The Reclusive Neanderthals

Neanderthals (Homo neanderthalensis) were an extinct species within the genus Homo. Because Neanderthals lived in Eurasia during a period when they overlapped geographically with modern humans (Homo sapiens), and because they possessed sophisticated technologies, cultural traditions, and even exchanged genes with modern humans, they have long remained a central subject of archaeological and paleoanthropological research.

For many years, scientists have proposed numerous hypotheses to explain the disappearance of Neanderthals. These explanations often emphasize environmental forces such as climatic fluctuations, volcanic eruptions, or even geomagnetic reversals. Such interpretations generally imply that Neanderthal extinction was primarily driven by external ecological events rather than by biological or cultural characteristics intrinsic to Neanderthal populations themselves. This emphasis on environmental explanations partly reflects the fact that internal factors—such as Neanderthal social organization, historical dynamics, and behavioral structures—have remained comparatively understudied.

Nevertheless, archaeological and genomic evidence has revealed certain patterns in Neanderthal population structure. Studies of Neanderthals from Siberia and late European contexts have indicated relatively small effective population sizes and signs of inbreeding. These findings suggest that Neanderthal groups may have consisted of small communities with limited movement and interaction between groups. In contrast, early modern human populations in Eurasia, although also small in size, appear to have experienced lower levels of inbreeding and greater intergroup mobility. Whether these observations represent a universal feature of Neanderthal societies, however, remains uncertain.

Thorin's discovery location and fossil distribution, along with the discovery sites of other Neanderthal fossils whose genomes were used in this study（圖片來源：Slimak, L et al. ，採用 CC BY-NC 4.0 授權。）

A study published in 2024 analyzed the genome of a Neanderthal individual discovered in 2015 at Grotte Mandrin, a site located along the Mediterranean coast of southern France. The individual, nicknamed “Thorin,” provides an important new perspective on Neanderthal extinction through the lens of gene flow and population structure.

At the time the study was conducted, Thorin's remains were still undergoing excavation. Nevertheless, several recovered elements—including teeth and finger bones—displayed morphological features characteristic of Neanderthals. These remains confirmed that the individual belonged to the Neanderthal lineage.

Radiometric dating and stratigraphic analyses initially placed Thorin within a time range of approximately 52,900 to 48,050 years ago. However, because the excavation was ongoing and the precise stratigraphic context could still change—particularly if the individual had been intentionally buried—the most conservative estimate places Thorin's age between about 52,900 and 42,000 years ago.

The Thorin jaw specimen and its reconstruction（圖片來源：Slimak, L et al. ，採用 CC BY-NC 4.0 授權。）

Isotopic analyses of Thorin's teeth, examining carbon, nitrogen, oxygen, and strontium ratios, indicate that he lived in a cold and open environment. These environmental signals are consistent with the climatic conditions inferred from the surrounding sediments, reinforcing the reliability of the chronological estimates.

Researchers extracted DNA from the root of Thorin's first molar and compared the genome with those of other Neanderthal individuals. Genetic analysis showed that Thorin was male. Surprisingly, molecular estimates initially suggested that his lineage dated back roughly 100,000 years, a figure about 50,000 years older than the archaeological dating suggested.

Further analyses resolved this discrepancy. The results indicated that Thorin's lineage diverged from other Neanderthal populations approximately 100,000 years ago. After this divergence, the population to which Thorin belonged appears to have remained genetically isolated for roughly 50,000 years. During that time, there was no detectable gene flow between Thorin's population and other known Neanderthal groups.

This isolation is particularly striking given that geographically neighboring Neanderthal populations lived relatively nearby. In fact, some of these groups were close enough that the distance between them could have been covered on foot in roughly ten days. Despite this proximity, genetic data show no evidence of interbreeding or sustained contact between them. This prolonged isolation explains why Thorin's lineage appears genetically ancient compared with other late Neanderthals.

The study also revealed another asymmetry in gene flow. Late Neanderthal genomes show no evidence of recent genetic contributions from modern humans, whereas modern human populations outside Africa carry small proportions of Neanderthal DNA. This pattern suggests that genetic exchange between the two groups was not reciprocal. Such asymmetry may reflect social structures within Neanderthal populations that limited interaction not only with modern humans but also between different Neanderthal groups.

Neanderthal（（圖片來源：Homo sapiens neanderthalensis-Jäger, Neanderthal Museum ，採用 CC BY-SA 4.0 授權。）

Overall, the genomic evidence indicates that Neanderthal populations often consisted of small, isolated communities with minimal interaction between them. In contrast, early modern humans entering Europe appear to have maintained broader social networks and greater connectivity between groups.

These contrasting social structures may have had profound consequences. Long-isolated Neanderthal groups likely faced increasing vulnerability when encountering modern human populations characterized by larger and more interconnected social systems. Rather than a single catastrophic event, the disappearance of Neanderthals may therefore have been the result of a complex and gradual process. Within that process, the social organization and behavioral patterns of Neanderthal populations themselves may have played an important role.

Author: Bai Leng

Reference:

Slimak, L., Vimala, T., Seguin-Orlando, A., Metz, L., Zanolli, C., Joannes-Boyau, R., Frouin, M., Arnold, L. J., Demuro, M., Devièse, T., Comeskey, D., Buckley, M., Camus, H., Muth, X., Lewis, J. E., Bocherens, H., Yvorra, P., Tenailleau, C., Duployer, B., Coqueugniot, H., Dutour, O., Higham, T., Sikora, M. (2024). Long genetic and social isolation in Neanderthals before their extinction. Cell Genomics.