Ice Age climate shifts changed early human migration patterns

More than 12,000 years ago, Europe’s prehistoric hunter-gatherers faced extreme shifts in climate. These changes, brought on by the final stages of the Ice Age, had a powerful effect on how the human population lived, where they moved, and how many of them could survive.

A new study traces how these ancient communities responded to both warming and cooling periods, revealing large swings in population size and movement across the continent.

The research was led by a team of 25 archaeologists, including scientists from the University of Cologne, and involved experts from twenty European universities and institutions.

Their findings, recently published in PLOS One, focus on the Final Palaeolithic period, between 14,000 and 11,600 years ago.

This study provides a clearer picture of population growth, decline, and migration in response to two major climate phases: a warm period known as Greenland Interstadial 1d-a (GI-1d-a), and a sharp cold snap called Greenland Stadial 1 (GS-1), also known as the Younger Dryas.

Climate-driven boom and bust

During the warmer GI-1d-a period, early humans began expanding into northern and northeastern central Europe.

This marked a turning point, as these areas became major population centers for the first time in prehistory.

At the same time, parts of southwestern Europe – especially Spain and France – saw a decline in population compared to earlier Upper Palaeolithic periods.

But when the climate took a dramatic turn during GS-1, the population across Europe dropped sharply. Researchers estimate that during this cold phase, the number of people was reduced by half.

Despite this overall collapse, the pattern wasn’t uniform. Some regions bucked the trend. Parts of northern Italy, Poland, and northeastern Germany actually saw stable or slightly rising population numbers.

These pockets of resilience suggest that some groups migrated eastward to seek more livable conditions.

“These observations probably reflect the eastward movement of people in response to the very abrupt and pronounced climatic cooling during the Younger Dryas,” explains Dr. Isabell Schmidt from the University of Cologne’s Department of Prehistoric Archaeology.

“Humans during the Final Palaeolithic apparently responded by migrating to more favourable areas.”

Mapping the past with modern tools

To track these demographic shifts, the researchers compiled a comprehensive database of archaeological sites from the Final Palaeolithic.

They then applied a geostatistical method known as the Cologne Protocol to estimate how many people lived in each area and how densely populated those regions were.

This standardized method helps archaeologists compare population data across time and space more reliably.

The study highlights how early humans didn’t just endure climate change – they responded to it.

By moving into new territories or concentrating in more stable regions, they adapted their way of life to changing temperatures and environmental stress.

This pattern of climate-driven migration adds a new layer of understanding to our species’ long history of survival and adaptation.

Europe has seen climate-linked population drops before

This isn’t the first time Europe saw a large population decline during prehistory.

The researchers point out that a similar drop happened during the late Gravettian period, roughly between 29,000 and 25,000 years ago, when colder temperatures wiped out regional groups and reduced populations in western and central Europe by up to two-thirds.

Still, there’s much left to learn. Early demographic changes remain difficult to trace with precision, but this study adds new evidence to a growing pool of research.

By looking closely at how ancient humans handled the ups and downs of the Ice Age, this research brings us one step closer to understanding the deep history of human resilience – and how that resilience may still guide us in facing today’s environmental changes.

The work was part of the long-running Collaborative Research Centre 806 – Our Way to Europe, based at the University of Cologne and funded by the German Research Foundation between 2009 and 2021.

It is now being continued under the HESCOR project (Human and Earth System Coupling Research), supported by the Ministry of Culture and Science of the State of North Rhine-Westphalia.

The full study was published in the journal PLOS One.

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