Wired for war?
Killer chimps fuel debate on how war began
Posted Feb. 9, 2005
Special to World Science
In 1998, researchers in Uganda stumbled on a group of male chimpanzees beating on and swaggering around another male chimp’s freshly killed body. Its windpipe, fingernails and testicles were torn out.
The finding added to a growing number of documented incidents of chimpanzees ganging up on, hunting down and killing each other—activities in which some researchers find eerie parallels to human war. These scientists argue that the killings among chimps, our closest ape relatives, may offer clues to war’s evolutionary origins, lessons that could help us break our own violent habits.
But this claim has stirred a backlash from other scientists, who dispute its apparent implication that we’re biologically wired for war. Some of these critics prefer to blame the mass killing on various aspects of modern civilization—a force, they add, that may also be pushing chimps to mutual violence by eating into their habitats and food resources.
New findings could fuel the debate.
Two new reports of violence among chimps have appeared, leading their authors to claim that this activity is normal for the animals.
“Lethal coalitionary aggression is part of the natural behavioral repertoire of chimpanzees,” writes David Watts of Yale University in New Haven, Connecticut, in one such report, scheduled to be presented April 9 at the Annual Meeting of the American Association of Physical Anthropologists in Milwaukee, Wisconsin.
The other appeared in the June, 2004 issue of the International Journal of Primatology. Combined, the reports documented 11 killings and some maimings in two chimp communities totaling over 200 members. Each report covers a period of slightly under a decade.
There is an online
movie of a chimpanzee attack,
filmed in Tanzania in 1998, which gives an idea what the incidents are like,
researchers say. It’s unknown
whether this assault actually killed its victim, a young male.
Watts declares the incidents back up a proposal that war is rooted in evolution. This view, called the imbalance of power hypothesis, holds that animals that conduct mutual group violence do so because it helps them win resources and territory. This in turn lets them survive longer and breed more—and all living species, evolutionary theory holds, descend from those that were able best do those things in the past.
The imbalance of power hypothesis states, in other words, that evolution favored humans and chimps who warred when and because they could get away with it. “This makes grisly sense in terms of natural selection,” said Richard
Wrangham, a professor of anthropology at Havard University in Cambridge, Mass., and the author of the hypothesis.
Human and chimp battles differ in major ways, he acknowledged. Humans seem to be much worse judges what they can get away with. The result: human wars often drag on year after bloody year, after having been initially sold to those involved as an easy win.
But there are also similarities to chimps, Wrangham added. Fundamentally, “if we as human males feel we are in a position to kill safely, then we tend to do it,” he said. One example may be genocide, he said. Insurgents in Iraq often attack on one or a few isolated victims, not unlike the chimps, who usually gang up on one, he added. “The old principle of attacking safely is still there.”
The modern phenomenon of drawn-out, bloody wars might be a result of the fact that leadership decisions have moved away from the battlefield, Wrangham speculated, adding that he’d rather leave this issue for future research to address.
But none of this contradicts his view, he added, that warfare as a whole is rooted in tendencies like those the chimpanzees display. Among hunter-gatherers, “the surprise raid is the typical pattern. The aim is to get together a small group of men who go off, and find a helpless victim, kill them and run away again.”
But some anthropologists denounce parallels between human and chimp violence.
The frequency of chimp killings “has been exaggerated,” said Brian Ferguson, a professor of sociology and anthropology at Rutgers University in Newark, N.J.
The first reports of chimp violence came in the 1970s in Gambia and later in Tanzania, he said, when whole chimp communities were supposedly wiped out by others. “But all we know for sure is that some chimps disappeared,” he said, adding that some researchers have “a tendency to take a disappeared chimpanzee as a killed chimpanzee.” Some of the animals might have just left, he added.
A possibly darker dimension to the tale is that human interference might have induced the violence, Ferguson added. This might have occurred because human activities put pressure on the chimps’ land and food resources, forcing them to duke it out over the dwindling remains.
The worst of the environmental depradations at the national parks housing the chimps in the studies, such as logging, seem to have ended, Ferguson added; but human pressure continues. For instance, he said, forest cover for chimps has vanished all around Kibale National Park, home of the chimps in Watts’ study, who accounted for eight of the 11 killings mentioned in the two new reports.
“They’re totally hemmed in now,” Ferguson said of the chimps at Kibale. “It’s a very human kind of situation: a population that’s growing, that can’t go anywhere, is beginning to run down its resources.” The Ngogo chimp community, the one Watts reported on, is gigantic for a chimp community, he added; researchers have estimated its membership at more than 150.
If modern civilization is pushing chimps to do battle with each other, it wouldn’t be a totally unprecedented finding. It would fit a widely believed theory that war is basically a product of modern civilization. This view, first popularized by the French philosopher Jean-Jacques Rousseau in the mid-1700s, got a boost in 2002, when new research suggested Native Americans had been more peaceful before Europeans landed in America than afterward.
Anthropologists at the University of California at Santa Barbara and Ohio State University examined more than 5,000 Native American skeletons and found that those from after Christopher Columbus landed in the New World showed a rate of traumatic injuries more than 50 percent higher than those from before. Some researchers speculated that the increased violence evident in the bones might have stemmed from such factors as disputes over access to Western goods and weapons, and White people’s expansion forcing once-separate groups of natives together.
Regardless of these findings, chimpanzee researchers dispute the claim that modern man’s intrusions are the main culprits in chimp infighting.
The Kibale park covers more than 700 square kilometers, and the chimps in it multiply as rapidly or slightly more than average, suggesting resources are ample, Wrangham argued. “They actually seem to be very well off in terms of their food supply.”
He also dismissed Ferguson’s idea that researchers are counting too many unconfirmed disappearances as killings. Two-thirds of the 49 killings documented to date were either directly seen, he said, or inferred from clear evidence such as chimps prancing around a brutalized corpse. Only the remaining 11 are classified as suspicious disappearances.
Some researchers have also disputed the balance-of-power hypothesis on grounds that mutual killing among animals besides chimps and humans is rare. None has been found among
bonobos, apes more closely related to chimps than humans are.
Wrangham argues that this may be because only particular social structures, such as a combination of social communities with small and frequently changing subgroups, make slaying an easy option. “It is a finely tuned strategy,” he said, “used, on occasion, when killers are able to kill at very low risk to themselves.”
Send us a comment
on this story, or send
it to a friend