Another ancient genome, another mystery. DNA gleaned from a 400,000-year-old femur from Spain has revealed an unexpected link between Europe’s hominin inhabitants of the time and a cryptic population, the Denisovans, who are known to have lived much more recently in southwestern Siberia.
The DNA, which represents the oldest hominin sequence yet published, has left researchers baffled because most of them believed that the bones would be more closely linked to Neanderthals than to Denisovans. “That’s not what I would have expected; that’s not what anyone would have expected,” says Chris Stringer, a palaeoanthropologist at London’s Natural History Museum who was not involved in sequencing the femur DNA.
The fossil was excavated in the 1990s from a deep cave in a well-studied site in northern Spain called Sima de los Huesos (‘pit of bones’). This femur and the remains of more than two dozen other hominins found at the site have previously been attributed either to early forms of Neanderthals, who lived in Europe until about 30,000 years ago, or to Homo heidelbergensis, a loosely defined hominin population that gave rise to Neanderthals in Europe and possibly humans in Africa.
But a closer link to Neanderthals than to Denisovans was not what was discovered by the team led by Svante Pääbo, a molecular geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
The team sequenced most of the femur’s mitochondrial genome, which is made up of DNA from the cell’s energy-producing structures and passed down the maternal line. The resulting phylogenetic analysis — which shows branches in evolutionary history — placed the DNA closer to that of Denisovans than to Neanderthals or modern humans. “This really raises more questions than it answers,” Pääbo says.
In retrospect, we ought to have seen this coming. EVERYTHING with people is messy and complicated. ;)
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