There’s no sign of Neanderthals lurking in our family tree, researchers declare, saying that DNA from a Neanderthal skeleton is helping resolve one of the great debates of human evolution.
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.
Their finding gives 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.
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 Svanto 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’s a fantastic achievement,” said Christopher Stringer of the Natural History Museum in London, the leading proponent of the out-of-Africa theory. “In terms of our knowledge of human origins, it’s as big as the Mars landing.”
Even Milford Wolpoff of the University of Michigan, the most forceful advocate of the rival, gradual-evolution-everywhere theory known as multi-regionalism, called the results “exciting.” The analysis relies on a recently developed and somewhat controversial method of measuring genetic difference. “But if anybody could do this beyond criticism,” Wolpoff said, “it’s Svante Paabo and his laboratory” at the University of Munich.
“It is a brilliant, innovative piece of work. I just doubt that it can be faulted on technical grounds,” Wolpoff said. But he says the researchers have drawn hasty conclusions.
The findings were published in Cell, a journal based in Cambridge, Mass., 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. The difference is drastic - about half as much as today’s humans differ from chimps. Disparities that large, the researchers conclude, suggest that Neanderthals diverged about 600,000 years ago from the line that eventually would become today’s Homo sapiens.
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 time and that’s why it took so long for the Neanderthals to be replaced,” Stringer said.
“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.