An archaic hominin femur from southwestern Germany is found to carry mitochondrial DNA (mtDNA) that splits from other Neanderthals around 270,000 years ago. The findings, published in Nature Communications, refine time boundaries for African gene flow into Neanderthals.
Analyses of nuclear DNA predict that modern humans diverged from Neanderthals and Denisovans 765,000-550,000 years ago, whereas mtDNA shows a closer relationship between modern humans and Neanderthals. Although a genetic introgression event (the introduction of genes from one species into another species) from African hominins into the early Neanderthal has been invoked to explain this discrepancy, uncertainty still exists due to scarcity of fossils.
Cosimo Posth, Johannes Krause and colleagues reconstruct the complete mtDNA genome of an archaic femur from the Hohlenstein-Stadel cave in southwestern Germany. This sample represents the deepest diverging lineage among Neanderthal mtDNAs discovered to date. This discovery suggests that Late Pleistocene Neanderthal mtDNAs originated through gene flow from an African source more than 270,000 years ago, which might have replaced earlier Denisovan-like mtDNA lineages. These findings provide new insights into the evolution of Neanderthals, although the authors note that an analysis of nuclear DNA might offer more information on the genomic relationships between Neanderthals, Denisovans and modern humans; however, the nuclear DNA from the German archaic femur is poorly preserved, making it difficult to retrieve its complete genome.