By Lizzie Wade

Imagine you’re a Yanomamö man, grow-

ing crops and hunting in the Amazon

rainforest of southern Venezuela and

northern Brazil. Someone from your

village has been murdered, and you’re

organizing a raiding party to do a re-

venge killing. Whom do you choose to fight

alongside you?

Your brothers, guessed cultural anthro-

pologist Shane Macfarlan of the University

of Utah in Salt Lake City. But he got a sur-

prise when he and famously controversial

anthropologist Napoleon Chagnon took a

new look at data from Chagnon’s pioneering

studies of the Yanomamö from the 1960s and

1970s. Men who became “unokais” together—

meaning they participated in the same

killing—were largely related by marriage

rather than blood. At best, they were cousins,

and often they were brothers-in-law. Among

married warriors, 70% had a

wife directly related to one of

their co-unokais.

The paper, published on-

line this week in the Pro-

ceedings of the National

Academy of Sciences, offers

a twist on Chagnon’s origi-

nal ideas about how being a

warrior boosts men’s fitness,

and fits current notions

that war is a mode of coop-

eration. “Humans are able

to cooperate even in costly

settings like warfare beyond

the residential community

and beyond kin,” says Sarah

Mathew, an anthropologist

at Arizona State University

(ASU), Tempe, who stud-

ies the evolution of human

cooperation. That’s “a real

exceptional feature of Homo

sapiens,” notes Kim Hill, a

human behavioral ecologist

also at ASU who has studied

small-scale societies in South America.

During 3 decades of living with and

studying the Yanomamö, Chagnon, now

at the University of Missouri, Columbia,

gathered reams of information about their

marriages, wars, alliances, and other rela-

tionships. But some anthropologists said his

1968 ethnography, Yanomamö: The Fierce

People, exploited the tribe by breaking their

taboo on using the names of the dead; oth-

ers argued that the book’s emphasis on

violent encounters helped governments

justify invasions of Yanomamö territory.

Chagnon also faced criticism for infractions

such as giving gifts, including machetes, to

his closest Yanomamö associates, and thus

distorting the social structure he aimed to

analyze. In 2000, journalist Patrick Tierney

even accused him of worsening a measles

epidemic among the Yanomamö as part of a

biomedical experiment. (The American An-

thropological Association, however, cleared

Chagnon of that and most other charges in

2001 and rescinded their remaining criti-

cisms in 2005 [Science, 8 July 2005, p. 227].)

For his part, Macfarlan calls Chagnon’s

data “one of the most unique data sets in

the world,” capturing the Yanomamö at a

time before outside influences had altered

their way of life. Listening to Chagnon’s ex-

tensive recorded interviews with his Yano-

mamö informants assuaged any doubts he

had about data collection, Macfarlan says.

Macfarlan believes that his new view of

how men benefited from becoming unokais

could explain one of Chagnon’s most con-

troversial findings. In 1988, Chagnon re-

ported that unokais of every age had more

wives and children than their nonunokai

counterparts (Science, 26 February 1988,

p. 985). He hypothesized that being a war-

rior gave men high social standing and so

made them more attractive as marriage

partners and fathers. His suggestion that

warfare and violence are “adaptive” be-

haviors that help drive human evolution

quickly attracted fiery criticism.

Some of Chagnon’s ideas are no longer so

startling. But in contrast to Chagnon’s focus

on warriors’ reputations, Macfarlan found

that the key advantage held by unokais

was that they “are plugged into this social

scene” that allows them to make strong al-

liances outside of their immediate paternal

family, often in different villages. That gives

them access to their friends’ female rela-

tives as potential wives. They are “getting

the resources and marriage opportunities

of [their] allies,” not their defeated enemies,

Macfarlan says.

The study shows that for the Yanomamö

and possibly other small-scale societies,

“warfare is about coop-

eration,” agrees Stephen

Beckerman, an anthropolo-

gist and professor emeritus

at Pennsylvania State Uni-

versity, University Park. He

plans a similar analysis of

alliances among the Wa-

orani, another small-scale

society in the Amazon with

a tradition of waging war.

Macfarlan acknowledges

that Chagnon’s data don’t

rule out the possibility

that Yanomamö warriors

formed raiding parties with

men who were already their

in-laws, confirming existing

bonds rather than forging

new ones. In fact, Hill notes,

men in many small-scale

societies often prefer to ally

with their brothers-in-law

because by definition these

men aren’t competing for

access to the same women.

Although Hill doesn’t expect the new

paper to sway any of Chagnon’s most com-

mitted critics, he says it represents “a more

subtle and nuanced view of human society”

than the anthropologist has articulated in

the past. “It’s nice to see Chagnon reanalyz-

ing some of his data 30 or 40 years later

and coming up with a slightly different

view of things.” ■

SCIENCE sciencemag.org

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ANTHROPOLOGY

Friends, not foes, boost warriors’ success New analysis of Yanomamö data suggests that alliances among in-laws raise fighters’ fitness

Controversial anthropologist Napoleon Chagnon lived with the Yanomamö for decades.

31 OCTOBER 2014 • VOL 346 ISSUE 6209 535

NEWS | IN DEPTH

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