Early hunter-gatherers were nearly wiped out by climate change

For centuries, climate change has been a hotly debated topic with far-reaching consequences. But did you ever consider the drastic impact it could have had on prehistoric humans, particularly during the Ice Age in Europe?

A significant new study published in the journal Science Advances has brought to light some chilling facts, revealing how climate change directly influenced the demographics of early European hunter-gatherers. Extreme cold periods caused sharp population declines, even to the extent of near-extinction in the West.

Dental data from prehistoric humans

The research was led by Dr. Hannes Rathmann from the Senckenberg Center for Human Evolution and Palaeoenvironment at the University of Tübingen in Germany. His team adopted a novel approach, focusing on the hardest part of human remains – the teeth.

“Teeth are the hardest tissue in the human body and are therefore the most common fossil skeletal elements found by archaeologists,” noted Dr. Rathmann.

This strategy allowed the researchers to amass an unparalleled dataset, including dental data from 450 prehistoric humans across Europe, covering a time span from 47,000 to 7,000 years ago.

Tracing genetic relationships through teeth

The research team, comprising experts from Germany, Italy, and the United States, analyzed “morphological” tooth traits – small variations such as the number and shape of crown cusps, ridge and groove patterns on the chewing surface, and the presence or absence of wisdom teeth.

“These traits are heritable, which means we can use them to trace genetic relationships among Ice Age humans without requiring well-preserved ancient DNA,” explained Dr. Rathmann.

By also examining hundreds of published photographs of fossils, the team included valuable specimens lost or destroyed during events like World War II.

Climate change and Ice Age connectivity

The researchers found that between 47,000 and 28,000 years ago – during the Middle Pleniglacial – populations in Western and Eastern Europe were genetically well connected.

“This finding is consistent with our previous knowledge from archaeological studies, which identified widespread similarities in stone tools, hunting weapons, and portable art from different regions,” said Dr. Judith Beier from the DFG Center for Advanced Studies Words, Bones, Genes, Tools at the University of Tübingen.

However, during the Late Pleniglacial period (28,000 to 14,700 years ago), the team found no genetic connections between Western and Eastern Europe. Both regions experienced significant reductions in population size and a consequent loss of genetic diversity.

“This drastic demographic change was probably caused by massive climate changes: Temperatures during this period dropped to the lowest values of the entire Upper Paleolithic and culminated in the Last Glacial Maximum,” said Dr. Rathmann.

Shift in Ice Age populations

The harsh climate caused a shift from steppe to tundra landscapes, severely affecting the habitats of prey animals and, consequently, the hunter-gatherers.

“Our results support the long-held theory that populations were not only driven southward by advancing ice sheets but also separated into largely isolated refugia with more favorable environmental conditions,” said Dr. Beier.

Notably, the experts discovered that populations in Western Europe went extinct at the transition from the Middle to the Late Pleniglacial, only to be replaced by new groups migrating from Eastern Europe.

Re-emergence and reconnection

As the Late Pleniglacial concluded, temperatures began to rise, glaciers retreated, and steppe and forest vegetation returned. This allowed the previously isolated and greatly reduced populations in Western and Eastern Europe to grow again, with inter-region migration resuming.

Dr. Maria Teresa Vizzari from the University of Ferrara, a key developer of the study’s machine learning algorithm called Pheno-ABC, emphasized the significance of this approach.

“Our new method has enabled us to reconstruct complex prehistoric demographic events using morphological data. As far as we know, this has never been achieved before,” said Dr. Vizzari.

The Pheno-ABC algorithm identified the most likely demographic scenarios among the many tested, revolutionizing the future analysis of fossil skeletal morphology.

Insights from the Ice Age climate

According to Dr. Rathmann, the study provides important insights into the demographic history of Ice Age Europeans and highlights the profound impact of climate and environmental changes on the lives of prehistoric humans.

“We should urgently learn from our past if we want to address the complex environmental problems of the future,” concluded Dr. Rathmann.

The full study was published in the journal Science Advances.

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