Neandertal Gene Study Reveals Early Split With Humans
for National Geographic News
|October 26, 2006|
A new genetic study bolsters theories of an early human-Neandertal split and is helping scientists pinpoint what makes humans unique.
Controversy has long swirled in the scientific community over how closely the Eurasian hunters resembled modern humans, with some researchers even claiming Neandertals (often spelled Neanderthals) were actually members of our own species, Homo sapiens. (Related: "Neandertals' Last Stand Was in Gibraltar, Study Suggests" [September 13, 2006].)
A new study by geneticist James Noonan at Lawrence Berkeley National Laboratory, however, reveals that modern humans and Neandertals' most recent common ancestor probably perished about 400,000 years ago.
The research was presented earlier this month at the American Society of Human Genetics conference in New Orleans, Louisiana (get a genetics overview).
Richard Potts, director of the human origins program at the National Museum of Natural History in Washington, D.C., called Noonan's work "highly significant."
"Each part of the Neandertal genome is an archive of the similarity and distinction [between Neandertals and] all people living today," he said. "Comparison to a lineage in our own family tree helps us understand which elements of the genetic code make us human."
To obtain the raw material for his study, Noonan extracted DNA from fossilized Neandertal bones.
Combing the samples for Neandertal-specific genetic sequences was a painstaking process bogged down by large amounts of contamination.
"Most of the DNA we got was bacterial DNA from organisms that had colonized the specimens," Noonan said. "We can pick out the ancient DNA sequences because they're shorter and more degraded."
After analyzing the genetic content of the sequences, Noonan and his colleagues began cataloging them in a library similar to that used to help organize the human genome.
Initial results indicate Neandertals have contributed surprisingly little to modern humans' genetic makeup.
Noonan's work represents a significant advance over earlier studies of Neandertal genetics, such as those conducted by William Goodwin of the University of Glasgow in Scotland. (Related: "Neandertals Not Our Ancestors, DNA Study Suggests" [May 14, 2003].)
That early work involved analysis of mitochondrial DNA, which tends to stay preserved longer than DNA found inside the nuclei of cells. But Noonan analyzed nuclear DNA, which holds a much greater wealth of information.
"Nuclear DNA is where all the biology is," Noonan said. "We want to understand how traits like language and cognition are encoded, and none of those traits can be found in mitochondrial DNA."
Race to the Finish
Like the multiple groups who worked simultaneously to sequence the human genome, Noonan faces competition from other inspired teams.
Genetic anthropologist Svante Paabo of the Max Planck Institute in Leipzig, Germany, is working on a similar sequencing project using DNA from bone specimens belonging to a Neandertal who lived in Croatia about 45,000 years ago.
"A Neandertal genome sequence will provide a catalog of all changes that happened in the human genome after humans separated from Neandertals, so it will be a wonderful tool for scientists who want to find out what makes modern humans unique," Paabo said.
While Noonan's focus is on studying the sequences of Neandertal DNA he considers most significant—those he can compare to modern human DNA sequences—Paabo's goal is to sequence the entire Neandertal genome within two years.
Based on his results to date, Paabo expects to see some surprises as his project proceeds.
"Neandertal DNA is degraded in specific ways that we had not anticipated, and in some ways Neandertals actually look closer to humans than we had expected," he said.
The Natural History Museum's Potts hopes Noonan's and Paabo's investigations, in addition to fleshing out Neandertals' genetic profile, will lend insight into their day-to-day existence, including the challenges they faced that shaped specific genetic adaptations.
"The genetic analysis of Neandertals complements the study of fossils and the archaeological record of Neandertal behavior," he said.
"All this evidence allows us to understand exactly how Neandertals lived and adapted to a changing world that eventually included our species."
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