers with thermo-nuclear weapons.
"We may have nuclear technology, but we still have stone-age brains," Roscoe says. "Our social and political systems are slow to adapt in comparison to the pace of technological development."
Previous theories on motives for revenge, based on socio-biology, have centered on an escalating tit-for-tat complex. This theory holds that humans have simply taken behavior routinely practiced by other animals to the next step. Many animal species engage in escalating aggressive behavior. Male red deer competing for territory or mates, for example, will first roar at one another. If neither backs away, the animals then walk back and forth side-by-side sizing one another up. If this fails to resolve the conflict, the two animals may fight, but the results are typically not lethal.
Humans, however, are the only animals to seek out enemies and to kill them for past actions. Roscoe argues that this is because humans have a large, highly developed neo-cortex, the region of the brain known for intellectual thought and creativity. The neo-cortex is believed to have evolved for positive purposes such as enabling humans to develop tools, to communicate through language, and to plan cooperative hunting trips. However, it has not always been used for positive purposes.
"Humans developed the ability to model actions before they happen. This means we can plan collective violence. It explains why we have warfare," he says. Research on chimps confirms that, once you can gang up and launch a surprise attack on outnumbered victims, killing becomes a dramatically more attractive option than it is in the one-on-one confrontations typical of other species.
The neo-cortex also allow humans to manipulate their emotional states. Warriors, for example, can whip themselves into an angered frenzy by recalling slain kin and engaging in repetitive, war-mongering chants.
A highly developed neo-cortex also allows people to de-humanize their enemies. Many tribes in New Guinea, for example, refer to their enemies as "our game" and world leaders have equated their enemies with mad dogs and rats. This is how humans circumvent their built-in aversion to killing members of their own species, Roscoe says.
This portion of the brain has also allowed humans to develop sophisticated weapons whereby they can kill one another without face-to-face contact. This not only can make killing more efficient, but also gets around our in-bred aversion to killing other humans.
Roscoe has focussed his research on tribes in New Guinea because surprisingly little work has been done on the wars waged by these people, many of whom did not have contact with outsiders until the 1930s. In addition, the island presents a potential treasure trove of information on warfare because, at the time of contact, there were thousands of groups that spoke more than 1,000 languages. These groups were often at war with one another. With funding from the National Science Foundation, Fulbright-Hays Area Studies Program and the American Philosophical Society, Roscoe has traveled to archives around the world to collect data about warfare in contact-era New Guinea. Since anthropologists usually arrived many years after contact, Roscoe often has had to rely on other sources, especially the writings of missionaries who visited the South Pacific island. Much of the writing Roscoe reviewed is in German and Dutch.
He found that much of the warfare in New Guinea was, in fact, precipitated by revenge and that the motive was to weaken the enemy and to forestall further aggression. Some tribes believed they must fight until the number of dead on both sides were equal. Others believed they must inflict lethal revenge to be spared from the ghosts of clansmen who were killed. However the fighting began, it often escalated, sometimes involving groups not party to the initial clash, and continued for generations. This raises problems for theories that revenge stops further aggression.
"My hope is that somewhere down the road, we will use this knowledge to get around killing one another. War is the most costly thing in the world in terms of blood and treasure. We need to figure out why we have war before it wipes us off the planet," Roscoe concludes.
The annual meeting of the American Association for the Advancement of Science, the world's largest interdisciplinary scientific gathering, will draw more than 6,000 individuals from all over the world to Denver.