Sudden cold snap linked to Neanderthals' demise
Thursday, 22 February 2007
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They once inhabited a zone stretching from Asia to western Europe and eked out an existence until some 24,000 years ago. But in the end it was a familiar foe - climate change - that did for our evolutionary cousins the Neanderthals, new research suggests.
The ancient population found their last refuge in the Gibraltar area, where the diverse plant life, animals, sandy plains, woodlands, wetlands and coastline enabled them to maintain their lifestyle. But then came a sharp downturn in temperatures which, scientists say, may have dealt the Neanderthals a killer blow in southern Iberia.
Professor Clive Finlayson from the Gibraltar Museum, who revealed evidence last year of late generations of Homo neanderthalensis, said sediment cores drilled from the seabed near the Balearic Islands showed how they died out.
The cores reveal the average sea-surface temperature there plunged to 8C (46F), compared with modern sea-surface temperatures of between 14C (57F) and 20C (68F). They also showed that higher levels of sand were deposited in the sea and the amount of river water running into the sea also plummeted.
"[The chill] looks pretty severe and also quite short," Professor Finlayson told the BBC. "Things like olive trees and oak trees that are still with us today managed to ride it out. But a very fragmented, stressed population of Neanderthals - and perhaps other elements of the fauna - did not."
The cause of this big freeze is unclear. It may have been cyclical changes in the Earth's position relative to the Sun - so-called Milankovitch cycles. A rare combination of freezing polar air from the Rhône valley and Saharan air blowing north seems to have helped cool this part of the Mediterranean Sea, contributing to the severe conditions.
If the findings, published in Quaternary Science Reviews, are correct, climate change put paid to a extraordinarily durable creature. The Neanderthals survived in the Iberian peninsula long after those living elsewhere in Europe had died out. Squat, powerful hunters, they appear in the fossil record about 350,000 years ago and, at their peak, dominated much of the northern hemisphere, from Britain in the west to Israel in the south and Uzbekistan in the east. Southern Iberia served as a habitat for the last of them because it provided shelter from the worst of the frequent, rapid changes in climate which hit a peak 30,000 years ago.
But eventually, the change in climate appears to have become too pronounced - even for them. It seems to have caused a drought, placing pressure on the last surviving Neanderthals by reducing their supplies of fresh water and killing off the animals they hunted. The event was the most severe the region had seen for 250,000 years.
The revelation comes amid new scientific debate about which areas the last of the Neanderthals actually occupied. In another study published in the Spanish journal Geobios, scientists from the University of Murcia announced the discovery of sediment layers at a cave in Carihuela, in north-east Spain, containing Neanderthal tools that date from 45,000 years ago until 21,000 years ago - suggesting life after those in Gibraltar. But Professor Jose Carrion, who headed the team, is cautious about jumping to conclusions. "The human bones have been recovered in different excavation campaigns over 50 years. The relationship between them and the dates I provide must be treated with caution," he said.
Professor Finlayson suggested the late Neanderthal dates from Carihuela might agree with those from Gibraltar after they have been calibrated. Our own species, Homo sapiens, evolved in Africa, and eventually displaced the Neanderthals after entering Europe about 40,000 years ago.
