Climate Change Killed Neandertals, Study Says

Hillary Mayell
for National Geographic News

February 9, 2004

Both Neandertals and the first humans to reach Europe struggled with the changing conditions brought by increasingly cold temperatures, according to a study by 30 scientists.

The two species coexisted in Europe from roughly 45,000 to 28,000 years ago when the Neandertals died out. Why humans survived and the Neandertals didn't has puzzled archaeologists for over a century.

Theories have ranged from interspecies genocide to interbreeding to humans' superior communication skills, hunting technology, and social organization.

The new study—a seven-year effort that combined the work of 30 scientists from 11 nations—suggests, however, that the inability to adapt to climate change led to the Neandertals' demise.

"It's not that it got too cold for them; both humans and Neandertals had clothing such as fur mantles," said Jerry van Andel, a geologist at the University of Cambridge in the United Kingdom who led the study.

Rather, researchers believe Neandertals failed to adapt their hunting methods when big game species like mammoth (Mammuthus primigenius), bison (Bison bonasus), and red deer (Cervus elaphus) fled south and the once-forested landscape of Europe changed into a sparsely vegetated steppe and half desert during the last Ice Age.

Neandertals, who once relied on forest cover to sneak up and club or stab herd animals, proved far less effective hunters when stalking new, more dispersed game animals, especially without camouflage. Eating less, Neandertals grew weak, succumbing more often to disease and other threats. While early humans also struggled, they ultimately survived their changing environment.

"The big advantage modern humans had was improved hunting technology, a more complex social organization, and expanded use of resources that allowed them to move from a more sedentary lifestyle to adapt to the conditions wrought by colder temperatures," he said.

The study, Neanderthal and Modern Humans in the European Landscape of the Last Glaciation, was published last month by the McDonald Institute for Archaeological Research Monographs.

Myth of Cold-Adapted Species

Scientists combined data on temperature, landscape, and vegetation of the paleoenvironment with maps of archaeological sites and plotted how these variables changed over time. This enabled them to track the movements of both Neanderthals and early humans.

Their findings punctured the long-held idea that Neandertals were a "cold-adapted" species. The theory holds that Neandertals' shorter limbs and massive trunks (traits seen in populations living in Arctic conditions today) made them physiologically well suited to live in colder temperatures.

"Neandertals had about the same resistance to cold and love of warmth as the early humans who came around 45,000 years ago," said van Andel. "There was not really much difference between them."

"People often think of the Ice Age as a monolithic period lasting close to 100,000 years, with frigid temperatures and glacial landscapes," said David Pollard, a paleoclimatologist at Pennsylvania State University who participated in the study. "Across Europe, beginning around 60,000 years ago, temperatures were in the range of 5° Celsius colder than present—significantly warmer than what you would see in a full ice age."

That started changing around 40,000 years ago. As temperatures dropped, ice caps crept farther south, snow cover increased, and both humans and Neandertals moved south.

"When things start to turn nasty, both the Neandertals and the Aurignacians"—the earliest group of humans in Europe—"were forced to retreat," said William Davies, an archaeologist at the Centre of the Archaeology of Human Origins, University of Southampton, England.

Still, it wasn't the cold that did in the Neandertals, the scientists say.

Following the Herds

When humans first arrived in Europe 45,000 years ago, they shared many cultural traits with the Neandertals. Both had mastered fire, flaked stone to make tools, ate nearly all-meat diets, tended their injured, and occasionally buried their dead. Both used fur and animal skins for warmth.

Temperatures in Europe were relatively mild. Forests and grasslands dominated the landscape. Big game was plentiful.

"Both tribes—Neandertals and Aurignacians—were pretty well adapted to this environment, and didn't have to move around a lot to survive," said van Andel.

As temperatures became colder, the vegetation that sustained the large herbivores disappeared. Bison, mammoths, red deer, and other animals moved south, and the Neandertals and early humans followed them.

But more than just temperature had changed.

"Instead of finding animals in groups in open wood and grass land, where hunters could sneak up on large herds, the new landscape was half desert or steppes," said van Andel. "Catching animals in that environment is much more difficult because you can't sneak up on them and they don't form large herds."

Sneaking up on a huge animal, cutting it out of a herd and clubbing or stabbing it to death was always treacherous business. Neandertal skeletons reveal they lived brutal lives, sustaining many broken bones and concussions. They rarely lived beyond their 30s. The new hunting environment proved far more dangerous, with less success.

"This is what made it impossible for the Neandertals to survive," said van Andel. "With less food, they became more susceptible to illness, reproduced more slowly, starvation became more of a factor, and the population died out very, very slowly."

Adaptation is Key

Meanwhile, the Aurignacians didn't fare much better.

"They also found themselves in the steppes and couldn't hang in there," said van Andel. Population numbers dropped drastically.

The Aurignacian retreat began somewhat later than that of the Neandertals, who had abandoned northern sites by around 37,000 years ago, moving south and west toward Iberia (present-day Spain and Portugal).

Evidence suggests the Aurignacians may have been gradually developing the sophisticated tools, trade networks, and expanded use of raw materials that might have ensured their survival.

But by 33,000 years ago, a second group of humans, the Gravettians, had largely supplanted the Aurignacian in many areas of Europe.

Whether the Gravettians moved into Europe from Central Asia, or, more likely, simply evolved separately in the northern plains of Germany, Poland, and farther east, their improved technology and more complex social organization enhanced their ability to survive in colder climes.

Weapons like the throwing spear enabled hunters to kill or wound their prey from a distance. Evidence suggests they used plant fibers to make fishing nets and snares for small mammals. Extended trade networks allowed tribes to become more mobile and follow the caribou, mammoth, and other mammals as they migrated south in the winter and north in the summer.

"The Gravettians were able to make the social adaptations to survive in a more Arctic climate," said Davies, co-editor of the final report. "By about 30,000 years ago, you see quite large occupation sites. In central Europe there is evidence of the use of plant fibers to make nets and clothing. Clay, bone, and ivory were used in tools and weapons, and the diet expanded to include fish and birds."

By 25,000 years ago, the Aurignacian culture had virtually disappeared, confined to a few small pockets scattered across southern Europe.