In most runs, the two groups did not meet.
Fifty thousand years ago, two branches of humanity briefly shared the same peninsula at the edge of the known world — one ancient and fading, one newly arrived and spreading. Researchers at the University of Cologne have now built a computational model to ask whether they ever truly met, finding that such an encounter, while not impossible, was constrained by climate, geography, and the cruel arithmetic of small populations. The question of what passed between Neanderthals and modern humans on the Iberian Peninsula remains open, but science is learning to ask it with greater precision.
- One of prehistory's most enduring mysteries — whether two human species met, mingled, or simply missed each other on the Iberian Peninsula — now has a new tool trained on it: a dynamic computational simulation built by University of Cologne researchers.
- The model must contend with radical uncertainty: climate swung violently during this period, Neanderthal populations were fragile and declining, and the timing of modern human arrival remains imprecise enough to make any conclusion provisional.
- Running thousands of scenario variations, the simulation found that in the vast majority of cases the two populations never crossed paths at all — the landscape was too vast, the groups too sparse, the windows of overlap too narrow.
- Only under a specific convergence of conditions — early modern human arrival in the northwest, a stable enough climate, and Neanderthal populations still barely persisting — did interbreeding emerge as plausible, at roughly one percent probability.
- The research lands in productive ambiguity: genetic evidence confirms mixing happened elsewhere in Europe, but the Iberian case remains unproven, with the model offering a mathematically grounded framework for imagining what could have been.
Somewhere between fifty and thirty-eight thousand years ago, two kinds of humans shared the Iberian Peninsula. One had lived there for hundreds of thousands of years. The other had just arrived from Africa. What happened when they encountered each other — whether they interbred, traded, or simply never met — remains one of prehistory's most persistent questions. Researchers at the University of Cologne have now built a computational model to explore that possibility, and their findings resist any simple answer.
Led by Professor Yaping Shao alongside archaeologist Gerd-Christian Weniger, the team constructed a numerical simulation accounting for climate fluctuations, population size, movement patterns, and the probability of contact during this critical transition. Where traditional archaeology depends on scattered bone fragments and stone tools, and genetics can only reveal what happened after the fact, this model allows researchers to test dynamic what-if scenarios — to watch populations respond to shifting conditions in real time.
The Iberian Peninsula was a volatile place during this era. Climate swung between brief warm spells and prolonged cold periods punctuated by catastrophic iceberg discharges into the North Atlantic. Neanderthals, who had thrived in Europe for two hundred thousand years, were declining. Modern humans were spreading across the continent. The timing of these events remains uncertain enough that an encounter between the two species can be neither confirmed nor ruled out.
Running the model repeatedly across different parameters, the researchers tested three main scenarios: early Neanderthal extinction, a small surviving population, or a prolonged persistence that might have allowed interbreeding. In most runs, the two groups never encountered each other — populations too scattered, the landscape too large, the timing too misaligned. But under a narrow set of conditions, when climate remained stable and modern humans arrived early enough in the northwest before Neanderthals vanished, mixing became possible. The model places this probability at roughly one percent, producing populations where two to six percent of individuals carried genetic material from both species.
Genetic evidence from Eastern Europe already confirms that interbreeding occurred during early human migration into Europe — a fact written into the DNA of many people alive today. On the Iberian Peninsula, where Neanderthals persisted longer than almost anywhere else, the evidence remains ambiguous. The model suggests mixing there was possible but unlikely, hemmed in by climate, geography, and the fragility of small populations in a changing world.
The researchers plan to refine their simulation further, incorporating prey animal populations and machine learning algorithms to process the vast climate and geographical datasets involved. Each iteration promises to narrow the gap between what can be proven and what can be plausibly imagined about those final millennia when two human species shared a continent.
Somewhere between fifty and thirty-eight thousand years ago, two kinds of humans shared the Iberian Peninsula. One had lived there for hundreds of thousands of years. The other had just arrived from Africa, moving into a landscape already occupied. What happened when they encountered each other—whether they fought, traded, interbred, or simply avoided one another—remains one of prehistory's most persistent questions. Now, researchers at the University of Cologne have built a computational model to explore that possibility, and their findings suggest the answer is more complicated than a simple yes or no.
