Extreme cold drove early humans out of Europe

New research is changing our understanding of the climate of Early Pleistocene Europe and what it meant for our early relatives.

Hominin fossils and stone tools indicate that archaic humans had reached Europe by around 1.4 million years ago. Surviving archaeological material related to these initial arrivals is fairly sparse but, until now, it was generally assumed that, once they were present in Europe, they stuck around – in some number – more or less continuously. The information available about the climate of southern Europe at the time supported this conclusion: mostly balmy and warm, with short periods of mild cold weather, the region was also wetter than the Mediterranean today, with plenty of resources on offer. Conditions were thought to have stayed like this until the cold periods became more marked c.900,000 years ago.

However, a new study recently published in Science (https://doi.org/10.1126/science.adf4445) reveals a different story. Previous environmental data had been taken largely from terrestrial sites, and were therefore limited by preservation bias, gaps in the stratigraphic record, and uncertain chronologies. To remedy this, the team focused their research on a deep-sea sediment core taken off the coast of Lisbon, Portugal. They analysed marine micro-organisms and the pollen content of the core to determine how sea temperatures and ecosystems on land changed over time. Researchers also created a simulation model to calculate how these changes in the climate would have affected the environment’s suitability for human occupation.

Marine core sediments reveal that 1.1 million years ago there was a significant drop in temperatures across Europe, which turned the previously comfortable Mediterranean into an environment resembling the semi-arid steppes of Asia today. Early hominin sites in Europe and south-west Asia and their palaeoclimate context support conclusions that these environmental changes drove humans out of the region (above). They are next found in Europe c.200,000 years later, at sites like Happisburgh (below). 

The results suggest that from the time of the first arrival of hominins up until just over a million years ago, the environment was as expected: a series of long stable interglacials and short glacials, perfectly habitable for early humans in the milder climates of western and southern Europe. However, around 1.1 million years ago, it appears there was a dramatic – and previously unrecognised – drop in temperature. This event may have been caused by a longer glaciation, followed by increased melting of polar ice, which disrupted warm ocean currents in the Atlantic. This prompted a decrease in sea temperatures of more than 5°C and affected the climate of the whole continent. The resulting environment was much less well-suited for early humans, who probably did not have the necessary evolutionary adaptations, such as sufficient fat insulation or body hair, or behavioural developments, including effective clothing and shelter or the ability to make fire. In this extreme cold, most of Europe’s small hominin groups would have struggled to survive, and ultimately been driven to extinction. The changing climate also had an impact on the availability of resources: across the continent, the habitability of coastal areas decreased significantly, particularly in the previously favoured regions of western and southern Europe. Plant growth was affected: the Mediterranean would have looked more like the semi-arid steppes of Asia today, dominated by grasses, shrubs, and other plants with less nutritional value. Any groups who survived the initial cold would have been forced to leave the region in search of better resources. Ultimately, the researchers concluded, the environment was just too hostile for Europe’s early human occupants to survive.

What is not certain is the geographic extent of this hominin depopulation, nor how long it took them to come back. If the climatic changes caused humans to leave behind not just Europe but south-west Asia as well, it may have taken quite a while for them to return. It is possible that Europe was empty of hominins for up to 200,000 years – a suggestion supported by the apparent lack of fossils and stone tools in this time period. However, we know that they had re-entered Europe by c.900,000 years ago, thanks to discoveries at several sites, including the famous footprints at Happisburgh, Norfolk, UK (CWA 64). An absence of fossils at Happisburgh makes it impossible to know for certain which ancient hominins created the footprints, but Homo antecessor is the widely accepted choice, as fossils of this species were found at the contemporary site of Atapuerca in northern Spain. Whoever these ancient humans were, we can assume that they were quite different to their earlier relatives – clearly, they were better equipped to deal with the cold.

Further archaeological research will doubtless shed more light on the story of early human occupation in Europe, but the results of this research have revolutionised what we thought we knew about these events, and demonstrate just how important studies of past climates can be.

Text: Amy Brunskill  / Images: Polychronis Tzedakis;  Martin Bates