Violent conflict offers biological benefit

Violent conflict may, under certain conditions, offer a biological benefit to those who take part in it, a new Harvard study has found.
Researchers found that among members of an East African herding tribe, those who engaged in conflict - in the form of violent raids carried out on neighbouring groups - had more wives, and thus more opportunities to increase their reproductive success through having more children.
"The currency of evolution is reproductive success. By having more wives you can have more children. What we found was that, over the course of their lives, those who took part in more raids had more children," said study author Luke Glowacki.

Importantly, though, that benefit - the increased reproductive success enjoyed by raiders - is mediated by powerful cultural forces, said Glowacki, a doctoral student working with Richard Wrangham, Ruth Moore Professor of Biological Anthropology and Curator of Primate Behavioral Biology in the Peabody Museum of Archaeology and Ethnology.
"It's very clear what the pathway to greater reproductive success is - it's access to livestock, which are obtained through raiding and then used for marriage," Glowacki said.
"But the cultural mechanism is mediated by the elders who control virtually all aspects of the society. After a raid young men give any livestock they capture to the elders and the raider cannot use them at that point even if he wants to get married.

"Later in life, as the raider gets older he can gain access to them, so there's a lag in receiving benefits from participating in a raid," Glowacki said.

Glowacki lived with the Nyangatom, a group of nomadic herders living in a region of southwest Ethiopia and South Sudan, for more than a year.
Typically carried out by Nyangatom men between 20 and 40 years old armed with weapons like AK-47 rifles, the raids sometimes result in serious injuries and deaths.
Those who take part in the raids, however, must turn over any livestock they obtain to village elders, who use them to obtain wives for themselves.

It may not be until years later that elders agree to provide a raider with the cows necessary to obtain their first wife, or subsequent wives.
"In many cultures, particularly in east Africa, in order to get married you have to give livestock to the bride's family - we refer to it as bridewealth," Glowacki said.
Glowacki conducted interviews about the raids, and collected reproductive histories by asking how many wives raiders have, how many children each has had, how many are alive, how many died and how they died.
In an analysis of 120 men, Glowacki said, the data was clear - those who participate in more raids had more wives and more children over the course of their lives.

But while raiders did benefit from taking part in conflict, the lack of an immediate payoff, Glowacki believes, helps to keep violence in check.
The study is published in the Proceedings of the National Academy of Sciences.