The simmering debate about the existence of cannibalism is back on the boil with the imprisonment of a Nobel prize-winning believer, Tim Cornwell reports.

Cannibalism is one of the last great taboos, and the source of horrible fascination, puerile and scholarly. Rabbits, chipmunks, hyenas and lions are known to eat their own, but eating people is wrong. Sweeney Todd and Jeffrey Dahmer entered the national folklore in Britain and the United States not merely for killing people but for feasting on them. At the University of Colorado at Boulder, students named their cafeteria the Alfred Packer Grill, after the 19th-century westerner who claimed he was forced to eat six of his companions to survive.

For at least a century, debates about the existence of cannibalism in ancient and modern history have raged in academia. In the 1870s, palaeontologists claimed to have proof. In the 1950s and 1960s, adventurous anthropologists searched for the last lost tribes of head-hunters and people eaters.

Beginning in the late 1970s, by contrast, some scholars debunked historical accounts of cannibalism as colonial myth-making. Travellers' tales from the 17th century were derided as a means of proving the superiority of Western culture.

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Every few years the simmering argument boils over. It is doing so now. Cannibalism, and the proof thereof, was the subject of a recent documentary on American television and a long article in the American academic magazine Lingua Franca. Next year Cambridge University Press is due to publish a collection of papers on cannibalism and colonialism, Cannibalism and the Colonial World, edited by Peter Hulme at Essex University.

The pro-cannibal lobby comes to the table claiming that mounting scientific evidence, from archaeological digs in Europe and across the American South West, shows that cannibalism was practised from 730,000 years ago to fairly recently.

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Christy Turner, at the University of Arizona, says: "We are pretty sure they cut the heads off and roasted them." He has been working in the field since he was fascinated by finding human bones from a site near a Hopi village in north east Arizona 1965 that had all the appearance of food refuse, and is finishing a book for publication.

But the anti-cannibalism camp has also found some encouragement, and this time from a peculiar source: the disgrace of Nobel prize-winner Carleton Gajdusek, the 73-year-old scientist who this month began a prison term for child sex abuse. What they are suggesting, more or less, is that the criminal passions of Gajdusek's personal life raise new questions over his academic work, particularly the exotic territory of his claimed encounters with cannibalism in Papua New Guinea.

Every society forbids anthropophagy, the eating of men, as a horrific crime, but it is clear that not all anthropophagists are equally guilty. Survival cannibalism was practised in desperation by castaway sailors. And members of a Uruguayan rugby team adopted similarly ghoulish tactics to prevent starvation after a plane crash in the Andes.

The rare eating of an enemy as an act of revenge, his heart for his strength, brain for his soul, or even whole body to quiet his ghost, at least carries a spiritual or religious impulse. Most shocking, however, is surely the customary consumption of human flesh for food.

The opening shot in the current cannibalism war was fired by anthropology professor William Arens, at the State University of New York, with his book The Man-Eating Myth: Anthropology and Anthropophagy. Arens accused figures like the 17th-century German explorer Hans Staden of planting the classic scenario of cannibals popping humans in the cooking pot in the European mind set, much as pulp fiction writers of the 20th century would write the lone gunslinger into Western myth. But Arens goes much further than simply suggesting the early explorers embellished their stories. He went out on a limb and said, as he maintains to this day, that cannibalism glibly ascribed to "savages" was a convenient and fearful fiction and nothing more. "I attacked the romanticists who saw cannibals everywhere," he told The É«ºÐÖ±²¥S, explaining his approach. "I think it is a reasonable question, 'do people eat each other?' and I think the answer is no. But I also think it is a reasonable question, why do people think other people eat each other? That is more in the historical record than cannibalism itself. The major historical phenomenon is the idea that people eat each other, not the fact."

Critics say Arens's views are still in the minority among anthropologists. There is too much in the historical record. Go to any run-of-the-mill encyclopedia, for example, and you will find confident references to man-eating in North and South America, and from West Africa to New Zealand. Arizona's Christy Turner was particularly outraged by a critique of cannibalism in prehistory in the Cambridge Encyclopedia of Human Evolution. The entry appeared in 1992, but Turner, 63, talks about it as if it was yesterday. Turner and several published US archaeologists working on the remains and ruins left by the Anasazi Indians have been convinced that cannibalism is "95 per cent" proven. Suggesting that early native Americans were man-eaters is straying on dangerous political turf, however, and Indian scholars have challenged their findings. So has British archaeologist Paul Bahn, who wrote the Cambridge Encyclopedia entry.

