Published online 11 May 2009 | Nature | doi:10.1038/news.2009.463

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Making war not love

Fiercest warriors in Amazon tribe left fewer descendants.

Waorani man with blowgun.More aggressive Waorani men may not father more children.James Yost

The most warlike men in an Amazonian tribe fathered fewer children than their milder fellows, say researchers. The finding shows that bellicosity need not always have evolutionary advantages, and that the social consequences of violence depend on cultural context.

The Waorani are a semi-nomadic group living in the Amazon rainforest of Ecuador. Peaceful contact with missionaries was established in 1958, and the group has lived in relative calm since the early 1970s.

But genealogical studies suggest that before this change in lifestyle the Waorani had the highest homicide rates ever recorded, with 54% of men and 39% of women dying violent deaths at the hands of other Waorani.

Most were killed in blood feuds going back generations, which could reignite over almost anything, says cultural anthropologist Stephen Beckerman of Pennsylvania State University at University Park, who led the team.

"There was no concept of accidental death or injury," he says. "If I'm out hunting and a tree branch falls and almost hits me, that's witchcraft. Somebody caused that to happen, and I have to kill him and his wife and children and mother and father and all his brothers and sisters." Raiding parties would ambush their victims at night, killing them with spears.

“There was no concept of accidental death or injury.”

Stephen Beckerman
Pennsylvania State University

To see how this violence related to men's family lives, Beckerman and his colleagues interviewed 121 Waorani elders aged over 50. They obtained the raiding and family histories of 95 warriors, either directly from the men themselves or from the reminiscences of relatives.

Men who took part in an above-average number of raids didn't have more wives, or more children, they found. In fact, the children of such men were less likely to survive to adulthood than those of less aggressive men. The results are reported today in the Proceedings of the National Academy of Sciences1.

Counter-case

The new study contrasts with one of another Amazonian tribe, the Yanomamö, where men who had killed in raids had more wives and offspring than those who had not2. "We thought that if any culture was going to give a case for the generality of that finding, it would be the Waorani," says Beckerman. "But it turns out they're a counter-case — it shows the importance of cultural context."

The Waorani study is a valuable contribution to an area about which we know very little, says primatologist Richard Wrangham at Harvard University. But, he adds, there may be other forms of aggression besides raiding, such as a short temper, and other measures of reproductive success, such as children fathered on women other than one's wives, or the survival of siblings, nieces and nephews. "It would be premature to use this study as the basis for strong conclusions," he says.

Rather than interview retired warriors, we might do better to compare contemporary soldiers and civilians, says anthropologist Robert Borofsky of Hawaii Pacific University in Honolulu.

"For most studies — and certainly for the Waorani — the data are generally retrospective, based on memory, or on genealogies which may or may not be accurate," he says. "The only way to move beyond speculative generalizations is to study a broad sample of real people living actual lives today."

Vicious cycle

The Yanomamö seem to have been less violent than the Waorani. But the difference between the dynastic fates of the two tribes' warriors may be down as much to the timing of the violence as its amount, says Beckerman. In Yanomamö feuds, about a generation passed between each round of bloodletting — giving warriors a chance to marry and father children. The Waorani had no such temporary truces.

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So why were the Waorani so violent? A fierce reputation seems to have neither won prestige within the group nor deterred attack from outsiders.

The tribe may have just become trapped in cycles of revenge, says Beckerman. "They were almost certainly en route to killing themselves off when the missionaries got there," he says. "When the missionaries said 'God wants you to stop killing', they got the impression that there was a collective sigh of relief."

The tribe's history shows the malleability of human behaviour, says Wrangham. "It's a classic example of how quickly humans can change patterns of violence." 

  • References

    1. Beckerman, S. et al. Proc. Natl Acad. Sci. USA 10.1073/pnas.0901431106 (2009).
    2. Chagnon, N. A. Science 239, 985–992 (1998).
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