José Mª Bermúdez de Castro, Adrián Pablos and Nohemi Sala, from Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), are members of the Spanish research team that has participated in a paper published today in the journal Science on the recovery of nuclear DNA from several Neanderthal individuals, from the sediment of two Siberian caves and the Galería de las Estatuas, in the Cueva Mayor of the Sierra de Atapuerca (Burgos, Spain).

This publication, led by Benjamin Vernot, of the team of Matthias Meyer, senior researcher in the evolutionary genetics group at the Max Planck Institute for Evolutionary Anthropology in Germany, can certainly be characterized as historic, because it opens a whole new avenue to future research. “Human fossils will no longer be necessary to identify the inhabitants of a prehistoric cave”, affirm the authors.

In the excavations, led by Juan Luis Arsuaga, scientific director at the Museo de la Evolución Humana (MEH), which have been under way in the Galería de las Estatuas since 2008, the remains of animals consumed by Neanderthals and their stone tools have been recovered, in addition to a foot phalanx which is indisputably Neanderthal. Due to their complete isolation, the sediments of this site have remained under constant conditions of humidity and temperature, and have not undergone any alteration by natural agents or interventions by modern humans.

The Atapuerca research team, to which the CENIEH researchers belong, is engaged in a long-standing collaboration with Meyer which has produced spectacular results at the Sima de los Huesos site, also in the Cueva Mayor, with the recovery of more ancient human mitochondrial and nuclear DNA, although from fossils.

Human fossils will no longer be necessary to identify the inhabitants of a prehistoric cave

Recently, the team directed by Meyer has explored the possibility of obtaining DNA directly from sediments, avoiding the need to take samples from human bones, which are absent from most sites. It was shown in an earlier paper that it was possible to recover mitochondrial DNA from sediments, but this had not been achieved for nuclear DNA.

The temperature is a primordial factor in the conservation of the DNA molecule: the higher the temperature, the more the molecule degrades. Therefore, the further north the site, the better the conservation will be. Siberia is the ideal place for recovering ancient DNA but the special characteristics of the Galería de las Estatuas offered a unique opportunity to obtain DNA from sediment in a region situated in more temperate latitudes.

The Neanderthals of Estatuas

In the Galería de las Estatuas sediments, both nuclear DNA and mitochondrial DNA from several individuals have been recovered. The DNA of the oldest individual belonged to a Neanderthal man of an ancient line. It has been dated to around 110,000 years old, but this lineage arose earlier, about 130,000 years ago.

The date which has been calculated for this “radiation”, namely, the array of lines which emanate from a common ancestor, coincides with the start of the last warm period between two glaciations. The radiation and the improved climate could be linked, because major environmental changes yield major ecological changes, which affect the evolution of many species.

Some thousands of years later, the Neanderthal population of Galería de las Estatuas was genetically different, and associated to a second radiation. Along the stratigraphic sequence, DNA has been identified from at least four women belonging to these newer Neanderthals, who had superseded the old ones. The most modern have been dated to about 80,000 years old. By then, the climate had changed, because the last glacial cycle had already commenced. Once again, the relationship between climate and human evolution is very intriguing.

Neanderthals from the last glaciation are known informally as “classic”. They are the best-studied and are also the ones presenting the most exaggerated traits. In addition, the "classic" Neanderthals have one highly important characteristic: they had the largest brains in the whole course of human evolution, outstripping even our own.