The study "Pathways at the Iberian crossroads: Dynamic modelling of the Middle-Upper Paleolithic Transition," led by Professor Yaping Shao from the Institute of Geophysics and Meteorology, appears in the journal PLOS One and is part of the HESCOR research project at the University of Cologne, carried out with prehistoric archaeologist Professor Gerd-Christian Weniger. The researchers applied a numerical model to explore possible meetings between Neanderthals and modern humans in Iberia, explicitly incorporating climate fluctuations while simulating population sizes, connectivity, and interactions. Unlike traditional archaeological or genetic approaches that rely on sparse physical evidence, the model can generate and test a wide range of scenarios and thereby provide an additional interpretive framework.
"By linking climate, demography, and culture, our dynamic model offers a broader explanatory framework that can be used to better interpret archaeological and genomic data," says Professor Weniger from the Department of Prehistoric Archaeology. During the transition from the Middle to the Upper Palaeolithic, Neanderthal populations across Europe, particularly in Iberia, declined toward extinction as modern humans expanded across the continent. This interval coincided with pronounced climatic swings featuring alternating cold and warm phases, including rapid warming episodes over a few centuries and slower cooling trends known as Dansgaard-Oeschger events, punctuated by severe cold spells linked to Heinrich events driven by large iceberg discharges into the North Atlantic.
The exact chronology of Neanderthal disappearance and the arrival of modern humans remains unresolved, leaving open the possibility that the two groups overlapped. Genetic comparisons between ancient bones and present-day humans indicate early interbreeding in eastern Europe during initial modern human migrations. Later admixture on the Iberian Peninsula cannot be ruled out due to dating uncertainties, although direct evidence has not been confirmed so far.
"Repeated runs of the model with different parameters allow for an assessment of the plausibility of different scenarios: an early extinction of the Neanderthals, a small population size with a high risk of extinction, or a prolonged survival that would allow mixing," says Professor Shao, principal investigator of the study. Across most simulations, however, Neanderthal and modern human populations did not overlap in space and time enough to interact. In all three main scenarios, population trajectories proved highly sensitive to climate fluctuations, which could either push groups toward extinction or allow them to persist long enough for contact.
In simulations where populations remained stable for longer, the model allowed genetic mixing between Neanderthals and modern humans. In a small fraction of runs, about 1 percent, the final simulated population contained between 2 and 6 percent individuals with ancestry from both groups. According to the model, this admixture would have been most probable in the northwestern Iberian Peninsula, where modern humans could have entered early enough before Neanderthals disappeared entirely.
The team plans to refine both the numerical model and the potential field that underpins it in future work. They intend to add animal populations as potential prey, using vegetation data to construct separate potential fields for humans and animals from combined climatic and geographical inputs. The researchers are also testing whether a specialized machine learning algorithm can help improve these reconstructions and the overall performance of the model.
Research Report:Pathways at the Iberian crossroads: Dynamic modelling of the Middle-Upper Paleolithic Transition
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