University Park, Pa. (10 July 1997)
New evidence from mitochondrial DNA analyses indicates that the Neanderthal
hominid was not related to human ancestors. DNA Knocks Neanderthals out of Human Family Tree
Submitted by: CNN
July 11, 1997
Web posted at: 10:36 a.m. EDT (1436 GMT)
LONDON (AP) -- DNA from a Neanderthal skeleton is giving powerful backing to the theory that all humanity descended from an "African Eve" about 100,000 to 200,000 years ago -- and that Neanderthals were an evolutionary dead end.
Genetic differences indicate the Neanderthals were a different species than the early humans who swept them aside in Europe and western Asia -- although they appear to have split from a common ancestor a half-million years ago, according to German and U.S. scientists.
The DNA test "clearly lends support to this idea about our ancestry: that we have all come out of Africa quite recently in history," said Svante Paabo, who worked on the research at the Zoological Institute at the University of Munich.
Critics of that theory say the argument will rage on, and they await the results of many more DNA tests.
"It is a brilliant, innovative piece of work. I just doubt that it can be faulted on technical grounds," Milford H. Wolpoff, professor of anthropology at the University of Michigan. But he says the researchers have drawn hasty conclusions.
The findings were published in Cell, a journal based in Cambridge, Massachusetts, and outlined Thursday at a news conference in London. Paabo said his results were independently confirmed at Pennsylvania State University.
The Munich team took a small sample -- 0.4 grams -- from the upper arm bone of a skeleton found in 1857 in the Neander Valley near Duesseldorf -- the first Neanderthal skeleton ever found.
Comparing 378 base pairs of the Neanderthal's mitochondrial DNA to that of modern humans, the researchers found an average of 27 differences between modern and Neanderthal DNA -- far more than the typical variation of eight among modern humans.
Mitochondria, the structures within human cells that help produce energy, have their own genes. These genes are passed down the female line with only the occasional mutation.
Paabo cautioned that the study of more Neanderthal DNA samples might turn up some mixing, and thus confirm the possibility of some interbreeding between Neanderthals and our Cro-Magnon ancestors.
Even if Neanderthals were not our ancestors, they were tantalizingly similar. They walked erect, used tools and there is evidence that they coexisted and learned some skills from Cro-Magnon people.
One striking difference is that Neanderthals were bigger than modern humans and had larger brains.
"Any superiority that modern humans had was probably a very slight one at the time and that's why it took so long for the Neanderthals to be replaced," said Chris Stringer, a researcher at London's Natural History Museum.
"Of course this is only one specimen ... but it fits so very well with the view of one side of the argument about Neanderthals -- that they are very distinct, that they are not our ancestor -- that I think it goes a very long way toward resolving the Neanderthal problem," Stringer said.
Wolpoff, the University of Michigan anthropology professor, argued that the fact that a trait or gene sequence seen in ancient people is absent from moderns doesn't mean that one is not the ancestor of the other. The trait could simply have disappeared over time.
If there is a uniform difference between Neanderthal and modern DNA, he added, that may be because widespread mingling of populations has produced uniformity now. And, he added, a divergence in mitochondrial DNA does not necessarily mean a divergence of species.
"What they should be saying is that the argument has just begun," Wolpoff said.
NEANDERTHAL: NO RELATION
By Sean Henahan, Access Excellence
University Park, Pa. (10 July 1997)
New evidence from mitochondrial DNA analyses indicates that the Neanderthal
hominid was not related to human ancestors.
Using refined and expensive genetic techniques, U.S. and German researchers extracted mitochondrial DNA from Neanderthal bone. These studies showed that the Neanderthal DNA sequence falls outside the normal variation of modern humans.
"These results indicate that Neandertals did not contribute mitochondrial DNA to modern humans," says Dr. Mark Stoneking, associate professor of anthropology at Penn State. "Neandertals are not our ancestors."
The findings will cause of reconsideration of the current consensus
that Neandertals became extinct only 30,000 years ago and co- existed for some time with
modern humans in Europe. The new research indicated that Neandertals and modern
humans diverged genetically 500,000 to 600,000 years ago. While the two species may have
lived at the same time, Neandertals did not contribute genetic material to modern humans,
the researchers report.
The team analyzed bone from a Neanderthal specimen found in the eponymous valley. This is
the first time researchers have been able to extract useful DNA fragments from such a
specimen.
"The ability to extract DNA from ancient bone is dependent on many factors, including preservation, temperature and humidity," says Stoneking, a faculty member in Penn State's College of the Liberal Arts.
The researchers devised an innovative technique using overlapping short strands of DNA to obtain a mitochondrial DNA sequence of 378 base pairs. The researchers ran multiple extractions and amplifications. to ensure that errors caused by damaged DNA were not incorporated into the sequence and that modern human DNA did not contaminate the samples. At the same time the researchers ran a parallel extraction and amplification of the DNA.
To begin amplification, the researchers used two human primers -- small pieces of DNA that match the beginning of the sequence to be amplified.
"The first two human primers we chose worked," says Stoneking. "It turns out this was a lucky choice."
To check that the amplified DNA was really Neanderthal, the researchers prepared primers based on their extracted sample and ran them on numerous human DNA samples.
"The Neandertals primers did not amplify any human DNA," says Stoneking. "Most human primers would probably not work on Neanderthal DNA."
The researchers compared the Neanderthal sequence with 2,051 human sequences and 59 common chimpanzee sequences. They found that the differences in Neanderthal DNA occurred at sites where differences usually occur in both humans and chimps.
"The changes reflect the evolutionary pattern typical of mitochondrial DNA sequences of living humans and chimpanzees, not that of random damage or degradation," says Stoneking.
When the researchers looked at the Neanderthal sequence with respect to 994 human mitochondrial DNA lineages including Africans, Europeans, Asians, Native Americans, Australians and Pacific Islanders, they found the number of base pair differences between the Neanderthal sequence and these groups was 27 or 28 for all groups.
"While Neandertals inhabited the same geographic region as contemporary Europeans, the observed differences between the Neanderthal sequence and modern Europeans do not indicate a closer relationship to modern Europeans than to other contemporary human populations," says Stoneking.
The researchers used phylogenetic tree reconstruction -- a method that uses mitochondrial DNA to place individual groups in relative relationship -- to check the results of their pair- wise DNA comparisons. The trees show that the Neanderthal sequence branches before the divergence of the various human mitochondrial DNA lineages, but after the split from chimpanzees.
This phylogenetic tree also shows that the first three branches of humans are of African origin, with only the fourth branch showing non-African sequences.
"The branching pattern indicates that the ancestor of the mitochondrial DNA gene pool of contemporary humans lived in Africa," says Stoneking of Penn State.
"I really looked for holes in the methodology, but I just couldn't find any. It seems to be an authentic sequence and certainly as far as I can tell the most rigorous ancient DNA study I've ever seen," says evolutionary biologist and ancient DNA researcher Blair Hedges of Penn State.
The researchers caution that the current results are derived from only one individual and note that DNA may be difficult to extract from other specimens. Even if theNeanderthals did not contribute mitochondrial DNA to modern humans, it is still possible that they contributed other genes, they emphasize.
The research appears in the June 11, 1997 issue of Cell.