In tribal societies, one might expect that the fiercest warriors get the most women and father the most children. But that's not necessarily the case, says a new study of the brutal Waorani tribe of Ecuador. The most aggressive Wao warriors have about the same number of wives and children as milder-mannered men have, and their children are less likely to survive beyond the age of 15, largely due to an endless cycle of revenge killings.
The Waorani are one of the most homicidal tribes ever studied. Located in a region just south of the Napo River, the place where the Andes Mountains meet the Amazon Basin, the tribe is preoccupied with revenge. Young Wao men are encouraged to develop a ferocious reputation early on, and before long they start raiding. The tribespeople constantly recount stories of these raids in gruesome detail, noting who was responsible and who needed to be avenged. Half of all Waos die violently.
Studies of a similarly murderous tribe, the Yanomamö of nearby Venezuela, suggested that such homicidal behavior conveyed an evolutionary advantage. In a 1988 paper in Science, anthropologist Napoleon Chagnon, now a professor emeritus at the University of California, Santa Barbara, found that the most aggressive Yanomamö men had higher prestige within the tribe, which led to them having more wives and children, than less-aggressive men.
The new study argues that the picture is not so clear-cut. Lead author Stephen Beckerman of Pennsylvania State University, University Park, and colleagues interviewed 121 Waorani elders to compile histories of 95 of the tribe's warriors. (The Waorani are much more peaceful today than they were in the past, possibly due to Christian missionaries, who first made contact in 1958.) The team defined highly aggressive men as those who took part in more than four raids over their lifetimes; some of the most violent warriors fought in as many as 16 raids.
Beckerman's group found no significant difference in the number of wives or children between highly aggressive Wao males and less aggressive males. What's more, the most aggressive warriors had fewer children survive past their reproductive age--about 15 years old--than the more peaceable Wao men had, the researchers report online today in the Proceedings of the National Academy of Sciences. The findings show that, at least for the Waorani, it's actually less advantageous to be murderous, because so many of a warrior's children wind up dead before they can reproduce.
Co-author and retired anthropologist James Yost says revenge killings are responsible for the vast majority of deaths among Waorani children. And that could explain some of the differences seen between the Waorani and the Yanomamö tribes, says Yost, who spent much of his working life living with the Waorani. Yanomamö culture dictates that after a spate of killings, both sides must stand down for about a generation. During peacetime, more murderous warriors enjoy an elevated status, having more access to women and allowing their children to survive to reproductive age. But the Waorani have no such "downtime" rule, he explains. Beckerman says that the new work should caution anthropologists against extrapolating too much from a single tribe's behavior. "The most important thing about our study is that it shows Chagnon's results cannot be general to [all] tribal people," he says.
Chagnon says the study makes important strides in understanding tribal warfare. But he calls the team's methodology "fuzzy," saying, for example, that Beckerman's group defined aggressiveness in an arbitrary way. That makes it difficult to compare these findings with those from the Yanomamö tribe, Chagnon says. "I do not think they have confirmed or refuted my conclusions; ... we have measured different things."