A book on the work of two American anthropologists has divided the profession with claims that they destroyed the way of life of hundreds of Yanomami Indians. Tim Cornwell reports.

The much-studied Yanomami, a tribe that lives deep in the Amazon, were introduced to the rest of the world in the mid-1960s as a prehistoric people protected by their remoteness. They were "virgin soil" for anthropologists, their way of life a time capsule from the distant past.

A quarter of a century later, as Arizona anthropologist Kim Hill discovered, they had very much lost their virginity. In the late 1980s Hill, a veteran of South America, married to a Venezuelan, was contemplating a research project among the Yanomami. He recalls the hostile reception that met him when tribe members discovered he came bearing free medical supplies, but no gifts. One man warned him in threatening terms not to come back. "The Yanomami have been pretty spoiled," says Hill. Despite being a primitive people, it did not take very long for this Stone Age tribe to discover the uses of steel.

Raymond Hames, of the University of Nebraska, has spent 38 months in the field with the Yanomami on three trips, dating back to the mid-1970s. "Everybody who wants to work with the Yanomami distributes steel goods," he says matter-of-factly. "Axes, machetes, fish hooks, aluminium pots, fishing line. Cloth for loin cloths. Sometimes beads. Many things that make their lives more efficient. You would try to make sure that most of the families received a machete."

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Missionaries, mining interests, measles, and the Venezuelan government are all blamed for the precipitous decline of the Yanomami, whose population and territory have dwindled under the forces of globalisation. But the question of what anthropologists added to the mix may explain the convulsions in the profession over a forthcoming book whose facts are hotly disputed. Its chief target is Napoleon Chagnon, a larger-than-life figure whose work with the "fierce people", as he calls them, is included in introductory anthropology courses world wide.

The book in question is Darkness in El Dorado: How Scientists and Journalists Devastated the Amazon by Patrick Tierney. Tierney's last non-fiction book, The Highest Altar: A History of Human Sacrifice , was published in 1989. Advance proofs of his latest work are whipping round the profession like hotcakes, along with a landslide of emails and personal attacks. An extract has been published in The New Yorker magazine, and the book's allegations reported in The New York Times .

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A spokeswoman for publisher Alfred Knopf cautions that the finished book might differ from the proof, but declines to say how. After several delays, Tierney's book is scheduled for publication in mid-November, nicely timed for the annual meeting of the American Anthropological Association in San Francisco. There are at least four separate inquiries or investigations into its contents under way.

Spokesmen for the American Anthropological Association, meanwhile, are falling over themselves to insist that standards have changed since Dr Chagnon's first encounters with the tribe.

In one of his first extended interviews since the story broke, Chagnon fired back at Tierney. Tierney has dogged him for five years, he claimed in the interview, feeding disparaging material to the South American press in advance of his research trips, persuading officials to cancel travel permits at the last minute. He accuses Tierney of "completely distorting virtually all my research", and of working hand-in-glove with the Silesians, Catholic missionaries whom he regards as his old foes in the region. "I'm a pretty ordinary guy," he says, though by most accounts he is anything but. "To be compared to Josef Mengele, that's not something I would like to introduce myself by."

It was two scholarly supporters of Tierney who made the Mengele allusion, in an email talking about genocide and alerting fellow anthropologists to the book. Tierney's most incendiary charge is that in the first three months of 1968, as Chagnon travelled Yanomami territory with his late colleague James Neel, their progress closely matched that of the worst epidemic in Yanomami history, a fatal outbreak of measles in which hundreds died. Tierney suggests that Neel, while crudely collecting genetic data on the Yanomami in a study funded by the US Atomic Energy Commission, brought to the Amazon a measles vaccine that fuelled the outbreak.

In The New Yorker excerpt, Tierney insinuates rather than states his case in a rhetorical style that combines events but does not connect them. The article notes that "it cannot be determined with any accuracy how many died after receiving the vaccination", and registers the medical consensus that the vaccine "was not, in itself, contagious". This hedging has not quite made it into the news reports of the book. The BBC, for one, broadcast a report in English, Spanish and Portuguese that "a US geneticist who died earlier this year has been accused of deliberately infecting thousands of Yanomami Indians with measles, killing hundreds of them", a line echoed by other media outlets.

