Neanderthals and Homo Sapiens Tried to Mate for Thousands of Years. Genetics Had Other Ideas

In 1856, two Italian workers at a limestone quarry near Düsseldorf in Germany discovered a basin filled with bones. Initially believing the bones were bear remains, they took them to a local professor who collected specimens. They had no idea that this discovery would lead to significant scientific revelations.

Neanderthal bones. When professor Johann Fuhlrott examined the bones, he realized they didn’t belong to a bear. He identified them as human but recognized they were different from the usual human bones. He then took the find to the University of Bonn and, together with Hermann Schaaffhausen, reported the discovery to the scientific community.

At first, their claims weren’t taken seriously. Some even suggested that the bones belonged to a Russian Cossack suffering from rickets who had been fleeing from Napoleon across Europe.

Almost a decade later, Irish geologist William King proposed a groundbreaking conclusion: Humans hadn’t always been alone on Earth.

But why are we alone now? With the discovery of Homo neanderthalensis, many mysteries emerged. However, one question has haunted scientists for nearly 200 years: Why did Neanderthals disappear? How is it possible for such an ancient and robust species, one that survived numerous challenges, to simply vanish? Why were we left alone?

Over the years, experts have formulated several hypotheses about the disappearance of Neanderthals, ranging from prehistoric genocides to a gradual decline. However, Ludovic Slimak, a researcher at the Center for Anthropobiology and Genomics in Toulouse in France and a leading expert on Neanderthals, has proposed a different perspective.

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The types of love (and what love is not). According to Slimak, a different picture emerges when cultural anthropology insights are applied to paleogenetics findings. In traditional societies where strong identities coexisted, different human communities have exchanged women.

From our contemporary perspective, this practice may seem barbaric. However, anthropology suggests that these crossover processes were essential for establishing stable alliances between different communities. Given that humans possess Neanderthal DNA, this exchange seems to have occurred. Interestingly, Slimak points out that this “fusion” of lineages never fully materialized. The question remains: Why?

A (genetically) impossible love story. According to scientists, Neanderthals and Sapiens interbred and produced offspring. However, a significant portion of these offspring were sterile and unable to reproduce. In other words, although the communities sought to forge relationships and alliances through interbreeding, those attempts often failed.

Searching for answers. “When you are searching for ancient DNA [from 40,000 to 45,000 years ago]… all these early Sapiens have recent Neanderthal DNA, and that's why we have [Neanderthal DNA] today. But when you reach and you try to extract DNA from the last Neanderthals, contemporaries of these early Sapiens–let’s say between 40,000 and 50,000 years ago–there’s not a single Neanderthal with Sapiens DNA,” Slimak told LiveScience.

This observation is intriguing and may provide insight into why the larger and genetically more diverse population of Sapiens ultimately prevailed over the Neanderthals, leaving us as the only surviving species.

Image | Crawford Jolly

Related | We've Long Known That Humans Carry Neanderthal DNA. Now, We’re Starting to Understand Its Implications