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Prehistoric World

Freeze Condemned Neanderthals

Edited from BBC News, 20 February 2007

A sharp freeze could have dealt the killer blow which finished off our evolutionary cousins the Neanderthals, according to a 2006 study.

These ancient humans were generally thought to have died out in most parts of Europe by about 29,000 to 30,000 years ago. And in 2006, new data from their last known refuge in southern Iberia indicated that the final population was probably beaten by a cold spell some 24,000 years ago.

The research was reported by experts from the Gibraltar Museum and from Spain. They said that 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 showed that 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.

Southern refuge

Neanderthals appear in the fossil record about 350,000 years ago and, at their peak, these squat, physically powerful hunters dominated a wide range, spanning Britain and Iberia in the west to Israel in the south and Uzbekistan in the east.

Our own species, Homo sapiens, evolved in Africa. They displaced the Neanderthals in the Near East and then did the same in Europe after beginning to enter it about 40,000 years ago. During the last ice age, the Iberian peninsula was a refuge in which Neanderthals lived on for several thousand years after they had died out elsewhere in Europe.

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 some 30,000 years ago.

Southern Iberia appears to have been sheltered from the worst of these. But about 24,000 years ago, conditions deteriorated there too. This event was the most severe the region had seen for 250,000 years. The research findings were published in the journal, Quaternary Science Reviews.

Rare event

The cold event seems to have been pretty severe and also quite short. Plants such as olive trees and oak trees, 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 chill may have been cyclical changes in the Earth's position relative to the sun - so-called Milankovitch cycles.

But a rare combination of freezing polar air blowing down the Rhone valley and Saharan air blowing north seems to have helped cool this part of the Mediterranean Sea, contributing to the severe conditions. 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.

Neanderthals' last outpost
Neanderthals' last outpost - (top) Gibraltar today with a series of caves at its base. Gorham's is second from the left. (Bottom) a reconstruction of late Neanderthal times. The sea is down by 80-120m. Exposed is a marshland, plains environment, rich in food resources which the Neanderthals exploited

However, in an interesting new development, scientists in 2007 were also now reporting another site, from south-eastern Spain, which had yielded evidence for the late survival of Neanderthals.

In a study which was published in the journal, Geobios, a team from the University of Murcia analysed pollen from soil layers at Carihuela cave to determine how vegetation had changed in the area during the past 15,000 years. They also obtained ages for sediment samples from the cave, using radiocarbon dating and uranium-thorium dating.

Sediment layers containing Neanderthal tools were found to date from 45,000 years ago until 21,000 years ago.

Caution needed

These radiocarbon dates were 'raw', and did not exactly correspond to calendar dates. They could not therefore be compared directly with those from Gibraltar, which had been calibrated.

Spanish archaeologists carried out a detailed excavation of Carihuela between 1979 and 1992. But the cave was closed at the time of this report due to a dispute between national and regional governments over rights to dig there. Neanderthal bones were also excavated from these sediment units, including a male skull fragment which could potentially be very recent. But the team leader, Professor Carrion, was reluctant to draw conclusions.

The bones had been recovered in various excavation campaigns over the course of fifty years. The relationship between them and the dates provided needed to be treated with caution. Professor Carrion pointed out that sediments in parts of the cave could have been churned up, mixing old bones in with younger material.

However, there remained the hope that the late Neanderthal dates from Carihuela may have agreed well with those from Gibraltar once they had been calibrated.

Neanderthal Sites
Principal sites showing the most recent evidence of Neanderthals - notice how the later populations are all congregated in Iberia



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