[xmca] Bone May Reveal a New Human Group

["Peter Smagorinsky" <smago@uga.edu>]

Another new evolutionary find, especially dramatic as the Texas curriculum
committee, populated by people who genuinely believe that humans and
dinosaurs co-habited the earth 5,000 years ago following Creation, is
presenting its own version of history.

 


Bone May Reveal a New Human Group


By NICHOLAS WADE
<http://topics.nytimes.com/top/reference/timestopics/people/w/nicholas_wade/
index.html?inline=nyt-per> 


Published: March 24, 2010


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A previously unknown kind of human group vanished from the world so
completely that it has left behind the merest wisp of evidence that it ever
existed - a single bone from the little finger of a child, buried in a cave
in the Altai mountains of southern Siberia. 


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Researchers extracted DNA from the bone and reported Wednesday that it
differed conspicuously from that of both modern humans and of Neanderthals,
the archaic human species that inhabited Europe until the arrival of modern
humans on the continent some 44,000 years ago. 

The child who carried the DNA lineage was probably 5 to 7 years old, but it
is not yet known if it was a boy or a girl. The finger bone was excavated by
Russian archaeologists in 2008 from a place known as the Denisova cave. 

The researchers, led by Johannes Krause and Svante Paabo of the
<http://www.eva.mpg.de/english/index.htm> Max Planck Institute for
Evolutionary Anthropology in Leipzig, Germany, are careful not to call the
Denisova child a new human species, though it may prove to be so, because
the evidence is preliminary. 

But they say the genetic material extracted from the bone, an element called
mitochondrial DNA, belonged to a distinct human lineage that migrated out of
Africa at a different time from the two known archaic human species. Homo
erectus, found in East Asia, left Africa two million years ago, and the
ancestor of Neanderthals emigrated some 500,000 years ago. The number of
differences found in the child's DNA indicate that its ancestors left Africa
about one million years ago, the researchers say. Their report is published
online in the journal Nature. 

Dr. Paabo, a pioneer in decoding ancient human DNA, said at a news
conference that before asserting that the Denisova child was a new species,
he needed to rule out the possibility that it belonged to a population
formed by interbreeding between the new lineage and a known species. He said
he was analyzing the rest of the child's DNA, from the main or nuclear
genome, to test this possibility. 

"Back at the time this lineage came out of Africa, it had to have been a
distinct group, perhaps a distinct species," he said. "But whether or not
this individual was a distinct species, we have to wait for the nuclear
DNA." 

The finger bone was found in a layer laid down on the cave floor between
48,000 and 30,000 years ago, according to radiocarbon dating. At that time,
toward the end of the Pleistocene Ice Age, which ended 10,000 years ago, the
climate was probably much colder. The people of the new lineage presumably
wore clothes, Dr. Krause said, because chimpanzees and gorillas cannot
withstand much cold, suggesting that fur alone is inadequate protection. 

The artifacts found in the cave in the same layer as the finger bone include
ornaments and a bracelet that are typical of modern human sites from the
Upper Paleolithic age in Europe. These are puzzling artifacts to be found
with a nonmodern human species. But bones can move up and down in
archaeological sites, and it is hard to know if the finger bone is truly
associated with these artifacts, Dr. Krause said, even though there is
little sign of mixing in the cave's layers. 

The valley beneath the Denisova cave 30,000 years ago would have been mostly
a steppe, or treeless grassland, according to pollen analysis, and it was
roamed by ice-age species like the woolly mammoth and woolly rhino, Dr.
Krause said. 

The region was inhabited by both Neanderthals and modern humans at that
time. Counting the new human lineage, three human species may have lived
together in proximity. "So the picture of the humans around in the late
Pleistocene gets a lot more complex and a lot more interesting," Dr. Paabo
said. 

The standard view has long been that there were three human migrations out
of Africa - those of Homo erectus; of the ancestor of Neanderthals; and
finally, some 50,000 years ago, of modern humans. But in 2004,
archaeologists reported that they had found the bones of miniature humans
who lived on the Indonesian island of Flores until 13,000 years ago, posing
a serious problem for this view. The new lineage is the second such
challenge, and it suggests that human migrations out of Africa, though far
from continuous, were more frequent than supposed. 

"We are learning more and more what a luxuriant evolutionary tree humans
have had," said Ian Tattersall, a paleoanthropologist at the
<http://topics.nytimes.com/top/reference/timestopics/organizations/a/america
n_museum_of_natural_history/index.html?inline=nyt-org> American Museum of
Natural History in New York. The tree during evolutionary time has kept
sprouting new branches, all but one of which die off, before the process is
repeated. 

As recently as 30,000 years ago, it now appears, there were five human
species in the world: Homo erectus, the little Floresians, Neanderthals,
modern humans and the new lineage from the Denisova cave. This is similar to
the situation two million years ago, when four hominid species are known to
have lived in the Turkana Basin of Kenya, Dr. Tattersall said. 

"We think it's normal to be alone in the world as we are today," Dr.
Tattersall said, and to see human evolution as a long trend leading to Homo
sapiens. In fact, the tree has kept generating new branches that get cut
off, presumably by the sole survivor. "The fossil record is very eloquent
about this, and it's telling us we are an insuperable competitor," Dr.
Tattersall said. Modern humans' edge over other species probably emerged
from their ability to process information: "We can invent alternatives in
our heads instead of accepting nature as it is," Dr. Tattersall said. 

If the nuclear DNA of the Denisova child should differ as much as its
mitochondrial DNA does from that of Neanderthals and modern humans, the case
for declaring it a new species would be strengthened. But it would be
unusual, if not unprecedented, for a new species to be recognized on the
basis of DNA alone. 

In new excavations starting this summer, archaeologists will look for
remains more diagnostic than the finger bone. Researchers will also begin
re-examining the fossil collections in museums to see if any wrongly
assigned bones might belong instead to the new lineage, Dr. Krause said.

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