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Scientists exploring a cathedral-sized cave on a remote Indonesian island have discovered a new species of miniature humans that lived 12,000 years ago, leading them to the tantalizing conclusion that other species of humans — dead or alive, big or small — could still be hiding on Earth.

"We anticipate further discoveries of highly endemic, hominin species in locations similarly affected by long-term genetic isolation . . .," the authors, led by Peter Brown, an Australian paleoanthropologist at the University of New England in New South Wales, Australia, write in the paper published today in the science journal Nature.

The new species, dubbed Homo floresiensis after the island of Flores on which it was found, stood only one-metre high fully grown and had a brain the size of a grapefruit.

The shape of its body — and the fact that parts of seven individuals who lived thousands of years apart were found — means that it is not just an anomaly who happened to be short. Nor is the most complete skeleton — likely a female who lived 18,000 years ago — a child, because the skull is solid and the teeth worn.

Researchers have come to the conclusion that it is the descendant of Homo erectus, an early species of primitive human believed to have originated in Africa.

The theory is that Homo erectus reached the Indonesian island of Java millions of years ago and then made it by primitive boat 500 kilometres across the water to the island of Flores. Once there, perhaps a few hundred thousand years ago, that population evolved into a separate species. Evolutionary advantage somehow dictated that they be small, just like the primitive (now extinct) mini-elephants they hunted and ate.

A well documented biological phenomenon is that island populations, isolated for a long time, tend to become either gigantic or miniaturized, leading, for example to the pygmy hippopotamus of Madagascar and the massive flightless moa birds of New Zealand, all now extinct.

The finding has a deep psychological resonance for humans, several of the scientists noted. It plugs into myths about magical little creatures such as elves and leprechauns.

More intriguing still is that long before the Flores crew found the new species, they had been told by local residents of a strange little people who lived there in caves, said Henry Gee, a paleontologist and a senior editor of Nature.

Locals could describe them in detail, including their habits and which caves they were associated with. Locals spoke of sightings as recently as when the Dutch took over the island, less than two centuries ago.

The Flores find has become a sensation in scientific circles, with several top academics saying it is the key find of the past 50 years and that it would cause the rewriting of anthropological textbooks.

Dr. Gee said rumours of the find had been circulating for months, and when the paper arrived at Nature's offices in London in March, he simply gaped.

"I sent it to a lot of people because it's literally unbelievable," he said, adding that Prof. Brown told him he would have been less surprised to have found an alien than a new species of human.

Chris Stringer, a paleoanthropologist who is head of human origins at the Natural History Museum in London, said Prof. Brown sent him a photograph of the skeleton with the cryptic question: "What do you think this is?"

Everyone, including Dr. Stringer, assumed the skeletal remains were millions of years old, whether human or not. They were so convinced that they sent some pieces of charcoal from the find without explanation to Michael Bird, a geochemist at the University of St. Andrews in Fife, Scotland, who had developed a new way of dating extremely old materials using radiocarbon.

He found that the charcoal was a paltry 18,000 years old. Other tests confirmed this, and some samples from the site are only 12,000 years old, just before a volcano blanketed the island with its eruptions, meaning the Homo floresiensis was alive as late as that.

For the past several decades, humans have developed the idea that the progression from ape-like ancestors to modern humans was a long, inexorable, orderly march, culminating in the rule of Homo sapiens as the only human for millions of years, Dr. Gee said.

The Flores find doesn't match that theory at all, he said. It shows that a totally separate human species existed at the same time as modern humans were starting to cultivate the fertile crescent of the Middle East and develop cities, democracy and writing.

"We have tended to think of ourselves as a species very much apart, to whom manifest destiny is accrued," said Dr. Gee. "It's not so."

Dr. Stringer said the find is "humbling."

"The fact that we are the only surviving human species means that we've been lucky," said Dr. Stringer. "We have to make sure we don't die out like all the others did."