The human skull is full of holes and cavities with very different sizes and functions. Some of them, the largest, serve to house the brain and cerebellum and on others, the maxillary sinuses, just thin bony walls, our faces sit. But there is more. Just above the nose bones and near the eye sockets are the so-called frontal sinuses, those that are filled with mucus when we suffer from sinusitis. For decades, scientists have debated what the exact function of these small cranial cavities of just a few centimeters might be. Insulate the frontal lobe from the cold outside? Do they have to do with the mechanics of chewing? Or perhaps with the morphological characteristics of the brain? What is known is that the frontal sinuses affect brain size and shape. In fact, whether these holes are more or less large influences the dimensions of our frontal lobe.
But there is also another mystery. In different human species, the size of the frontal sinuses varies, it is not the same. In the neanderthals, for example, these cavities are larger than in our own species. And although there are several theories that have tried to explain this diversity, the truth is that scientists have not succeeded. Now, the journal ‘Science Advances’ has just published a study, the first of its kind, in which an extensive team of researchers, including the Spanish paleontologist Juan Luis Arsuagaco-director of the Atapuerca sites and scientific director of the Museum of Human Evolution (MEH), analyzes for the first time with 3D CT the frontal sinuses of individuals from all species of human evolution.
“Something like this had never been done before,” explains Arsuaga to ABC, “it is a tremendous job, carried out by many people for many years. We started with CT scans in the 90s, at the 12 de Octubre hospital. We were among the first, we were pioneers and working in Spanish centers». For this research, Arsuaga has thus analyzed the fossils of six individuals from Atapuerca and others from the site of masticin Portugal.
A starting point
Unlike conventional radiographs, Computerized Axial Tomography (CAT) allows the skull and its components to be studied in three dimensions, as if it were transparent. The technique consists of scanning the fossil layer by layer, in very thin sheets that are then ‘assembled’ in the computer until a complete virtual piece is obtained. “A huge job -says Arsuaga-, but that is only a starting point”.
The titanic effort carried out by the researchers, in fact, will serve from now on to carry out hundreds of new studies that were not possible before. «The enormous amount of information published in the article -continues the paleontologist- is a real mine for future research, because never before has such a complete catalog of fossils been made available to the scientific community. The big question is this: what does the size of the frontal sinuses in a skull depend on? And why is there so much diversity? Questions that, according to Arsuaga, could be answered in the future.
«There have been two great revolutions in paleontology -explains Arsuaga-. That of DNA and that of TAC, which is a new way of looking at fossils. Now we have all this information, just like when the DNA of a Neanderthal was sequenced. From now on we will see what all this information can tell us. I hope that in the future it will be possible to see the reason for the variation that we observe, why there are human species that have different frontal sinuses. We will be able to see if the reason is or not in the climate, in the brain, we will be able to know why Neanderthals were so different from modern humans…».
A new species?
Although it is not the objective of this scientific work, Arsuaga aims high and suggests the possibility that the study also contains clues that lead us to a new human specieshitherto unknown.
“It is my conclusion,” Arsuaga tells ABC, “but having such a complete catalog in hand, I decided to look at the case of the three skulls in the fossil record that have the largest frontal sinuses: they are those from Broken Hill, in Zambia. , that of Bodo, in Ethiopia, and that of Petralona, in Greece. Those three skulls catch my attention because they have some monstrous frontal sinuses, so large that their frontal lobes have had to shrink. Because they share this trait, all three have been grouped under the name of A man from Rhodesia«.
But Arsuaga goes further: «What can this extraordinary similarity mean? His frontal sinuses stick out, jump out at you. It has been said that, in all three cases, we are dealing with extreme individuals, exceptions, but I don’t think that is the case. In Atapuerca we have many individuals from the same period, and none of them have such enormous frontal sinuses. However, something tells me that if these three skulls are so similar, they must be related in some way. All three lived in tropical or Mediterranean climates, so the explanation that the size of the breasts was to protect the frontal lobe from the cold is ruled out,” says the researcher.
The mystery does not end there: «They also have the chronology in common, between 500,000 and 250,000 years. In the world there is Homo erectus, Java, ancestors of the Neanderthals… and then here is this ‘something else’. Something else we don’t know about must be out there. Something that is not being talked about. But it’s my impression, my first impression. These three skulls are neither like the ones from La Sima nor like the Asian ones. There was something there … and I think it would not be unreasonable to think that the same represent a totally new human species or subspecies ».