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Fri, 27 May 2011 22:13:03 -0400
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Were Neandertals and Modern Humans Just Ships in the
Night?

by Michael Balter
Science Magazine
9 May 2011
http://news.sciencemag.org/sciencenow/2011/05/were-neandertals-and-modern-huma.html

Researchers have long debated how long Neandertals stuck
around after modern humans invaded their home
territories in Europe and Asia around 40,000 years ago.
Some say as long as 10,000 years; others think
Neandertals went extinct almost immediately. A new
radiocarbon dating study of a Neandertal site in Russia
concludes that the latter scenario is most likely, and
that Neandertals and modern humans were probably like
ships in the night. But don't expect this to be the last
word on this contentious subject.

Neandertals and modern humans likely encountered one
another at least twice during prehistory. The first time
was at least 80,000 years ago in the Near East, as
evidenced by findings of both Neandertal and modern
human bones in caves in Israel. But the moderns, who
came up from Africa, apparently did not venture any
farther than the Near East at that time, possibly due to
competition from the Neandertals who were then occupying
much of Europe and Asia.

Then, shortly before 40,000 years ago, Homo sapiens-
possibly now armed with more sophisticated technology
and adaptive skills-began the massive migration that
would take our species to pretty much everywhere on the
globe, including the territories in Europe and Asia that
were already occupied by Neandertals.

Recent genetic studies suggest that Neandertals and
moderns interbred the first time but not the second.
That has led some researchers to suspect that they were
not neighbors for very long during the more recent
overlap, especially in Europe. Some scientists, however,
say that Neandertals hung on in "refugia" like southern
Spain and Gibraltar until as late as 32,000 years ago.
(All dates in this story are in calibrated radiocarbon
years.)

For the past several years, radiocarbon dating expert
Thomas Higham of the University of Oxford in the United
Kingdom has been working with researchers all over
Europe to improve the accuracy of radiocarbon dating at
prehistoric sites. The technique relies on the
radioactive isotope carbon-14, whose radioactivity
diminishes over time in a predictable manner, allowing
researchers to calculate the age of ancient human sites
using charcoal from fires or the bones of the
prehistoric humans themselves. But ancient carbon
sources can easily become contaminated with more recent
organic material, making prehistoric sites appear to be
much younger than they really are.

Higham and his Oxford colleagues have developed several
techniques, including "ultra-filtration" of dating
samples, to remove more recent carbon. The results are
leading to a reevaluation of radiocarbon dates all over
prehistoric Europe. The most recent installment in this
redating program, reported online today in the
Proceedings of the National Academy of Sciences,
involves the site of Mezmaiskaya Cave in Russia's
northern Caucasus region.

A team led by Higham and Ron Pinhasi, an archaeologist
at University College Cork in Ireland, used the latest
techniques to radiocarbon date the skull bones of a 1-
or 2-year-old Neandertal infant found at the site, which
has been under excavation by a Russian team since 1987.
The team found that the infant most likely died between
42,300 and 45,600 years ago, and an evaluation of the
site's archaeological levels suggested that it was very
unlikely that any Neandertals survived at the cave later
than 39,000 years ago. These new dates are much older
than previous radiocarbon results, which suggested that
Neandertals had hung on at the site until as recently as
30,000 years ago.

Higham and his colleagues went on to conduct a
statistical analysis of previous radiocarbon dating
results from Mezmaiskaya Cave and the six other sites in
Europe and Asia-ranging from Russia in the northeast to
Spain in the southwest-that have provided direct dates
from Neandertal fossils, as opposed to indirect dates
from charcoal and other artifacts. Using a statistical
technique called Bayesian modeling, which calculates the
likelihood that a particular result is valid, the team
concluded that none of these directly dated Neandertal
bones clock in much later than 40,000 years ago.

Neandertals and modern humans were probably like passing
strangers, Pinhasi says. "At this stage" of this ongoing
research, he says, the results "do not support any major
overlap between Neandertals and modern humans" much
after 40,000 years ago, at which time Neandertals were
probably going extinct. Pinhasi adds that "many of the
very young dates, for example, from Gibraltar, are
probably just wrong" due to contamination, mixing of
archaeological layers, and other factors.

Wil Roebroeks, an archaeologist at Leiden University in
the Netherlands, applauds the results: "These dates ...
strongly suggest that the hypothesis of a suggested
overlap of 10,000 years between Neandertals and modern
humans is falsified."

But biologist Clive Finlayson, director of the Gibraltar
Museum and leader of Neandertal excavations at this
British territory at the southern tip of Spain, says
that the late dates of 32,000 years that he and his team
have found for Neandertal occupations in Gibraltar's
caves-which are not based on direct dating of fossils-
are not challenged by the new findings. "This paper is a
typical example of the speculative extrapolation that
... archaeologists and anthropologists often do,"
Finlayson says. "It does not mean that Neandertals did
not survive elsewhere, especially in southern refugia."

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