A collaborative international research initiative has identified a significant demographic collapse affecting Neanderthal populations, commencing approximately 75,000 years ago.
Although they experienced a period of recovery, the vast majority of late-era Neanderthals in Europe were found to be progeny of a solitary, diminutive ancestral group.
This diminished genetic variability is posited as a potential contributing factor to their ultimate demise, which occurred around 40,000 years ago.
“We possess evidence indicating that Neanderthals populated Europe without interruption from 400,000 to 40,000 years ago,” stated Cosimo Posth, a paleogeneticist affiliated with the University of Tübingen in Germany.
“Nonetheless, our understanding of their population dynamics remains fragmented, with limited insight into the evolutionary trajectories that preceded their extinction.”
To elucidate these historical events, the investigators in the current investigation integrated genetic analysis with extant archaeological findings. Their findings suggest that circa 75,000 years ago, glacial conditions likely compelled dispersed Neanderthal communities to seek refuge in a singular, secure locale, or refugium, believed to be situated in what is now southwestern France.
The European late Neanderthals examined in this study inhabited the period between 60,000 and 40,000 years ago. The research team meticulously analyzed the mitochondrial DNA (mtDNA), inherited exclusively through the maternal line, extracted from osseous and dental remains of 59 distinct Neanderthal individuals.
While mtDNA does not encompass the entirety of the nuclear genome, it exhibits superior preservation capabilities in ancient environmental conditions over millennia. Furthermore, its extraction from fossilized remains, as was executed in this research, is comparatively more facile.
Through a comprehensive statistical assessment of the mtDNA data, the researchers were able to identify a period around 65,000 years ago as the epoch when the population’s genetic makeup began to exhibit substantial renewed diversification – coinciding roughly with the timeframe when Neanderthals may have been able to re-emerge from their Ice Age sanctuary.
Despite the wide geographical distribution from which the mtDNA samples were procured, a singular dominant maternal lineage was consistently identified across all samples, strongly suggesting a common ancestry originating from an unexpectedly confined group of individuals.
“This finding elucidates why virtually all late Neanderthals whose genomes have been sequenced to date – spanning from the Iberian Peninsula to the Caucasus region – are affiliated with the identical line of inherited mitochondrial DNA,” commented Posth.
However, this period of stability was not perpetual. The mtDNA analysis also revealed a precipitous and abrupt contraction in Neanderthal genetic diversity between 45,000 and 42,000 years ago.
This observation serves as definitive evidence of a significant and rapid reduction in population size preceding their ultimate extinction, estimated to have occurred around 40,000 years ago.
Such a pattern strongly indicates a species prone to repeated episodes of dispersal and fragmentation into smaller, isolated communities. These fragmentations would have rendered them more susceptible to environmental adversities, ecological pressures, and the inherent risks associated with limited genetic diversity, including heightened vulnerability to disease and deleterious mutations.
While the reconstruction of this timeline necessitates certain inferential leaps, and acknowledging that mtDNA analysis does not offer the complete genetic panorama provided by full genomic sequencing, the study presents a highly persuasive argument.
Consequently, it suggests a departure from the notion of a linear progression in European Neanderthal ancestry. Instead, the narrative derived from this research depicts a sequence of contraction, subsequent expansion, a significant decline, and ultimately, complete extinction.
This research further underscores the efficacy of integrating diverse analytical approaches within a single study. In this instance, the synergistic combination of mtDNA data and a broader collection of archaeological records, detailing the migratory patterns of Neanderthal populations over time, has proven instrumental in constructing a meaningful reconstruction of ancient history.
“This integrated methodology permitted us to meld both evidentiary streams and reconstruct the demographic trajectory of Neanderthals across both spatial and temporal dimensions,” explained Jesper Borre Pedersen, a paleolithic archaeologist from the University of Tübingen.
