Thursday, March 25, 2010

New Ancient Human

Nicholas Wade:
Researchers extracted DNA from a 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 tiny fragment of bone from a fifth finger was excavated by Russian archaeologists working at Denisova Cave in southern Siberia's Altai Mountains in 2008.

The researchers, led by Johannes Krause and Svante Paabo of the 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.

“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.”
-Dr. Paabo, a pioneer in decoding ancient human 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 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.

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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