A fossil site in Spain has turned up some astonishing results: mitochondrial DNA from hominins that lived 400,000 years ago. The DNA suggests they were related to the Denisovans; an extinct hominin group that was recently shown to have interbred with Neanderthals and modern humans. The results of the study were published this week in Nature from lead author Matthias Meyer from the Department of Evolutionary Genetics at the Max Planck Institute for Evolutionary Anthropology.

The Sima de los Huesos is a cave fossil site in Spain that has been studied and excavated over the last 20 years. So far nearly 30 skeletons have been recovered from the site, all of which are at least 300,000 years old. They are tentatively classified as Homo heidelbergensis, though there are distinct physiological similarities to Neanderthals. Popularly, they are being referred to as the Sima hominins. Thanks to advances in sequencing technology, the researchers were able to recover a near-complete mitochondrial genome to learn more about our ancient relatives.

The recovered DNA came from a 400,000 year old femur recovered by a team of Spanish scientists. Meyer’s team of German geneticists used special techniques to restore the damaged mtDNA. The resulting sequence gave the researchers a few surprises as it revealed ancient secrets about hominin evolution. This is one of the oldest genomes ever recovered; which is doubly impressive since these bones were not preserved through permafrost.

The bones recovered from Sima look somewhat similar to Neanderthals, but their mtDNA shows they are more closely related to Denisovans. This raises questions about the evolutionary relationships between these groups. The Sima remains were from a population that may have been ancestral to Neanderthals and Denisovans or there could have been a yet-unknown group that caused the shared genetic information.

The success of finding the code for such old mtDNA opens the door for genomes of other ancient fossils to be sequenced. Future research will also try to obtain mtDNA from other individuals at the Sima site, as well as trying to recover nuclear DNA which reveal many secrets of the lives of this extinct human population.