Professor Juan Alberto Sanchis Gimeno, from the Department of Human Anatomy and Embryology of the Faculty of Medicine and Dentistry of the Universitat de València; the National Museum of Natural Sciences (MNCN-CSIC), and the National Centre for Research on Human Evolution (CENIEH) have participated in the study. Three vertebrae from the Krapina site (Croatia) have been analysed and material from other sites has been reviewed.

Neanderthals inhabited the European continent until barely 30,000 years ago and their disappearance remains a mystery. In order to know their genetic diversity, work has been done to decipher their genome, but also to analyze different anatomical characteristics of the fossil record of the species. "In this study we have focused on the anatomical variants of the first cervical vertebra, known as the atlas. The anatomical variants of this vertebra have a high relationship with genetic diversity: the higher the prevalence of this type of anatomical variants, the lower the population genetic diversity", explains MNCN researcher Carlos A. Palancar.

In Homo sapiens the anatomical variants of the atlas have been widely studied in recent years. In the case of modern humans, the atlas shows some of the different anatomical variants in almost 30% of cases. "However, probably due to the poor preservation of this cervical vertebra and the little material recovered in the fossil record, the atlas of Neanderthals have hardly been observed under this magnifying glass," says Juan Alberto Sanchis Gimeno, a researcher at the Universitat de València.

Recently, researchers from the MNCN Paleonanthropology Group determined the presence of different anatomical variants in the atlases of the Neandertals from the El Sidrón site (Asturias). In order to confirm the high prevalence of anatomical variants of this species, they thoroughly analyzed the fossil atlases of the Neandertals from the Krapina site (Croatia). "Krapina is a site of about 130,000 years old, compared to about 50,000 years old in El Sidrón. It is the site from which the largest number of Neanderthal remains have been recovered, which makes it a sample of special interest in the analysis of the genetic diversity of this species since potentially all the individuals belonged to the same population," points out Daniel García-Martínez, researcher at the CENIEH.

The study of the anatomy of the three atlases recovered in this site has revealed the presence of anatomical variants in two of them (66%). One of them, known as Unclosed Transverse Foramen, UTF, has a prevalence of only 10% in modern humans. "Checking the presence of these anatomical variants in Krapina, together with the review of other atlases presented to the scientific community that have not been analyzed under this perspective until now and that yield similar data (more than 50%), suggests that the number of variants in Neanderthals is significantly higher than that of current humans," says Palancar.

"These data support the theory that their genetic diversity was very low and confirm that this could be one of the causes of their disappearance," concludes MNCN researcher Markus Bastir.