3 HUMAN SPECIES CO-EXISTED ON EARTH
Thu, 12 Dec 1996 23:59:00 -0500
Source: DAVID TILBURY
By JOHN NOBLE WILFORD
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 Friday's issue of the journal Science, the scientists said the
new dates were "surprisingly young and, if proven correct, imply that H.
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 after it was thought to have become extinct. This surviving population
of H. 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 H. 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.
In any case, specialists in human evolution noted, the new findings
suggest that the present phenomenon of a solitary human species on earth may
be more the exception than the rule. Until about a couple of decades ago,
scientists conceived of the human lineage as a neat progression of one
species to the next and generally thought it impossible that two species
could have overlapped in place or time.
Another implication of the more recent date for H. erectus is to undercut
a pillar of the multiregional theory for the origin of modern H. sapiens.
As the most advanced known representatives of H. erectus, the Java fossils
have appeared to be a clear intermediate step in the evolution of H. erectus
in Southeast Asia to the first Australians, who were modern H. sapiens. This
has lent support to the idea that modern humans emerged gradually out of H.
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 H. 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 H. erectus evolved into
Asian H. sapiens. From earlier fossil evidence, Australian H. sapiens are at
least 30,000 years old, and could be much older, judging by rock art.
"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
who is 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 that they were H. sapiens and not H. erectus. Wolpoff said
these questions should have been answered more convincingly before the team
published its report.
As one who has studied the skulls at Ngandong, one of the two sites, and
compared them with early Australian H. sapiens, Wolpoff said the idea of 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 H. 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 were H.
erectus, though the skulls did show signs of their having evolved a somewhat
larger brain than earlier members of the species. The fact that H. erectus
and H. sapiens now appear to have overlapped, Dr. Anton said, "raises the
possibility of gene flow between the two lines."
The Java fossils were discovered in the 1930s by Dutch geologists. Over
the years, various efforts to date the specimens have yielded ages of as high
as 300,000 and 250,000 years and, recently, as low as 100,000 years.
The most reliable means of dating such ancient material is to determine
the age of volcanic ash in the sediments, but none is associated with the
Solo specimens. Similarly, a number of other techniques were not suitable,
and the skulls themselves could not be dated because they would have been
damaged.
Swisher explained in an interview that he had dug a test trench at the
Ngandong site, on a terrace at the bend in the Solo River. He noted that the
layer of sediment where the skulls had been found also contained teeth of
water buffalo. The teeth were analyzed through two techniques for measuring
the radioactive decay of uranium that the teeth had absorbed from the soil.
This indicated how long the teeth had been buried.
To assure themselves that they were sampling the same sediment layer where
the H. erectus skulls had been excavated, the scientists said, they compared
and dated similar water buffalo teeth collected by the Dutch geologists at
the time of the original discoveries. The specimens are housed at Gadjah Mada
University in Yogyakarta, Indonesia. The dating analysis was conducted at
McMaster University in Hamilton, Ontario.
Some scientists said they were still concerned that erosion and river
currents could have mixed up older H. erectus skulls with younger water
buffalo teeth, but Swisher said this was unlikely to have occurred in the
same way for 12 different skulls at two widely separated sites.
If the dates are right, as Swisher's team noted at the conclusion of its
report, "the temporal and spatial overlap between H. erectus and H. sapiens
in Southeast Asia is reminiscent of the overlap of Neanderthals (H.
neanderthalensis) and anatomically modern humans in Europe."
Other Places of Interest on the Web
Early Human Species May Have Coexisted With Our Own , from ScienceNOW
http://www.sciencenow.org
/html/961212a.htm
Copyright 1996 The New York Times
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