The immediate take home
is that our carbon 14 data is vulnerable to natural contamination
able to make the samples far younger than they are. Again this type
of dating is excellent yet vulnerable to unpleasant surprises.
Unfortunately we draw conclusions that then inform further research
and get really bitten when it comes to archeology. The first trip
around that block was the idea that civilization arose in the middle
east and slowly migrated outward. Correcting ages using 6000 years
of tree rings turned decades of scholarship on its head. Now we have
nicely bumped the Neanderthal to 40,000 years BP or more. I was not
brave enough to say as much on the basis of the time lines that I am
presently working with, but this new dating conforms nicely to my
principal conjecture.
Effectively the first
conjectured modern human expansion around 45,000 to 40,000 years ago
coincides with the plausible subsumation of the Neanderthal linage.
It is also reasonable that a number of other human lineages were also
subsumed. It made little sense that a remnant population would
remain aloof over thousands of years of interaction with a dominant
population.
In the present era, the
native populations of the Americas are been progressively subsumed
into the greater population. It is a slow process that lasts
centuries but the results are still the same that takes advantage of
the reality that people are inclined and generally encouraged to
marry outside their immediate community.
Humanity is wired to
continuously mix their gene pool and the present elimination of
geographic isolation has obviously sped that up. The same happened
40,000 years ago with populations arising on the continental shelf
world wide.
Neanderthals Died
Out Earlier Than Thought
By Charles Cho
These findings hint
that Neanderthals did not coexist with modern humans as long as
previously suggested, investigators added.
Modern humans once
shared the planet with now-departed human lineages, including the
Neanderthals, our closest known extinct relatives. However, there has
been heated debate over just how much time and interaction, or
interbreeding, Neanderthals had with modern humans.
To help solve the
mystery, an international team of researchers investigated 215 bones
previously excavated from 11 sites in southern Iberia, in an area
known as Spain today. Neanderthals entered Europe before modern
humans did, and prior research had suggested the last of
the Neanderthals held out in southern Iberia until about
35,000 years ago, potentially sharing the region with modern humans
for thousands of years.
Their data suggest
that modern humans and Neanderthals may have actually lived in the
area at completely different times, never crossing paths there at
all. Even so, these findings do not call into question whether modern
humans and Neanderthals once had sex— the findings simply indicate
this interbreeding must have occurred earlier, before modern humans
entered Europe.
"The genetic
evidence for interbreeding — 1 to 4 percentNeanderthal DNA in
present-day modern humans — suggests that interbreeding probably
occurred before the period we are looking at in the Levant, the
region around Israel and Syria, when modern humans first migrated out
of Africa," researcher Rachel Wood, an archaeologist and
radiocarbon specialist at Australian National University in Canberra,
told LiveScience.
Dating bones
Scientists discover
the ages of artifacts and fossils using a variety of techniques. For
instance, radiocarbon dating determines the age of biological remains
based on the ratio between the carbon isotopes (atoms of the same
element with different numbers of neutrons) carbon-12 and carbon-14
it holds — this proportion changes as radioactive carbon-14 breaks
down while stable carbon-12 does not. Researchers can also look at
the layers of soil and rock in which objects are found — if these
layers were not disturbed over the years, then objects in the same
layer should be the same age.
The investigators
concentrated on collagen, the part of bone most suited for
radiocarbon dating. Only eight of these bones from two sites in Spain
— Zafarraya Cave and Jarama VI — had enough collagen for
analysis.
One bone, which came
from a wild goat, was found in Zafarraya Cave in a similar layer as
Neanderthal fossils. The bone was previously estimated as 33,300
years in age. However, using an ultrafiltration technique that
cleansed the bone of modern carbon impurities that can give
inaccurate younger dates, they found the bone was more than 46,700
years old.
"Our work
suggests that at present, it is unlikely that Neanderthals
survived any later in this area than they did elsewhere in mainland
Europe," said researcher Thomas Higham at the University of
Oxford in England.
The most surprising
thing "was the enormous difference that the ultrafiltration
dating made to the chronologies of the sites we looked at," Wood
said. "At other sites in Europe, we have seen that this improved
method of dating bone makes a difference, making old bones older.
However, we do not normally see such consistently large differences.
This is probably because the preservation of the organic materials —
bone and charcoal — that are normally radiocarbon dated is really
poor in warm climates like southern Spain."
Analysis of the
remaining samples revealed they were at least 10,000 years older than
previously estimated. Instead, they were close to or more than 50,000
years old, the upper limit for radiocarbon dating.
When Neanderthals died
out
"Our results cast
doubt on a hypothesis that has been broadly accepted since the early
1990s — that the last place for surviving Neanderthals was in the
southern Iberian Peninsula," Wood said. "Much of the
evidence that has supported this idea is based on a series of
radiocarbon dates, which cluster at around 35,000 years ago. Our
results call all of these results into question."
These findings suggest
modern humans and Neanderthals might not have interacted in this
area. In northern Iberia, about 150 miles (250 kilometers) north of
Jarama VI, past research suggested modern humans were only present
starting about 42,000 years ago. These new findings hint that modern
humans and Neanderthals did not coexist for millennia as before
thought, and did not live side-by-side.
"The results of
our study suggest that there are major problems with the dating of
the last Neanderthals in modern-day Spain," Higham said. "We
now have to look very cautiously at the model of late Neanderthal
survival in southern Iberia and focus our efforts on more rigorous
dating programs."
One site, Cueva Antón
in Spain, did seem as young as previously thought. However, it
remains uncertain whether the artifacts there are linked with
Neanderthals — they may belong to modern humans.
The researchers
caution they are not definitely saying that there were no
Neanderthals in southern Iberia after 42,000 years ago. "What we
have is a gap where we have no reliable radiocarbon dates. There
might have been Neanderthals or modern humans or both or neither,"
Wood said. Also, "there are several circumstances which could
have obscured later interbreeding events in Europe, so it is not
possible to say, for example, that at one time there was not more
Neanderthal DNA in Europeans."
The scientists
detailed their findings online Feb. 4 in the journal Proceedings of
the National Academy of Sciences.
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