The reasons why the Neanderthals died off remain a mystery. One of the major theories says that they were the victims of major climate changes, but new evidence suggests that this is an unlikely scenario.
In an age where climate change driven by our own hand is poised to cause catastrophic changes to human life, it seems fitting to work out if shifting climates also doomed our evolutionary cousins, the Neanderthals.
The question of why the Neanderthals died out has been the source of fierce debate since the first bones were discovered in the early 19th century. Some scientists turned the finger of blame inwards, suggesting that early humans killed them off, either directly, through violence and the spread of new diseases, or indirectly by gradually out-competing them.
Others have accused changing climates. According to them, Neanderthals were adapted to cold environments and, being less flexible than humans, they were unable to cope with a warming post-Ice Age world.
Now, Chronis Tzedakis from the University of Leeds has found compelling evidence that the Neanderthals extinction was unlikely to have coincided with the extreme shifts in climate at the end of the last Ice Age.
While their findings don’t rule out the climate change model completely, they strongly suggest that it wasn’t a major factor in the Neanderthals’ downfall.
Looking into the past
This climate theory has been difficult to test until now. It has proven difficult to pin down exactly when the Neanderthals disappeared or what the most likely climate was then.
Archaeologists have attempted to put a date on their extinction with carbon-dating. This technique measures levels of a radioactive form of carbon that is found in all living things and starts to decay when they die.
Carbon-dating is invaluable but it has its problems. It gives figures in ‘radiocarbon years’ that need to be converted into actual calendar years. This calibration becomes less accurate beyond 21,000 years into the past and the Neanderthals died out well before that.
And even if the conversion was done perfectly, it would be very difficult to align these dates with specific prehistoric climates – back that far, the climate record is sketchy and imprecise.
To solve this problem, Tzedakis looked to Cariaco Basin, a remarkable site off the north coast of Venezuela. Cariaco acts as a window into changes in the Earth’s climate over the last half a million years.
It lies in a part of the ocean very sensitive to climate changes, and the large amounts of sediment deposited there tell a detailed story of climatic shifts over time. Among the sediment are the remains of plankton, and by carbon-dating these, scientists can match measurements of radioactive carbon to patterns of climate at the time.
To Tzedakis, Cariaco was a Rosetta Stone, allowing him to compare the carbon-dating estimates of the Neanderthals’ demise to the likely climate at the time.
A tale of three dates
He applied this method to data from Gorham’s cave, a site in Gibraltar that may have been one of the Neanderthals’ last strongholds. It’s a rich source of arrows, spear-heads and other tools and surrounding these are the charcoal remnants of long-extinguished Neanderthal fires.
By carbon-dating the charcoal, scientists originally estimated that Neanderthals lived in the cave till about 30,000-32,000 radiocarbon years ago. Those dates are generally accepted by the scientific community, but newer finds deep within the cave have thrown up more recent and more contentious estimates. These new figures claim that Neanderthals still lived in Gorham’s until about 28,000 radiocarbon years ago, and possibly even as late as 24,000 radiocarbon years ago.
Tzedakis took these three sets of dates, and used the Cariaco data to work out what the world was like at the time. During the time covered by the more conventional estimates (28,000-32,000 radiocarbon years back), the world was going through some mild climatic turbulence, but nothing more than the Neanderthals were used to.
Certainly, Tzedakis found no evidence of the extreme climate shifts that should have preceded the Neanderthals’ extinction, if the climate change model is to be believed. It’s only the youngest of the three dates – 24,000 radiocarbon years ago – that provides a respite for this theory, for that did coincide with a major climate change.
At this time, the ice sheets of the Arctic were expanding and northern Europe was getting colder. But according to Tzedakis’s team, the weather In Gibraltar was fairly stable, with warm water from the tropics counteracting the cooling of the northern continent – the Neanderthals were unlikely to have been affected.
However, the colder northern temperatures may have driven humans into southern Europe, putting them at direct odds with the Neanderthals. In this way, changing climates could have driven them to extinction indirectly, more of a manipulative nudge than a killing blow.
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Reference: Tzedakis, Hughen, Cacho & Harvati. 2007. Placing late Neanderthals in a climatic context. Nature doi.10.1038/nature06117