FAU prehistorians contribute finds from the University’s own Sesselfelsgrotte cave to an international study

Late Neanderthals are believed to have descended from a small group that survived extreme Ice Age conditions in southwestern France. In collaboration with an international team, researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have confirmed the “bottleneck theory” and dated it more precisely in a new study: Their findings suggest that both the geographic distribution and the genetic diversity of the pan-European Neanderthal population declined dramatically within a short period of time approximately 65,000 years ago. Subsequently, the surviving Neanderthals spread out from a small, isolated refugium to repopulate their former habitats until their extinction approximately 42,000 years ago. The study incorporated new DNA samples – including one from a Neanderthal fetus found in FAU’s own Sesselfelsgrotte cave in the Altmühl Valley. The findings of the study have been published in the renowned journal PNAS.*

The first Neanderthals emerged approximately 300,000 years ago. They settled in large parts of Europe and spread as far as southern Siberia. “We still don’t have a comprehensive understanding of Neanderthal population history, nor of the demographic processes that led to their extinction,” says Prof. Dr. Thorsten Uthmeier, Chair of Prehistoric Archaeology and the Archaeology of Prehistoric Hunter-Gatherers at FAU. “Maps of archaeological sites suggest that an event occurred during the last glacial period that caused a rapid decline in the geographic distribution and genetic diversity of the early population.” It was believed that only a small group survived and that all later Neanderthals descended from this group. In genetics, such processes are referred to as ‘bottlenecks’.”

DNA samples provide new insights

To test and refine the bottleneck theory, an international research team led by the University of Tübingen analyzed ten new mitochondrial DNA sequences (mtDNAs) from Neanderthal remains found at six archaeological sites in Belgium, France, Germany, and Serbia and compared them with 49 previously published mtDNAs. “The mtDNA samples do not come from the cell nucleus, but rather from the mitochondria – single-celled structures that regulate a cell’s energy metabolism and have their own DNA,” explains Uthmeier. Mitochondrial DNA is used in archaeological research because it is more stable, occurs in greater quantities, and is easier to analyze than nuclear DNA. One of the new mtDNA samples included in the study comes from a Neanderthal fetus that was discovered in 1968 by FAU researchers in the Sesselfelsgrotte cave in the Altmühl Valley near Kelheim, Germany. The preparatory work at FAU was conducted as part of the project “SHARP – Testing hypotheses on the transition from Neanderthals to Homo sapiens at the Paleolithic site of Sesselfelsgrotte,” which began in 2023 and is funded by the National Geographic Society.

From the samples, researchers can identify lineages. “mtDNA mutates much less frequently than nuclear DNA, which plays a key role in determining our appearance and physical constitution, among other things,” says Thorsten Uthmeier. “However, the degree of diversification in the mtDNA samples provides an insight into how closely related the Neanderthal groups – from which the bone and tooth fossils originate – were to one another.” Innovative analytical methods, such as decoding genetic information by breaking DNA down into individual gene sequences, made it possible to include samples in the study that had previously proven impossible to analyze. By comparing the newly decoded mtDNA with existing mtDNA, researchers have now been able not only to establish kinship but also to estimate ages based solely on genetic data. The ability to determine the age of samples in this way is an important development, as conventional dating methods have proven unsuitable for dating a great many samples. The combination of these methods has made it possible to reconstruct temporal and spatial patterns in the distribution of late Neanderthals.

A refugium in France 65,000 years ago

The study’s findings suggest that the last bottleneck event – which is believed to have played a major role in the extinction of the Neanderthals – occurred around 65,000 years ago. According to Uthmeier, “as recently as 130,000 years ago, Neanderthals were widespread throughout Western Eurasia, predominantly in what is now northern Germany and Belgium. There were isolated groups in the Caucasus, and even one in the Altai Mountains in southern Siberia.” Over the course of just tens of thousands of years, both genetic diversity and the range of the species declined, and its core population shifted increasingly toward southwestern France. “We suspect that the climatic conditions 65,000−60,000 years ago, a very cold and dry period, triggered the retreat to this refugium and the extinction of the remaining Neanderthal lineages,” explains Uthmeier. Subsequently, the Neanderthals began to populate a much wider area again, with virtually all later Neanderthals descendants of the group originally based in southwestern France.

There is, however, one exception: During excavations in the heart of the refugium, in Mandrin Cave in the Rhône Valley, the skeleton of a Neanderthal was found and named Thorin. There is evidence that he lived past the bottleneck, but his mtDNA differs significantly from that of the other survivors and should actually have become extinct. “Until recently, it was thought that Thorin belonged to an isolated group that had remained in a very small area,” says Uthmeier. “However, the genetic analysis now conducted has shown that the fetus from the Sesselfelsgrotte in the Altmühl Valley, whose remains date from a similar period, was also related to this group. The Thorin line was apparently more widespread than previously thought. This finding really surprised us.”

The researchers were also able to provide data to answer the question of when and why Neanderthals ultimately became extinct. “The combination of DNA analysis and age dating has revealed that a sharp decline in population size began around 45,000 years ago,” says Thorsten Uthmeier. It is still unclear exactly what led to their extinction about 3,000 years later. In addition to significant differences in the size and density of social networks, it is possible that parts of the last Neanderthal population were absorbed by groups of Homo sapiens sapiens, who, having come from Africa, spread across increasingly larger areas of Europe. Uthmeier: “Modern humans and Neanderthals were capable of interbreeding, which is why we still carry a small percent of Neanderthal DNA in us today.”

*DOI: 10.1073/pnas.2520565123

“Archaeogenetic insights into the demographic history of Late Neanderthals”

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