Evidence of Anasazi cannibalism from the 12th century was presented at the recent meeting of the Society for American Archeology. Turner identifies five minimum criteria for proving cannibalism through skeletal remains: evidence of cutting with stone tools; breakage of bones around the time of death to expose bone marrow; burning; "anvil abrasions" which can only occur if someone has defleshed the bone; and unusual missing vertebrae, apparently crushed to get the marrow out. Other researchers have reported "pot polish" on bones that were boiled.

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Evidence of cannibalism has also emerged from the caves of Atapuerca, in Spain. Fossilised human bones, dating back about 730,000 years, show evidence of cut marks, it is claimed, where for example the lip muscles were removed from the front of the face. The problem with European and American archaeological finds, however, is the same: that if the remains prove that homo erectus or even homo sapiens was a man-eater, they cannot distinguish a motive. "I know we have got cannibalism," said Turner. "I'm very secure about that. It's the explanation for cannibalism that is still the puzzle."

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The cannibalism debate is not just confined to fossilised bones or historical writing. In Papua New Guinea, circa 1957, American physician and paediatric specialist Carleton Gajdusek arrived to study child development in primitive cultures.

Gajdusek's interest was rapidly diverted to a brain disease, kuru, called "laughing death". Gajdusek would set out to prove that kuru was a slow-acting virus infection, a finding that shed light on Alzheimer's, Aids, and BSE. It would lead him to a Nobel prize.

Central to his research, however, if not to his final results, was that kuru was transmitted among highland tribes by widespread acts of cannibalism, either the eating of a dead person's brain itself, or the handling of it by women and even young children. "We believe that contamination during the cannibalistic ritual was the sole source of transmission of kuru from man to man," he said, in his Nobel lecture.

Gajdusek began his jail sentence in a Maryland prison this month for child sexual abuse. The Washington Post marked the event by publishing details of a phone conversation between the scholar, and one of 56 boys he adopted to live with him in the US. The phone call was made by the young man - now a student at a US university - at the prompting of the FBI, and was taped. It suggested that the man celebrated as a romantic scholar-cum-adventurer, and defended until recently by close colleagues as a generous provider for the youths in his care, was indeed a compulsive paedophile. He named several boys in his household with whom he had had sex, and said he had gone "to the ends of the earth" to find partners, the newspaper said. "I did it with younger kids in cultures in which they're doing it all the time with adults anyway," he said.

Arens, in The Man-Eating Myth, had already taken Gajdusek to task over a photograph that appeared in an article he wrote. It showed a number of adults and children around a cooking pit, with the caption: "All cooking including that of human flesh from diseased kinsmen was done in pits with steam." Queried by Arens, Gajdusek, in a long letter, seemed to admit that the picture was actually a scene of pork being cooked.

"I attended in 1957 and 1958 numerous episodes of cannibalism," he wrote, but added that by the time of his kuru investigations, the impact of a government ban was making itself felt. "Since it was a practice the people wished to hide from government officers, missionaries and Europeans in general, we did not photograph it except on rare occasion." Gajdusek in the past had claimed to have photographs of cannibalism, and to have shown them to small scientific audiences; but described them as too sensitive for general distribution.

Other anthropologists corroborate accounts of cannibalism in Papua New Guinea. Arens, however, suggests that if Gajdusek's sexual proclivities drew him to the country, where he chronicled in his own diaries the homosexual freedoms of young boys, they may at the very least have blinded Gajdusek to possible sexual transmission of kuru.

Lyle Steadman - also an anthropologist at the University of Arizona - visited remote areas of Papua New Guinea in 1966. He became convinced that cannibalism was used as an excuse to kill people said to be cannibals, but that cannibalism was not actually practised. "I never saw a whiff of evidence of cannibalism," he said.

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In 1982, Steadman published an attack on Gajdusek's field work, claiming the scholar's taste for the exotic slanted his views. He, too, questions the lack of photographs. Steadman says he is convinced that Gajdusek "may never really have discovered cannibals".