THREE HUMAN SPECIES COEXISTED ON EARTH, RESEARCHERS CONTEND.

Byline: John Noble Wilford The New York Times

Scientists have found stunning new data showing that a third human species apparently coexisted on Earth with two others as recently as 30,000 years ago.

In research that could redraw the human family tree and is certain to be controversial, the scientists re-examined two major fossil sites along the Solo River in Java and found that an early human relative, Homo erectus, appeared to have lived there until about 27,000 to 53,000 years ago.

Writing in today's issue of the journal Science, the scientists said the new dates were ``surprisingly young and, if proven correct, imply that Homo erectus persisted much longer in Southeast Asia than elsewhere in the world.''

Confirmation of the new dates would mean that at least in Java, this archaic species, which evolved 1.8 million years ago, survived some 250,000 years longer than scientists have believed. This surviving population of Homo erectus in Indonesia would have been alive at the same time as anatomically modern humans - Homo sapiens - and also Neanderthals, whose exact place in human evolution is the subject of endless debate.

The Neanderthals, who lived in Europe and western Asia for some 300,000 years, appear to have made their last stand 30,000 years ago in southern Spain. By then, modern Homo sapiens, who are widely thought to have evolved in Africa 200,000 to 100,000 years ago, had spread all over Africa and Eurasia, as far as Australia. It is not known how much contact the three species had or if they could interbreed.

The new findings emphasize the probability that it is uncommon for only a solitary human species to be on Earth. Until a couple of decades ago, scientists conceived of the human lineage as a neat progression of one species to the next and doubted that two species overlapped in place or time.

Another implication of the more recent date for Homo erectus is to undercut a pillar of the multiregional theory for the origin of modern Homo sapiens.

As the most advanced known representatives of Homo erectus, the Java fossils have appeared to be a clear intermediate step in the evolution of Homo erectus in Southeast Asia to the first Australians, who were modern Homo sapiens. This has lent support to the idea that modern humans emerged gradually out of Homo erectus in many parts of the world. The alternative and more favored out-of-Africa theory holds that modern humans evolved in Africa less than 200,000 years ago and displaced Homo erectus as they migrated to the ends of the Earth.

The team of scientists, led by Dr. Carl Swisher III of the Berkeley Geochronology Center in California, concluded that it was ``no longer chronologically plausible'' to argue that the Java Homo erectus evolved into Asian Homo sapiens. From earlier fossil evidence and rock art, Australian Homo sapiens are believed to be at least 30,000 years old and possibly much older.

``The multiregionalists will have to do some fast talking to explain this,'' said Dr. Philip Rightmire, a paleoanthropologist at the State University of New York at Binghamton. ``It's quite a blow for them to absorb, but neither side has won the day yet in this theoretical battle.''

Dr. Milford Wolpoff, a paleoanthropologist at the University of Michigan and an outspoken leader of the multiregional theorists, questioned both the accuracy of the dates and the identification of the skulls at the Java sites. Contending the skulls are Homo sapiens and not Homo erectus, Wolpoff said these questions should have been answered more convincingly before the team published its report.

Wolpoff has studied the skulls at one of the two Solo River sites and compared them with early Australian Homo sapiens. He said an ancestral ``link between them is incontrovertible.''

In an accompanying article in Science, Dr. Alan Thorne of the Australian National University in Canberra, one of Wolpoff's allies, said, ``There is a great long list of characters that are the same in the Solo skulls and the earliest known human people from Australia.''

Even if the Java fossils are indeed relatively young, Thorne added, they look so much like the Australian fossils that the two species may have shared a recent ancestor.

Both Rightmire, an authority on Homo erectus, and Dr. Susan Anton, a paleoanthropologist at the University of Florida who was a member of Swisher's team, said they were satisfied that the Java specimens are Homo erectus, though the skulls show signs of having evolved a somewhat larger brain than earlier members of the species. The fact that Homo erectus and Homo sapiens now appear to have overlapped, Anton said, ``raises the possibility of gene flow between the two lines.''

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Chart/3 Photos

Chart/Photo: Skulls found in Java suggest that Homo erectus, thought to have died out hundreds of thousands of years ago, walked the earth at the same time as modern Homo sapiens.

The New York Times