The team, led by Professor Yaping Shao and working with archaeologist Gerd-Christian Weniger, constructed a numerical simulation that accounts for climate, population size, movement patterns, and the likelihood of contact between Neanderthals and anatomically modern humans during this critical transition period. Unlike traditional archaeological methods, which rely on scattered bone fragments and stone tools, or genetic analysis, which can only tell us what happened after the fact, this model allows researchers to test different scenarios dynamically—to ask what-if questions and see how populations might have responded to changing conditions.
The Iberian Peninsula was a particularly volatile place during this era. The climate swung wildly between warm spells that lasted only centuries and longer cooling periods punctuated by catastrophic cold snaps triggered by massive iceberg discharges into the North Atlantic. Neanderthals, who had thrived in Europe for two hundred thousand years, began to decline. Modern humans, meanwhile, were spreading across the continent. The precise timing of these events remains uncertain, which is why a meeting between the two species cannot be ruled out—but neither can it be confirmed.
When the researchers ran their model repeatedly with different parameters, they tested three main scenarios: an early extinction of Neanderthals, a small population barely hanging on, or a prolonged survival that might have allowed interbreeding. In most runs, the two groups never encountered each other at all. The populations were simply too scattered, the landscape too large, the timing too misaligned. But in a narrow set of circumstances—when climate remained stable enough for populations to persist, and when modern humans arrived early enough in the northwest of the peninsula before Neanderthals vanished—mixing became possible. The model suggests this would have happened with only about one percent probability, resulting in populations where two to six percent of individuals carried genetic material from both species.
This finding sits in an interesting middle ground. Genetic evidence from Eastern Europe shows that modern humans and Neanderthals definitely interbred during the early phases of human migration into Europe—a fact written into the DNA of many people alive today. But on the Iberian Peninsula, where Neanderthals persisted longer than almost anywhere else, the evidence remains ambiguous. The model suggests that mixing there was possible but unlikely, constrained by climate, geography, and the fragility of small populations in a changing world.
The researchers are not finished. They plan to refine their model by incorporating animal populations—the prey species that both humans and Neanderthals would have hunted—and by testing whether machine learning algorithms can help them process the vast amounts of climate and geographical data required. Each iteration promises to sharpen the picture of what life looked like in those final millennia when two human species shared a continent, and to narrow the gap between what we can prove and what we can plausibly imagine.
Citações Notáveis
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.— Professor Gerd-Christian Weniger, Department of Prehistoric Archaeology
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.— Professor Yaping Shao, principal investigator
A Conversa do Hearth Outra perspectiva sobre a história
Why build a simulation when we have genetic evidence and archaeological remains?
Because the evidence we have is fragmentary and contradictory. Genes tell us mixing happened in Eastern Europe, but the Iberian Peninsula is a puzzle—the timing is uncertain, the remains are scattered. A simulation lets us ask: given what we know about climate, geography, and population dynamics, was contact even likely?
So you're saying they probably didn't meet?
In most scenarios, no. But that's not the same as saying it's impossible. The model shows that under specific conditions—stable climate, early arrival of modern humans in the right place—mixing becomes plausible. It's about understanding the constraints.
What constraints matter most?
Climate and time. Neanderthals were sensitive to environmental swings. If the climate destabilized, their populations crashed. Modern humans had to arrive before that happened, and in the right region. The northwest of the peninsula was the most likely place, but even there, the odds were slim.
Does this change how we think about Neanderthal extinction?
It suggests extinction wasn't inevitable everywhere at the same time. In some places, populations might have persisted long enough to interact with newcomers. In others, they collapsed before contact was possible. It's less a story of replacement and more a story of variable, local outcomes shaped by climate.
What's next for the model?
We're adding prey animals—the herds that both species hunted. And we're exploring whether machine learning can help us process climate data more accurately. The goal is to move from plausible scenarios to predictions grounded in actual environmental conditions.