Researchers have created a detailed model that tracks how humans spread across Europe during the last Ice Age.
A diverse team from the University of Cologne, which includes experts in geophysics, meteorology, and prehistoric archaeology, has introduced the “Our Way Model.” This model focuses on human movement and population changes from approximately 43,000 to 32,000 years ago during the Aurignacian period. The goal was to gain insights into how the first modern humans populated Europe. This model outlines four distinct phases of human expansion. Initially, there was a gradual settlement from the Levant into the Balkans, followed by a rapid move into western Europe. The third phase experienced a population decline, while the final phase saw increased population density and the exploration of previously uninhabited areas like Great Britain and the Iberian Peninsula. The findings are published in Nature Communications under the title ‘Reconstruction of human dispersal during Aurignacian on pan-European scale.’
The collaboration of climate scientists and archaeologists allowed the team to quantitatively analyze the effect of climate change on human dispersal. Early humans existed as hunter-gatherers for extended periods. As they began migrating across Europe, the climate was markedly different from today. The cooler and drier conditions of the late Last Glacial Period were often alternated with warmer interglacial phases, some of which changed very suddenly while others shifted gradually.
There may have been various factors contributing to human settlement in Europe, including a desire to explore, changes in social structures, and technological advancements. However, the new model has enabled researchers to illustrate how climate change specifically influenced human migration patterns. Earlier models that examined long-term human population movements typically used diffusion-reaction equations, which depict a slow and steady dispersion in all directions while accounting for population growth. Conversely, agent-based models that analyze individual or group motivations to migrate tend to focus on smaller areas. Recent models integrate paleoclimate data, yet they center their calculations on Net Primary Production, which measures carbon storage in ecosystems and is used as an indicator of food availability. The limitation of this method is that it does not account for how accessible or usable these food sources were to humans.
The research team posits that early habitation in Europe involved complex patterns of movement, withdrawal, abandonment, and re-establishment influenced by climatic shifts and human adaptability. The “Our Way Model” simulates human dispersal through two main steps: first, it merges climate and archaeological data to estimate the Human Existence Potential (HEP), and second, it models population dynamics based on the HEP. The HEP assesses the likelihood of human settlement under specific climate and environmental conditions for a certain culture. This metric is generated using a model that incorporates paleoclimatic data from archaeological sites. Employing machine learning, the model delineates climatic factors suitable for Aurignacian peoples, predicting the conditions they preferred. This trained model is then utilized to forecast the spatial and temporal HEP trends using data from the Global Climate Model and oxygen isotope records from Greenland ice cores.
The findings indicate that the first phase involved a slow westward migration from the Levant to the Balkans (around 45,000 to 43,000 years ago), followed by swift expansion into western Europe (approximately 43,250 to 41,000 years ago). Despite facing brief interruptions, the population of Homo sapiens rapidly grew to an estimated 60,000 individuals across Europe during this time. In the subsequent third phase (41,000 to 39,000 years ago), there was a noticeable decrease in both the population size and density, linked to a prolonged cold spell called the GS9/HE4 event that lasted nearly 3,000 years. Nevertheless, the model suggests that humans managed to endure in sheltered areas of significant topography, such as the Alps, which they had occupied in the earlier phase. In the fourth phase, as climatic conditions improved around 38,000 years ago, the population rebounded and expanded into Great Britain and the Iberian Peninsula, consistent with archaeological data.
The HEP maps indicate that, by the end of this process, certain segments of the human populace were more adept at surviving in colder climates, enabling them to expand beyond previously settled territories. “Regional studies often struggle to encapsulate all the contributing factors when trying to reconstruct human migration, especially how these factors interact on different scales and shape long-term trends. This new modeling approach is a significant enhancement,” remarked Dr. Isabell Schmidt from the Department of Prehistoric Archaeology.
For future investigations, the team aims to validate the foundational assumptions of the model by exploring the influence of cultural evolution on the dispersion of humans. The Human and Earth System Coupled Research (HESCOR) project at the University of Cologne will further incorporate aspects of Human-Earth system interactions into the model.
