Genetic clues tell the story of Neanderthal decline

Analysis of Neanderthal DNA has helped piece together the story of the many millennia of hard times that ultimately led to the extinction of our ancient human relatives.

Faced with a cold climate, their population dwindled and they ended up confined to what is now southwestern France. Later, the climate warmed and Neanderthals began to roam more. But most of their genetic diversity was lost, so even widely dispersed groups had very similar DNA.

This situation – small, isolated groups with little genetic diversity – may have contributed to their eventual extinction.

Neanderthals lived in Europe and Asia for hundreds of thousands of years, disappearing from the archaeological record about 40,000 years ago. Previous studies of their DNA have shown a drastic shift in their genetics towards the end. Late Neanderthals, those who lived about 60,000 years ago, were both genetically similar and different from those who came before. “Toward the end of Neanderthal history, there must have been a population turnover,” he says Cosimo Posth at the University of Tübingen, Germany.

To find out how this turned out, Posth and his colleagues obtained DNA from 10 Neanderthals from six sites in Belgium, France, Germany and Serbia. In each case, they sequenced mitochondrial DNA, which is inherited only from the mother. They compared the new mitochondrial genomes with 49 that had already been read.

Neanderthals, who lived between 60,000 and 40,000 years ago, almost all belonged to the same lineage that arose about 65,000 years ago. Other lineages that were present in earlier periods were absent. “This is a very strong indication that this is indeed a population turnover,” says Posth.

The team also looked at a database of Neanderthal archaeological sites. “Between 80,000 and 70,000 years ago, there was a large geographic reduction towards southwestern Europe and especially a very high density of sites in southwestern France,” says Posth.

Climate shifts may explain why. “About 75,000 years ago, the great glaciation begins,” says Posth. “We think this is the event that triggered the Neanderthal rush towards southwestern Europe.”

The new lineage appears to have originated in southwestern France and subsequently spread from there after 60,000 years when the climate warmed again. While the new lineage spread and appeared as far east as the Caucasus, the population does not appear to have increased significantly.

One exception to this trend is the Thorin individual, found at Grotte Mandrin in France. Although Thorin’s DNA dates back only 50,000 years, it suggests that he belonged to one of the older lines – at least one of which seems to have survived the population contraction. Posth says that Thorin is “the only specimen that doesn’t fit the story”.

Being able to reconstruct Neanderthal movements in this way is a significant benefit, he says Tharsika Vimala at the University of California, Berkeley, who participated in Thorin’s studies.

Previous studies have also identified contractions and expansions in the Neanderthal population in which some lineages were lost, Vimala says. For example, a 2021 study found evidence population turnover about 100,000 years ago. “That was also explained by the climate,” he says.

Neanderthals’ habit of living in small, isolated groups may have put them at greater risk of extinction. “They migrated in small groups,” says Vimala of studies estimating Neanderthal group sizes. between three and 60. Posth says this may have allowed harmful genetic variants to accumulate and also made each group more vulnerable to random events.

Discovery Tours: Archaeology, Human Origins and Paleontology

New Scientist regularly reports on the many amazing places around the world that have changed the way we think about the dawn of species and civilizations. Why not visit them yourself?

topics:

• Neanderthals/
• ancient people