Studying sinuses to understand human evolution

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Éstudying sinuses to understand human evolution

View of the skull and sinuses of specimen D4500, attributed to Homo erectus or Homo georgicus.

Paleoanthropologists have performed the first major study of the sinuses of most human species and large primates, to help understand human evolution.

The frontal sinuses participate in the physiological balance of the face, in connection with breathing, explains to AFP Antoine Balzeau, paleoanthropologist at the National Museum of Natural History. But the origin and evolution of these cavities located above the nasal septum, very close to the brain, remains largely a mystery.

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Diagram summarizing the variations observed for the frontal sinuses during human evolution.

The study published in the journal Science Advances is the first to identify the position, shape and size of the sinuses of more than sixty specimens and not far from twenty species, underlines Mr. Balzeau, its main author.

The exceptional cooperation of a large international team, unusual in anthropology – a field where institutions holding fossils are often reluctant to share the study – has made it possible to obtain scanners of almost all human fossils, says the scientist.

In addition, the study establishes for the first time a very clear distinction between two large groups. In the great apes (chimpanzees, bonobos and gorillas), but also the first species of the human line, from Sahelanthropus tchadensis(Toumaï) to Australopithecines (Lucy) and Paranthropes, the size of the frontal sinuses is directly linked to that of their cranial box.

Everything changes for the human line with the genus Homo, including Homo erectus, around 2 million years ago.

The increase in the size of the skull of species of the genus Homothen sees the sinuses in general becoming smaller relative to the size of the skull and more constrained by the shape of the face, Balzeau says. Added to this are strong variations even within the same species, and particularly for Homo sapiens.

This diversity calls into question many hypotheses, such as the one attributing to Neanderthal large sinuses, supposed to have favored his adaptation to a cold climate. The study thus shows that in sapiens, it is not the climatic factor that seems to influence the size of the frontal sinuses, according to him. It didn't happen in Homo sapiens, so there's no reason it happened in Neanderthals, according to Mr. Balzeau.

The study brings a new angle to the description of the particularities of human groups. “And raises the question of the classification of three specimens for the moment unclassifiable of the genus Homo (Petralona, ​​Bodo and Broken Hill) endowed with gigantic sinuses, a hyperparticular thing, remarks Mr. Balzeau, whose work may one day help determine what species they belonged to.

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