Did humans or climate push Neanderthals over the edge?

AAbout 40,000 years ago, a group of primitive humans settled in the Iberian Peninsula, a region of Europe considered a refuge for Neanderthals.

Researchers aren’t entirely sure what happened next. Previous genetic studies suggest that Neanderthals and early humans interbred in some areas, including Eastern Europe and Southwest Asia, but it is unclear whether this also happened on the Iberian Peninsula.

To learn more about possible Iberian clashes, as well as migration patterns on the peninsula, a team of scientists from the University of Cologne in Germany carried out a series of simulations integrating ancient climate data, as well as archaeological evidence of human and Neanderthal presence at sites in the region.

Read more: “It turns out the human family tree is complicated”

Scientists applied the model to several different scenarios: an early extinction of Neanderthals, a small Neanderthal population highly vulnerable to extinction, or longer survival of Neanderthals that would allow them to mix with our ancestors. Evidence of past climates, gleaned from sources such as peatlands and marine sediments, has helped determine whether a specific region, over a certain period of time, would be suitable for humans or Neanderthals. This period was characterized by dramatic variations between cold and warm temperatures.

In each of the scenarios simulated by the researchers, Neanderthals were threatened by climate change. But there was still a small chance that the species had maintained stable populations long enough to mate with humans. Overall, the model estimates that there is a 1 percent chance of genetic mixing between the two species and that a total of about 2 to 6 percent of all Neanderthals and humans have genes from both species. The results were reported in PLOS One.

This fraternization was more likely to occur in the northwest of the Iberian Peninsula, the model suggests. Here, modern humans may have settled before the disappearance of the Neanderthals.

In future research, the team hopes to incorporate more information to make the simulations more realistic, including data on which animals may have served as prey, providing a clearer picture of possible interbreeding between our ancestors who survived and those who went extinct.

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Main image: Alicia G. Monedero / Shutterstock

• Molly Glick

  Published on December 22, 2025

  Molly Glick is the newsletter editor of Nautilus.