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.

The study published in 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 that hold fossils are often reluctant to share the study - has made it possible to obtain the scanners of "almost all human fossils", indicates the scientist.

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 the australopithecines (Lucy) and paranthropes, the size of the frontal sinuses is directly linked to that of their brains.

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

The increase in the size of the skull of species in the genus Homo then sees "the sinuses in general becoming smaller in relation to the size of the skull and more constrained by the shape of the face", says Balzeau.

Added to this are strong variations, including within the same species, and particularly for Homo sapiens, the ancestor of modern man.

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 touch 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 hyper-particular thing", remarks Mr. Balzeau, whose work will perhaps help to be one day figuring out what species they belonged to.

© 2022 AFP