New Research Explores Paleolithic Transition from Neanderthals to Anatomically Modern Humans

The transition from the Middle to Upper Paleolithic approximately 50,000–38,000 years ago is marked by the decline and extinction of Neanderthals and the emergence and spread of anatomically modern wise man. Paleoanthropologists from the University of Cologne developed a high-resolution model of population dynamics and used it to reconstruct this transition in Iberia. Using ensemble modeling, they studied the persistence of Neanderthals, the emergence of modern humans, and possible interbreeding.

During the Middle to Upper Paleolithic transition, Neanderthal populations throughout Europe, especially in the Iberian Peninsula, experienced a steady decline, leading to their extinction.

At the same time, anatomically modern humans spread throughout Europe.

This period was also characterized by strong climatic fluctuations with alternating cold and warm phases: phases of rapid warming occurring over just a few centuries contrast with more gradual periods of cooling (the so-called Dansgaard-Oeschger events) that are interrupted by severe cold phases caused by massive releases of icebergs into the North Atlantic (Heinrich events).

The exact timing of the extinction of Neanderthals and the emergence of modern humans remains unclear, so a potential encounter between the two species cannot be ruled out.

Genetic analysis of bones from archaeological sites compared with today's populations points to intermixture in Eastern Europe early in the migration of modern humans.

Late admixture of the two populations in the Iberian Peninsula is possible due to significant dating uncertainty, but has not yet been proven.

In their study, University of Cologne professor Yaping Shao and his colleagues used a numerical model to simulate the possibility of both groups meeting on the Iberian Peninsula.

The model takes into account prevailing climate variations and simulates the populations of both groups, as well as their connectivity and interactions.

“Repeated runs of the model with different parameters allow us to assess the plausibility of different scenarios: early Neanderthal extinction, small population size with high risk of extinction, or long survival allowing admixture,” Professor Shao added.

“However, in most races the two groups did not meet.”

In all three scenarios, the population is very sensitive to climate fluctuations.

In cases where the population could remain stable long enough, mixing of the two species was possible.

There is a low probability (1%) that at the end of the simulation there will be a small fraction of 2 to 6% of the total population that has genes from both groups.

This mixing most likely occurred in the northwestern Iberian Peninsula, an area where modern humans may have arrived early enough before the Neanderthal population disappeared completely.

“By linking climate, demography and culture, our dynamic model offers a broader explanatory framework that enhances the interpretative power of archaeological and genomic data,” said University of Cologne professor Gerd-Christian Weniger.

A paper the results appear online in the journal PLOS ONE.

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Yu Shao etc.. 2025. Pathways at an Iberian Crossroads: Dynamic Modeling of the Middle-Upper Paleolithic Transition. PLOS One 20(12):e0339184; doi: 10.1371/journal.pone.0339184