ONCE every few months, a greying and respectable Indian scholar named Trilokinath Pandit travels by launch to a jungle island in the Andaman Islands where the inhabitants strip him naked and steal his glasses. This is Mr Pandit's job as an anthropologist, and he loves it.

'I'm privileged to have this contact with the tribesmen,' said Mr Pandit, a director of the Anthropological Survey of India. 'Before, it was worse. They shot arrows when we tried to land.'

The Sentinelese, as the islanders are known, live on North Sentinel, one of a chain of islands in the Bay of Bengal. Their skin is ash-black and their faces moon- shaped with negroid features.

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They can husk coconuts with their teeth, and use fire, which they hide and guard jealously because they do not know how to make it. With long bows and arrows tipped with iron salvaged from shipwrecks, they are superb marksmen. Farming is unknown to them. They survive on fish and turtles, and hunt wild pig and the huge monitor lizards that abound on their island, an area of a mere 30 square miles.

Sentinelese songs contain just two notes, and they can only count up to two, above which they call everything else many. Their only form of art is body painting, which consists of wavy smears of white or ochre.

More than 100 of the Sentinelese live in palm-built lean-tos around the island, yet they have no community structure, no chiefs and no witchdoctors. Their way of life is comparable to that of humans 15,000 years ago; it is possible that they have not evolved any further because they simply have not been required to do so.

It took Indian anthropologists 24 years to befriend the islanders with gifts of coconut and iron chunks. But now that they have succeeded, Mr Pandit and his team are hesitant about how - or whether - these tribesmen should be 'civilised'.

'Permanent isolation isn't practical,' he said. 'They're surrounded by 200,000 people living in these islands. But the government has to make sure they're not harmed, and that they don't die from imported diseases.'

The Sentinelese are not the only aboriginals left in Andaman, a chain of 361 islands stretching between India and Burma. Other aboriginals are hidden in the jungles, such as the Andamanese, the Onge and the Jarawa. But the Sentinelese have resisted contact the longest.

When the British set up penal colonies in the Andaman Islands in the 1850s, the tribal population was estimated at about 5,000. The aboriginals resented the foreign intruders and fought back with their puny weapons. The British responded by slaughtering many of them, and today, fewer than 400 aboriginals are left.

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For many centuries, sailors viewed the Andaman Islands with dread: tales drifted back of shipwrecked survivors being eaten by cannibals. Mr Pandit claims, however, that the Andaman islanders never dined on their victims. They do, however, like to hang the jawbone of a favourite relative around their necks.

Despite the many arrows shot at him, Mr Pandit insists the reputation of the Sentinelese for hostility is unfair. 'They're cautious, that's all. They want to defend themselves against outsiders.'

The islanders cannot be oblivious to the forms of civilisation that surround them; freighters pass by on the horizon and planes across their skies. They make occasional forays in dugout canoes to hunt turtles or fish, but they don't seem to sail far out of sight of North Sentinel.

Their aggressive isolation seems self-imposed. 'I'd give my right arm to know what they're thinking,' said Mr Pandit, 'but we just haven't learned enough about them yet.'

When the first anthropological expedition reached the island in 1967, the Sentinelese hid in the jungle. When teams returned in 1970 and again in 1973, the scientists were greeted with a hail of arrows. Then in 1974, the anthropologists tried a different tack: they brought gifts of coconuts, pots and pans, and a live pig, and left them on the beach.

But the Sentinelese were not so easily bought. Warriors with bows, arrows and spears lined the shore, posturing in defiance, and Mr Pandit recounted in a report: 'Sometimes they would turn their backs to us and sit on their haunches as if to defecate. This was meant to insult us and to say we were not welcome.'

Unruffled, the anthropologists kept dropping gifts on the island, and the Sentinelese progressively grew less hostile and more playful. They love coconuts, which do not grow on North Sentinel.

Finally, on 4 January 1991, Mr Pandit and his colleagues were met on the beach by a party of 28 men, women and children, for once unarmed. 'They may not have chiefs, but a decision had obviously been taken by the Sentinelese to be friendly towards us,' Mr Pandit said. 'We still don't know how or why.'

Now, the anthropologists have learned to remove most of their clothes, watches and spectacles before visiting the Sentinelese and the Jarawa, another isolated tribe. 'I've lost half a dozen pairs of glasses,' lamented Mr Pandit, who has been stripped naked by the islanders on several occasions. 'Clothing doesn't make much sense to them,' he said. 'They're curious about what we're trying to hide underneath.'

The anthropologists now practise the traditional Sentinelese greeting, which is to sit in a friend's lap and slap your right buttock vigorously.

A debate is raging among scientists and Indian officials about how the Sentinelese should be treated. Some want them drawn into civilisation as rapidly as possible. But other Andaman tribes have been cruelly exploited: their women have been inveigled into brothels as exotica, the men coaxed away by opium and alcohol to trade in the edible birds' nests that the Chinese consider to be a delicacy.

So far, the Indian government has banned all visitors to the island and forest areas where the aboriginals live. 'We can't leave them forever,' said Mr Pandit.

'But the government must ensure that, when they do come into contact with the outside world, the Sentinelese won't be uprooted or hurt. The question is: how?'

(Photograph omitted)