First cervical vertebra, called the atlas, where the congenital anomaly were observed. / Communication CSIC
The Neanderthals lived in small groups, isolated and relatively low genetic diversity, according to a new analysis of skeletal remains found in the cave of El Sidrón (Asturias ). The work, led by the Higher Council for Scientific Research (CSIC) and published in the journal PLoS ONE points to the high incidence of birth defects in the first cervical vertebra , called Atlas, along with the retention of canine teeth, may be the result of inbreeding in the group of Neanderthals who lived in that cave.
“Congenital anomalies have been found in two of the three atlas recovered at the site of The Sidrón, a group consisting of a total of 13 Neanderthals, “says Antonio Rosas, director of the study and researcher at the CSIC at the National Museum of Natural Sciences (MNCN).
According to the researcher,” the atlas bone forms a ring which rests the skull, and can have a variety of congenital anomalies of low frequency in the front and back of the ring. ” Among these abnormalities, “the simplest is dehiscence (lack of closure) of the posterior arch in the median line, which current human populations occurs with low frequency, ranging from 1% to 4%,” explains Rosas.
“In clinical practice, the discovery of this defect Atlas is casual in most cases, and is often caused by medical imaging tests (X-rays, CT axial) requested by example by trauma to the cervical region, “says Luis Rios, first author of the paper and scientist MNCN.
” One of the atlas of the Sidrón presents this defect. The second atlas presents a dehiscence of the anterior arch also in the median line. This is a defect that occurs much less frequently, below the 0.1% in modern human populations, “says the researcher.
Three possible explanations
How the presence of two of these congenital anomalies of low frequency in a Neanderthal as small group explained? “There are three possible explanations,” says Antonio Rosas. The first is that this congenital abnormality has a genetic basis and the high frequency indicates that these two individuals are familiar Neanderthals. This interpretation marries genetic studies in the Sidrón, where family relationships between individuals in the group are deducted.
The second explanation It is superimposed on the first, and aims to inbreeding or “practice of marrying persons of common or natural heritage of a small town or region”, as defined by the SAR. Indeed, the demographic scenario drawn to Pleistocene human groups is small and scattered, which would favor the pairing within the group and consequently, long-term, within the same family.
“Over time, inbreeding can lead to an increase in the frequency of small variations and congenital skeletal abnormalities (as transposed teeth, spinal defects such as dehiscence of the atlas, cervical ribs) and a higher frequency of these anomalies has been observed for example in island or human populations located in isolated areas, “explains Rios. Even in conservation biology these anomalies can be used as indicators of inbreeding in areas of repopulation of wildlife.
On the other hand, recent genetic studies on samples from El Sidrón, Vindija (Croatia) and Siberia (Russia), would point to a common match between Neanderthals with close kinship relations, and congenital anomalies of the atlas in the Sidrón could be interpreted as another sign, in this case skeleton, inbreeding Neanderthals in this geographical area.
Together, “the demographic picture of Neanderthals groups clarified in recent years can give a biological explanation for the numerical decline of their populations, which over time could have led to its final extinction, “said Rosas.
A third explanation linking possible congenital deficiencies (eg, defects in neural tube closure ) with adverse environmental conditions during the early periods of gestation, such as a power pattern deficient in some nutrients. Although the accumulation of genetic data and osteological signals a demographic scenario of inbreeding, the testing of this hypothesis will only further studies of Neanderthal remains, the researchers conclude.
Original article here
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