Neel was a respected University of Michigan scientist who died in February. The measles charge has been met with some fairly persuasive rebuttals that do no favours to Tierney's reporting. Tierney notes that Neel "had his researchers" administer the vaccine to 40 tribespeople without the recommended gamma globulin dose to reduce the fevers it can cause. The University of Michigan, in a statement, says contemporary sources in fact show that Neel, who had requested 2,000 doses of the vaccine when he heard of the measles outbreak, personally administered 1,000 doses, all except the original 40, with gamma globulin. "We believe that Mr Tierney has not consulted important original source material that was readily available for review," the university states.

Chagnon, now retired to Michigan, is described as a mixture of the brilliant and the abrasive, a man who unashamedly racked up personal, political and intellectual enemies. His career was made among the Yanomami with pioneering documentary film and videotape, backed by a phenomenal outpouring of research articles and books.

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The thrust of his work was Yanomami warfare and what it implied for the evolution of human nature. One of his most famous films is The Ax Fight . Among the Yanomami aggression was a key to reproductive success, Chagnon concluded. The drift of his conclusions, often cited by sociobiologists such as Steven Pinker and E. O. Wilson, took him into contentious territory.

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But it is the photographs accompanying The New Yorker story, titled "The Fierce Anthropologist", that convey the thrust of Tierney's assault on Chagnon. In one, the intent young bearded researcher is shown in 1968 posing self-importantly in Yanomami loincloth, face paint, feathered shoulders, his fist wrapped around a clutch of spears. In another, taken 20 years later, he poses happily at the keyboard of his solar-powered laptop with a group including warriors and a bare-breasted, pierced-nose Yanomami woman.

The message is plain: that Chagnon was lording it in the jungle, playing out his own fantasies. In the text, American anthropologist Kenneth Good is quoted calling Chagnon "a hit-and-run anthropologist who comes into villages with armloads of machetes to purchase cooperation for his research". While claiming in his hugely successful book, The Fierce People , that Yanomami warfare was largely a question of men competing for women - giving the successful the genetic advantage - Chagnon's gifts of machetes and axes were both a windfall and a provocation, it is alleged.

It is claimed that Chagnon indulged in yopo , a local hallucinogen, and bribed children for tribal secrets. For one film The Feast , he is described as more or less using an abandoned village as a stage set. In the early 1990s, it is said, Chagnon took journalists and scientists on helicopter tours of the region to build support for a Yanomami reserve. Structures in three villages, it is claimed, were badly damaged by downdraft from the choppers.

Chagnon takes angry issue with one "distortion". He used ebena - the Yanomami word for yopo - only once or twice, he said. Once was in a run-in with a Protestant missionary, he said. "The Indians asked me to," he said. "They were afraid that this particular missionary was able to throw them into the chasm of hell. He was intimidating them. I said we are going to take care of that right away."

Accordingly he took the drug and "pranced and danced to speak to the spirits", he said. "It was purely to make a particular point that the missionary didn't have the authority to put these people in hell." Chagnon says he wrote the incident into one edition of his book but later withdrew it.

As to the machetes, he says, "I have probably given fewer away than most of the missionaries have. The Yanomami are a contentious people but I have never seen them become bitter over the way in which trade goods were distributed. I always used the headman of the village to tell me who to give them to." Anthropology, says Chagnon, has "gone beserk. It's gone postmodern. Postmodern scholars don't like science."

While his work has always been controversial, after 30 years in print, he says, his book is now paraded as "disgusting, or irrelevant or exploitative". He remembers his first sight of a Yanomami village, of a dozen burly tribesmen pointing their arrows at him, of sharing a bowl of hot plantain soup with the village head man.

Thomas Headland, of the Summer Institute for Linguistics in Texas, has done linguistic research with tribal communities around the world. "I wouldn't mind seeing Chagnon knocked off his pedestal because he is no friend of mine," he says.

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But as Headland read Tierney's book, scouring each paragraph plus all 1,599 end notes, he says he grew increasingly uneasy. The book has a rhetorical style, he says, and he compares its approach to saying that someone was in a bar but never proving that he was an alcoholic. Tierney, he adds, was unrelenting in his attempt to go through the garbage. "These are very serious allegations," he says. "Accusing anthropologists of murder and genocide and faking data."