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The rib cage of Neanderthal infants, similar to that of adults, was genetically determined and was not the result of development, according to a research led by Spaniards.
According to the study, this conditioning would have an evolutionary meaning, since it would have been "inherited" from previous species such asHomo erectus.
Genetic determination implies that the differences between the different human species are already present from thebirth, being accentuated only a little during the growth of its individuals.
This would explain, for example, that Neanderthal infants (Homo neanderthalensis) present a thorax with a different shape to the modern rib cage typical of theHomo sapiens.
However, the similarities of Neanderthals with respect to the shape and development of the thorax of other species, such asHomo erectus, hypothesizes that hissquat physiognomy It was not only the result of a genetic inheritance transmitted from parents to children, but it could be inherited at the evolutionary level.
Compared to the thorax of modern humans, the thorax of adult Neanderthals was shorter, slightly deeper, and much wider. These anatomical characteristics are related to its wide pelvic body, robust bones and great musculature.
It would also be related to the demands of themetabolism of these hunter-gatherers, who needed a lot of energy and oxygen. But until now it was unknown if these differences were established at birth, that is, they were genetic, or appeared later during their development.
A study, led by the National Museum of Natural Sciences (MNCN-CSIC) and the National Center for Research on Human Evolution (CENIEH), shows thatneanderthals Newborns had a rib cage similar to that of an adult, capable of sustaining the high energy expenditure of a large and broad body.
This implies that the shape of thechest Neanderthal would be genetically determined and would not be the result of development, which would have a high evolutionary significance as it is “inherited” from previous species such asHomo erectus. The study is published in the journalScience Advances.
3D reconstructions of the Neanderthal thorax
To prove,Daniel Garcia-Martinez, lead author of the study and paleontologist at CENIEH, together with an international team of experts, usedvirtual reconstruction and traditional and geometric morphometry to reproduce, for the first time, the shape of the thorax of four Neanderthal individuals.
These reconstructions, which come from Neanderthals from three countries, show their evolution from birth (one or two weeks old) to three or four years: Mezmaiskaya 1 (Russia), Le Moustier 2 (France), Dederiyeh 1 (Kurdistan Sirio) and Roc de Marsal (France).
“Our results indicate that the rib cage of Neanderthal newborns was already different from our species. This is observed in that they were deeper, shorter and wider than those of modern humans, as can also be seen in adults ”, says the researcher.
"At the time of birth, Neanderthals already had different brains and jaws, so it makes sense that the morphology of the thorax was also genetically determined and was found in newborns", say professors Christoph Zollikofer and Marcia Ponce de León, co-authors from the University of Zurich, Switzerland.
This research has required a great deal of work to identify and organize the different elements of the thorax of Neanderthal children and newborns because “the ribs and vertebrae normally appear very fragmented in the fossil record, which has traditionally made their study ”, explainsAsier Gómez-Olivencia, co-author of the article from the University of the Basque Country.
A trait shared by other humans
In addition, the scientist puts in evidence that this form of the rib cage could not be exclusive to Neanderthals, since it is also observed in other previous species.
“This morphology represents the archaic condition shared withHomo erectus, and it is probably related to high energy requirements, since infant Neanderthals also have a large nasal opening, "he says.Markus Bastir, second author and researcher at the National Museum of Natural Sciences of Madrid (MNCN-CSIC).
This study lays the foundations on the shape of the Neanderthal thorax at birth, and represents the continuation of the work on the evolution of the rib cage that this team has been carrying out for years, in collaboration with different European institutions.
“Although we have been researching the Neanderthal thorax for years and there is a general consensus in the scientific community in this regard, there is still a long way to go in the study of the evolution of the human thorax, since very little is known about this very central element of the body of other previous species of the genus Homo ”, concludes Daniel García-Martínez.
D. García-Martínez et al. "Early development of the Neanderthal ribcage reveals a different body shape at birth compared to modern humans” Science Advances October 7, 2020.