A Long-Standing Mystery in Human Evolution
The disappearance of Neanderthals remains one of the most debated topics in paleoanthropology. Theories have ranged from climate shifts to competition with modern humans, but new research suggests that a severe decline in genetic diversity may have played a crucial role in their extinction.
A Unique Approach to Understanding Neanderthal Genetics
The researchers analyzed several different bottleneck scenarios. (Urciuoli et al., Nature Communications, 2025)
An international team of researchers has provided compelling evidence that a genetic bottleneck—an event where a population's genetic diversity drastically declines—occurred over 100,000 years ago. Their study combined fossil analysis with genetic data, focusing on the shape of the inner ear’s semicircular canal as a marker of genetic variation.
By comparing ear canal structures in Neanderthal fossils from various regions across Europe and western Asia with those of modern humans, the researchers could assess differences in genetic diversity over time.
Evidence of a Population Decline
Ear semicircular canal shapes were studied in fossils from several sites across Eurasia. (Urciuoli et al., Nature Communications, 2025)
Key fossil sites played a vital role in the study. Neanderthal remains from Krapina, Croatia—dating back 130,000 years—were compared with later Neanderthal fossils from France, Belgium, and Israel, which date between 41,000 and 64,000 years ago. The findings indicate a significant reduction in genetic diversity between these two time periods, suggesting a dramatic population decline well before Neanderthals ultimately vanished around 40,000 years ago.
While the study does not pinpoint the exact cause of this genetic crisis, previous research has suggested possible factors such as environmental changes, food scarcity, or intensified competition with other human groups.
New Questions About Neanderthal Evolution
Despite offering strong evidence of a late-stage genetic bottleneck, the study also challenges earlier assumptions. The fossils from Krapina exhibited an unexpectedly high level of genetic diversity, similar to samples dating back as far as 430,000 years. This contradicts theories of an earlier genetic crisis shaping Neanderthal evolution and instead supports the idea that a single, later population collapse played a more direct role in their extinction.
Expanding the Research
The researchers plan to apply this method of ear structure analysis to a broader range of fossils and locations. This could shed further light on Neanderthal migration patterns, population dynamics, and the factors that ultimately led to their demise.
"This study presents an innovative approach to estimating genetic diversity in Neanderthal populations," says anthropologist Rolf Quam from Binghamton University. As more fossils are analyzed, researchers hope to gain an even clearer picture of how our ancient relatives lived—and why they disappeared.
