|27 February 2007
Freeze 'condemned Neanderthals'
A sharp freeze could have dealt the killer blow that finished off our evolutionary cousins the Neanderthals, according to a new study.
The ancient humans are thought to have died out in most parts of Europe by about 35,000 years ago. And now new data from their last known refuge in southern Iberia indicates the final population was probably beaten by a cold spell some 24,000 years ago.
The research is reported by experts from the Gibraltar Museum and Spain. They say a climate downturn may 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.
Sediment cores drilled from the sea bed near the Balearic Islands show the average sea-surface temperature plunged to 8C (46F). Modern-day sea surface temperatures in the same region vary from 14C (57F) to 20C (68F). In addition, increased amounts of sand were deposited in the sea and the amount of river water running into the sea also plummeted.
Our own species, Homo sapiens, evolved in Africa, and displaced the Neanderthals after entering Europe about 40,000 years ago. During the last Ice Age, the Iberian Peninsula was a refuge where Neanderthals lived on for several thousand years after they had died out elsewhere in Europe. These creatures (Homo neanderthalensis) had survived in local pockets during previous Ice Ages, bouncing back when conditions improved. But the last one appears to have been characterised by several rapid and severe changes in climate which hit a peak 30,000 years ago.
Southern Iberia appears to have been sheltered from the worst of these. But about 24,000 years ago, conditions did deteriorate there. This event was the most severe the region had seen for 250,000 years, report Clive Finlayson, from the Gibraltar Museum; Francisco Jimenez-Espejo, from the University of Granada, Spain; and colleagues. The cause of this chill may have been cyclical changes in the Earth's position relative to the Sun - so-called Milankovitch cycles.
Gorham's Cave on Gibraltar shows evidence of occupation by groups of Neanderthals until 24,000 years ago. But thereafter, researchers have found no signs of their presence. However, scientists are also now reporting another site, from south-east Spain, which has yielded evidence for the late survival of Neanderthals. Sediment layers containing Neanderthal tools were found to date from 45,000 years ago until 21,000 years ago. These radiocarbon dates are "raw", and do not exactly correspond to calendar dates. They cannot therefore be compared directly with those from Gibraltar, which have been calibrated with calendar dates.
Source: BBC News (20 February 2007)
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