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Sci Tech
Neanderthals and climate change
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Most extinction dates not near major cold events Competition with modern humans a likely cause
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Whatever it was that sealed the fate of the Neanderthals, it looks unlikely to have been climate change. That is the verdict of a new study that used climate records from Venezuela to deduce what happened at the Neanderthals’ last stand at the southern tip of Europe.
Probable dates
The research suggests that a switch to a cold, dry climate was probably not the telling factor in the demise of the Neanderthals, because of all the probable dates for their extinction, most do not lie near major cold events in the climate record.
Neanderthals (Homo neanderthalensis) lived in Europe until around 30,000 years ago — not long after Homo sapiens arrived on the scene 40,000 years ago.
Different factors
“There are different factors that have been invoked to explain the Neanderthal extinction,” says Chronis Tzedakis of the University of Leeds, U.K., who led the new research. “Clearly the appearance of anatomically modern humans is the prime suspect, but given that the extinction happened during the last glacial period, when climate was changing, what we know is that the climate was extremely unstable at that time.”
The main problem with testing the different theories comes from the difficulty in dating accurately the age of Neanderthal fossils and tools to compare their ages with records of past climate.
This is because ‘radiocarbon dating’ used on Neanderthal remains — in which researchers measure the amount of the radioactively decaying isotope carbon-14 in a sample to determine its age — is not directly related to calendar years.
For very old samples, it can be used to tell whether one object is older than another, but not to determine their exact ages.
Ocean sediments,
Tzedakis and his colleagues got around this problem by comparing the radiocarbon dates of Neanderthal tools from Gorham’s Cave in Gibraltar, with a very accurate set of radiocarbon dates of ocean sediments, in which the lives of tiny sea-creatures record the climate of the time.
These well-dated sediments happen to come from Cariaco Basin, Venezuela. The researchers report in Nature, that of the three main radiocarbon dates given as possible extinction times for the Neanderthals — 32,000 years, 28,000 years and 24,000 years — only the most recent seems to have occurred at the same time as a climate shift.
This most recent date is also the most controversial, meaning that it is generally more likely that it was competition with modern humans, rather than the bitter cold, that did for the Neanderthals.
Influencing climate
The climate in Venezuela is reflective of the climate in Europe, he adds, because many of Europe’s climate shifts involved changes in the Gulf Stream, which influences climate from tropical America to the northern reaches of the Atlantic Ocean.
And large climate swings, from warm and wet to cold and dry, tended to occur more or less all at once globally.
MICHAEL HOPKIN
Nature News Service
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