Test of Neanderthal DNA Finds No Link to Humans
The stocky big-game hunters known as Neanderthals who lived during the last Ice Age did not evolve into modern humans, nor did the two groups intermarry and have surviving children--even though they apparently roamed prehistoric Europe and Asia together for thousands of years, an international research team reported Thursday.
In a landmark study, researchers in the United States and Germany said they succeeded for the first time in extracting, reproducing and analyzing maternal DNA from a pulverized piece of 100,000-year-old Neanderthal bone.
By comparing those ancient genes with genetic material from hundreds of people around the world today, they discovered that Neanderthals did not contribute any maternal DNA to modern humanity. This strongly suggests that the species was an evolutionary dead end, edged out--or killed off--by the forebears of contemporary Homo sapiens.
Svante Paabo, the University of Munich genetics expert who led the six-year effort, said, “This is the first genetic information we have from Neanderthals, and it gives no indication that any mixing between the two groups would have taken place.”
The fate of these primitive people--who buried their dead with flowers and may have been the first to feel religious stirrings--is one of the most hotly disputed questions in the study of human beginnings. Each new fossil find triggers debate about their role in the evolution of modern humankind.
The finding that Neanderthals are a genetically distinct species also serves to buttress a controversial new picture of the time in which modern human beings evolved. It now seems that three separate human species--Neanderthals, anatomically modern humans and an older species called Homo erectus--apparently co-existed until as recently as 30,000 years ago in parts of Europe and Asia.
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Although the place of Neanderthals in the human family tree has remained uncertain, their scientific image has evolved dramatically: from the bestial, stooped subhuman creatures envisioned by the 19th century scientists who first discovered their bones to the relatively sophisticated tool-users now recognized by modern anthropologists.
Evidence even indicates that Neanderthals traded tools and jewelry with Cro-Magnon people, who became modern humans. Many experts, however, believe that is as far as the relationship went and that Neanderthals became extinct 30,000 years ago. For many, this newest finding, published today in the journal Cell, appears to settle the matter.
For their study, the researchers extracted less than one-hundredth of an ounce from the upper arm bone of the first Neanderthal skeleton ever found--a set of fossil remains discovered 140 years ago in the Neander Valley of Germany.
From that, they were able to isolate no more than 1,500 maternal DNA molecules from the energy-producing bodies inside the cells called mitochondria. The scientists then multiplied the molecules for analysis. The genes in the mitochondria are passed down the female line with only occasional changes.
The results showed that humans and Neanderthals last shared a common ancestor--most likely Homo erectus--about 600,000 years ago and offered strong support for the idea that modern humanity emerged from Africa about 100,000 years ago.
Several experts called the new research a tour de force investigation of ancient DNA.
“The present recovery of Neanderthal DNA represents a landmark discovery, which is arguably the greatest achievement so far in the field of ancient DNA research,” said Tomas Lindahl, a genetics expert at the Imperial Cancer Research Fund in England who reviewed the research for Cell.
The evidence is “compelling and convincing,” he said.
Even those who dispute the study’s conclusions about human ancestry--believing that Neanderthals, with their large brains and muscular frames, indeed evolved into modern human stock--still hailed the technical achievement involved in recovering the DNA from the fossil as “astonishing.”
C. Loring Brace, curator of biological anthropology at the University of Michigan’s Museum of Anthropology, has made a life’s study of the fossil Neanderthal remains. His meticulous examination of the bones and fossil teeth long ago convinced him that Neanderthals evolved into modern human stock.
The new DNA evidence, while impressive, is not enough to warrant any conclusions about the ancestral relationship between humans and Neanderthals, he said. Genetic tests of other Neanderthal remains are necessary, he said.
“I think it is fascinating. It is quite different from anything living now. [But] it is only one specimen, and it is unrealistic to make any conclusion,” he said. “Our ability to make coherent biological sense of all this still is in its infancy.”
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Indeed, much research into ancient DNA--whether it involves genetic material purportedly from dinosaurs, prehistoric leaves or 100-million-year-old insects trapped in amber--has been riddled with false results and technical uncertainty.
Paabo and his colleagues acknowledged the enormous difficulties in analyzing ancient DNA without contaminating it with modern material and said they had taken extraordinary precautionsk. To ensure the integrity of their results, the entire experiment was reproduced independently by a laboratory at Pennsylvania State University.
“We have performed all controls that we can possibly think of,” Paabo said.
The precautions appear to have reassured many scientists. “I have not encountered anyone in the scientific world who doubts that they have recovered Neanderthal DNA,” said Chris Stringer, an expert in early humans at London’s Natural History Museum.
