A century-old question concerning the Neanderthals has been settled, thanks
to new genetic evidence. After extracting DNA from fossil bones, anthropologists
say they are now sure that Neanderthals were not our ancestors, but a side
branch of our family tree that became extinct about 30 000 years ago.
The first Neanderthal bones were discovered in 1856, in a limestone cave in
Germany. Ever since, their role in human prehistory has been controversial.
Heavy-boned and muscular, the Neanderthals have been embraced by some scientists
as forerunners of modern European populations, while others have rejected them
as irrelevant. Over the past few decades, the pendulum has swung in the latter
direction, with Neaderthals judged to be a distinct species.
Nevertheless, as Northern Illinois University anthropologist Fred Smith
observes, 鈥渁mong rank and file physical anthropologists, many were not convinced
that Neanderthals were a separate species鈥�. Smith, who has backed the view that
Neanderthals were ancestral to the first modern humans in Europe, concedes that
the new study is 鈥渢he strongest evidence yet鈥� that Neanderthals were not the
ancestors of modern Europeans.
Advertisement
The evidence comes in the form of a short sequence of mitochondrial DNA, 328
nucleotides long. This was extracted from less than half a gram of fossil bone
from the original Neanderthal specimen. Svante P盲盲bo, a pioneer in
ancient DNA research at the University of Munich, led the effort. He joined
forces with Mark Stoneking at Pennsylvania State University, where the
extraction and analysis were replicated to check the results.
In last week鈥檚 Cell (vol 90, p 19), the team reports that both labs
retrieved the same DNA sequence. The Neanderthal DNA was different in 27 of the
328 positions when compared with an average modern human sample. Within modern
human populations, individuals differ by an average of only eight positions.
鈥淚 don鈥檛 know of any reasonable interpretation of these data, other than that
Neanderthals were not ancestral to modern humans,鈥� says P盲盲bo. 鈥淥f
course, we are talking about a single DNA sequence from a single individual, and
we need to repeat the work on other Neanderthal specimens.鈥�
If confirmed, the data indicate that Neanderthals and modern humans last
shared a common ancestor some 600 000 years ago, an estimate based on the number
of mutations that have accumulated in the DNA.
The results support the 鈥淥ut of Africa鈥� model of modern human evolution. This
holds that the modern human physique first appeared in Africa about 150 000
years ago, and then spread into the rest of the Old World, replacing existing
populations of archaic human forms.
The chief opponent of the 鈥淥ut of Africa鈥� model, Milford Wolpoff of the
University of Michigan, acknowledges that the new genetic work is technically
sound, but disputes the interpretations of the data. 鈥淔or every interpretation
they give, an equally plausible alternative can be offered,鈥� he argues.
鈥淎lternatives can be thought of,鈥� responds P盲盲bo, 鈥渂ut they are by
no means equally plausible.鈥� Chris Stringer of the Natural History Museum in
London adds that the result is 鈥渢he biggest advance in our ability to understand
the role of Neanderthals since the fossils were first discovered鈥�.