Researchers uncovered that the genetic diversity of the Neanderthals is larger then previously thought. Moreover, the findings suggest that the genetic diversity may have been higher in earlier Neanderthal periods relative to later periods that approached the arrival of humans in Europe.

This might prove to be highly relevant because changes in genetic diversity over time reflect population events, such as low-population bottlenecks caused by disease or environmental change, as well as the influence of random genetic change.

Neanderthals were the only representatives of the genus Homo in Europe during most of the last 300,000 years, becoming extinct shortly after the arrival of modern humans on the continent around 30,000 years ago. Traces of mitochondrial DNA (mtDNA) sequences still present in fossilized bones have been used in past studies in an effort to identify and track the potential genetic legacy of Neanderthals among modern Europeans. Though such genetic continuity would have been the hallmark of interbreeding between modern humans and Neanderthals at the time of their European coexistence, the mtDNA sequences from the nine Neanderthal specimens that have been analyzed to date - and that lived around the time of the cohabitation period - do not match those found among modern humans, suggesting that little, if any, interbreeding took place.

In their new work, Dr. Catherine Hänni and colleagues now report the oldest Neanderthal mtDNA sequence ever recovered. The Neanderthal specimen analyzed consists in a molar of a 10-12 year-old child that lived in the Meuse valley (Scladina cave, Belgium) around 100,000 years ago.

The reason for choosing such an old specimen was simple: it unambiguously predates the period when Neanderthals cohabited with modern humans. By comparing this sequence with already published - and considerably younger - Neanderthal sequences, the researchers sought to reveal whether the Neanderthal mtDNA pool exhibited long-term stability or drastic modification around the time of cohabitation with modern humans.

A second reason to pay attention to the Scladina molar is that it has only been discovered very recently. This means that all individuals who have been in contact with it are known, and their DNA could be sequenced to detect any possible contamination of the Neanderthal sample by modern human DNA.

The Neanderthal sequence from Scladina confirms that Neanderthals and modern humans were only distant relatives - Neanderthal sequences are all closer to each other than to any known human sequence.

But the study also reveals that the genetic diversity of Neanderthals has been underestimated. Indeed, the mtDNA from the Scladina sample is more divergent relative to modern humans than is mtDNA from recent Neanderthals, suggesting that Neanderthals were a more genetically diverse group than previously thought. Because this diversity is higher in earlier Neanderthals than in later Neanderthals, it also suggests that their disappearance after the encounter with modern humans may not be exclusively due to modern humans - some other factors may have played a role in their demise.

Photo credit: G. Focant, Ministere de la Region Wallonne, Belgium. Publishing in the June 6th, 2006 Current Biology.