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10 July 1997 7:00 pm
MUNICH, GERMANY--A stunning, first-ever analysis of DNA from a Neandertal bone supports the view that Neandertals were an evolutionary dead end rather than our ancestors and gives a major boost to the field of ancient DNA. Scientists in Germany and the United States report in today's issue of Cell that the DNA data lend a new kind of support to the now-favored view that Neandertals were a side branch of the human family tree.
Researchers familiar with the new work are convinced that this Neandertal sequence is the real thing. It's "the most rigorous ancient DNA study I've ever seen," says evolutionary biologist and ancient DNA researcher Blair Hedges of Pennsylvania State University.
The international team had to overcome vast difficulties to get their results. DNA begins to degrade from the moment of death, and in most cases all is probably gone after 50,000 to 100,000 years. It's also tough to tell ancient human DNA from the modern DNA that so often contaminates a sample. But Matthias Krings and Svante Pääbo OF the University of Munich and Anne Stone and Mark Stoneking of Pennsylvania State University succeeded with a sample from the upper arm bone of the prototype Neandertal skeleton, discovered in Germany in 1856.
Krings used a number of careful--and expensive--laboratory techniques to guard against contamination and extract his sample. With the polymerase chain reaction, he amplified part of a particular sequence called the control region in the DNA of mitochondria, cellular organelles that have their own tiny genome and are inherited only from the mother.
The team found mutations in stretches of the DNA that never vary among modern humans, which pegged the DNA as ancient. When they compared the Neandertal sequence with 986 distinct sequences from living humans, they found that the ancient DNA was three times more different than modern human sequences. That puts the Neandertal sequence outside the statistical range of modern human variation and, says Pääbo, makes it "highly unlikely that Neandertals contributed to the human mtDNA pool."
In fact, it suggests a deeply rooted split in the human family tree, says paleoanthropologist Christopher Stringer of The Natural History Museum in London. The finding implies that the two lineages diverged before the first known Neandertal at about 300,000 years ago, and long before the first modern humans at less than 200,000 years ago. That, he says, supports the "Out of Africa" hypothesis--that modern humans arose recently in Africa and then replaced existing human populations around the world, including the European Neandertals, without interbreeding with them.
Others, such as paleoanthropologist Milford Wolpoff of the University of Michigan, Ann Arbor, aren't convinced that DNA from one individual settles the long-standing debate over modern human origins. But most anthropologists are thrilled to see that recovering ancient human DNA is feasible. Says paleoanthropologist Dan Lieberman of Rutgers University, "The fact that they managed to find DNA from a region of prime importance is proof that there is a God who likes paleoanthropology."
For more details, Science Online subscribers can link to the full text of the Research News story.