Australia: The Land Where Time Began

A biography of the Australian continent 

Neanderthal Group Low Genetic Diversity in the El Sidrón, Asturias, Spain, Congenital Clefts of the Atlas, Possible Further Evidence of Low Genetic Diversity

In this paper Ríos et al. present evidence of the first cases in Neanderthals of congenital clefts of the arch of the atlas. They found that 2 atlases that were recovered from El Sidrón, in Spain that have a defect in the posterior arch, which has a frequency of 0.73 %-3.84 % in modern human populations, and an anterior arch, that has a frequency in modern human populations of 0.087 %-0.1 %, which is a condition that in most cases is not associated with any clinical manifestation. 2 of the 3 observable atlases from this site had a congenital condition that was otherwise a low frequency abnormality, together with evidence that had previously been reported of 2 out of 10 individuals from this site having deciduous mandibular canines that were retained, support observations that were made previously that at this site the Neanderthals constituted a group with close genetic relations. It has been proposed that skeletal congenital conditions in humans and other species, although these conditions are without clinical significance, could be used as a signal of endogamy or inbreeding. In the case of the Neanderthals from this site Ríos et al. say this interpretation would fit the general scenario in which a high incidence of a rare conditions among humans in the Pleistocene and the specific scenario that emerges from Neanderthal palaeogenetics, which indicates there was a long-term small and decreasing population size with reduced and isolated groups. An alternative, non-exclusive explanation for such as high incidence of congenital conditions could possibly be adverse environmental factors that affected early pregnancies. According to Ríos et al. further support or rejection of these interpretations will come from new genetic and skeletal studies of Neanderthals remains.

Conclusion

According to Ríos et al. this study on Neanderthals involved the first 2 cases in which a congenital posterior and congenital anterior cleft of the arch of the atlas respectively. Together with the dental anomalies in 2 individuals from the same site that was reported previously, these observations could be interpreted as further evidence of the presence of a group with close genetic relations at El Sidrón, as a possible signal of inbreeding in the group of Neanderthals, and as an indicator of environmental conditions that were harsh. Ríos et al. suggest previous findings of a high incidence among humans of the Pleistocene of conditions that are considered to be rare, and the general demographic scenario that involved inbreeding, for Neanderthals that has emerged from palaeogenetics would be compatible with an explanation of the presence of these low frequency atlas clefts in 2 of the 3 atlases from El Sidrón that were observable. New genetic and skeletal evidence from Neanderthal remains should either support or reject these findings.

Sources & Further reading

Ríos, L., A. Rosas, A. Estalrrich, A. García-Tabernero, M. Bastir, R. Huguet, F. Pastor, J. A. Sanchís-Gimeno and M. de la Rasilla (2015). "Possible Further Evidence of Low Genetic Diversity in the El Sidrón (Asturias, Spain) Neandertal Group: Congenital Clefts of the Atlas." PLoS ONE 10(9): e0136550.