Scientists have discovered a tiny species of ancient human that lived 18,000 years ago on an isolated island east of the Java Sea -- a prehistoric hunter in a "lost world" of giant lizards and miniature elephants.
These "little people" stood about three feet tall and had heads the size of grapefruit. They coexisted with modern humans for thousands of years yet appear to be more closely akin to a long-extinct human ancestor.
Researchers suspect the earlier ancestor may have migrated to the island and evolved into a smaller dwarf species as it adapted to the island's limited resources. This phenomenon, which scientists have come to call the "island rule," is common in the animal world but had never been seen in human evolution.
"Not even in primates," said paleoanthropologist Peter Brown, of Australia's University of New England, a member of the multinational team reporting on the find today in the journal Nature. "But even though we have evidence of intelligence [in the new species], they were clearly subject to isolation and dwarfing."
Colleagues marveled at the find as an evolutionary aberration -- an archaic human that survived to a time when Neanderthals -- which had been thought to be the last pre-modern species to share the planet with modern humans -- had probably been extinct for more than 10,000 years.
"This is a great fossil find that speaks mounds about evolutionary experiments and the variation they caused," said paleoanthropologist Ken Mowbray, of the American Museum of Natural History. "We have to step back and reevaluate everything we have. It's really cool."
The research team discovered the new species in a limestone cave on Flores Island, in the Indonesian archipelago east of Java. They described the remains -- a fairly complete skull, the jawbone and much of the skeleton -- as those of a 30-year-old woman. The team named her Homo floresiensis.
The team also found a tooth and a few bones from two other skeletons, and Brown said subsequent excavations had brought the team the remains of between five and seven people in all. "They're all tiny," Brown said in a telephone interview from Australia. "No big people."
The new find is certain to influence a flourishing debate over the human presence both in Indonesia and on Flores, which lies immediately east of the so-called Wallace Line dividing islands that were once connected to Australia or Asia, and those, such as Flores, that have been surrounded by water for the last 2.6 million years.
Generally speaking, islands west of the Wallace Line, such as Java, display a full range of mainland animals. On the isolated, ecologically limited eastern islands, however, animals often evolved in conformity with the island rule: those smaller than rabbits got larger; those larger than rabbits got smaller.
Flores, with a limited food supply and no predators, was a prime example of this mechanism. At the time the Flores woman lived, the island was host to both Komodo dragons three feet long and a dwarf variation of stegodon, a prehistoric elephant.
In 1998, Flores project leader Michael J. Morwood, a University of New England archaeologist, reported discovering stone tools on Flores that were 840,000 years old, a controversial find that did not immediately win broad acceptance. That site had no human remains.
Even more controversial is a dispute over bones found in Java. Some scientists say they are 300,000 years old, but others date them as recently as 27,000 years ago. The later date now "seems more plausible" in light of the new discovery, said Rick Potts, director of the Smithsonian Institution's Human Origins program, because Flores's little people may be an evolutionary offshoot of the earlier species.
These earlier human ancestors, known as Homo erectus, arose in Africa about 2 million years ago and spread throughout Eurasia, beginning a bit less than 1 million years ago. Despite the disputed 27,000-year-old date of the Java find, the preponderance of evidence suggests that Homo erectus went extinct perhaps 200,000 years ago. Modern humans arose in Africa about 150,000 years ago, reaching Australia and Indonesia around 50,000 years ago.
The Flores woman has virtually nothing in common with modern humans, and while some traits -- such as her small stature -- pointed toward other, extremely early species, Brown said she most closely resembles a reduced-size Homo erectus with a grapefruit-size brain -- 23.2 cubic inches.
The most plausible explanation for the small size is that the Flores people, like the animals with whom they lived, succumbed to the island rule. "You had limited availability of food and no predators," Brown said. Short people had a better chance to survive.
The small brain, however, "is a big surprise," Potts said, and a major departure from the general evolutionary trend -- that the human brain grew over time. A full-size Homo erectus had a brain volume between 54.9 and 73.2 cubic inches, while modern human brains can reach 85.4 cubic inches.
Still, the evidence shows that the Flores people were far from stupid. Morwood, in a second Nature article, said the team found stone flakes, points and barbs indicating that the cave's inhabitants hunted young stegodons. These artifacts were found in levels of excavation extending as far back as 95,000 years ago.
"How did they do it? The answer is to not look at brain size," Brown said. "We don't have many more neurons than chimps do, but we use them differently. I think the crucial thing was probably the brain's internal organization."
On the question of how the little people got to Flores Island, the team had no answers. The stegodons "were good swimmers, but the humans couldn't have swum," Brown said. "The popular notion is that they or their ancestors either intentionally or accidentally rafted in."