Big chill killed off the Neanderthals

19:00 21 January 04

who, killed humankind's nearest relatives, the Neanderthals who once roamed Europe before dying out almost 30,000 years ago?

Suspects have ranged from the climate to humans themselves, and the mystery has deeply divided experts. Now 30 scientists have come together to publish the most definitive answer yet to this enigma.

They say Neanderthals simply did not have the technological know-how to survive the increasingly harsh winters. And intriguingly, rather than being Neanderthal killers, the original human settlers of Europe almost suffered the same fate.

The last ice age

Led by Tjeerd van Andel of the University of Cambridge, a team of archaeologists, anthropologists, geologists and climate modellers have compiled a vast new set of biological, environmental and social evidence on life between 20,000 and 40,000 years ago.

It includes data from sediment cores and 400 or so archaeological sites, and information gleaned from fossil bones and stone tools. To this they have added the most up-to-date climate models, and radiometric dates of human and Neanderthal sites and artefacts.

Seasonal migration

The result is a definitive series of maps covering climate change over time, the appearance of animal and plant populations, and how human and Neanderthal communities migrated with the seasons. The resolution is so good that, for the first time, researchers can reliably trace the movements of both hominid species.

Ice cores recovered from Greenland in the 1970s show that Europe's climate varied hugely during the last ice age, especially in the period between 70,000 and 20,000 years ago. Cold glacial periods were punctuated by warmer times, and the average temperature could rise and fall several degrees within a decade or so.

Studies of permafrost patterns, the remains of small animals and pollen grains, as well as fossil bones, show that such changes had a dramatic effect on the flora and fauna of the time, including Homo sapiens and Neanderthals.

The maps show that, facing temperatures that plummeted to -10°C in winter (see map), Neanderthals retreated south from northern Europe 30,000 years ago, a migration which coincided exactly with the southern march of the ice sheets (Neanderthal and Modern Humans in the European Landscape of the Last Glaciation: Archaeological Results of the Stage 3 Project).

It is surprising "the extent to which Neanderthals seem to have been deterred by the cold, and retreated as the going got tough," says archaeologist William Davies, a co-editor of the report based at University of Southampton, UK.

Last refuge

The maps also reveal that the earliest modern humans, the Aurignacian people, who appeared around 40,000 years ago, could not cope with the glacial cold either. They retreated south until 25,000 years ago when they were reduced to a few refuges, such as southwest France and the shores of the Black Sea.

The new maps show that even at the height of the last glacial period, 18,000 to around 22,000 years ago, continental Europe supported extensive grasslands which were fodder for huge numbers of migrant animals such as reindeer and bison.

The archaeological evidence strongly suggests that both hominids coexisted in southern Europe for thousands of years, but competed for ever diminishing resources. And that might have been the end for both Homo sapiens and Neanderthals but for the arrival of the technologically advanced Gravettians.

The Gravettians appeared in eastern Europe 29,000 to 30,000 years ago complete with flash new tools, such as javelin-like throwing spears and fishing nets, which allowed them to catch a greater range of prey.

They also had clothing to keep the cold out, such as sewn furs and woven textiles, and possibly more specialised social structures. Their ability to tough out the colder climes dominating Europe 18,000 to 25,000 years ago revitalised the human population.

Adapt to survive

The Neanderthals, however, without either new blood or new technology, found it impossible to survive and died out, probably around 28,000 years ago.

For Neanderthal expert Paul Pettitt of the University of Sheffield, UK, the evidence that climate adversely affected the Aurignacian people as much as the Neanderthals is fascinating. When the going got tough in northern Europe, says Pettitt, both adopted a "get out of the kitchen strategy".

In contrast, Gravettians used their technological prowess "to reorganise the way the kitchen was used". Pettitt says that step was just as revolutionary as becoming modern Homo sapiens in the first place.