400,000-year-old fossils from Spain have been revealed to belong to the earliest relatives of Neanderthals ever found.
Previous analyses of the hominins from Sima de los Huesos in 2013 showed that their maternally inherited mitochondrial DNA was distantly related to Denisovans, extinct relatives of Neanderthals in Asia. This was unexpected since their skeletal remains carry Neanderthal-derived features.
Researchers of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have since worked on sequencing nuclear DNA from fossils from the cave, a challenging task as the extremely old DNA is degraded to very short fragments.
The results now show that the Sima de los Huesos hominins were indeed early Neanderthals. Neanderthals may have acquired different mitochondrial genomes later, perhaps as the result of gene flow from Africa.
Until now it has been unclear how the 28 400,000-year-old individuals found at the Sima de los Huesos aka "pit of bones" site in Northern Spain were related to Neanderthals and Denisovans who lived until about 40,000 years ago.
"Sima de los Huesos is currently the only non-permafrost site that allows us to study DNA sequences from the Middle Pleistocene, the time period preceding 125,000 years ago," said lead author Matthias Meyer.
Meyer added, "The recovery of a small part of the nuclear genome from the Sima de los Huesos hominins is not just the result of our continuous efforts in pushing for more sensitive sample isolation and genome sequencing technologies. This work would have been much more difficult without the special care that was taken during excavation."
The study is published in Nature.