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Blog científico

Publicado el 28 de November de 2013 por María Martinón

The face of Homo sapiens, a 'vintage' design

In a society like ours, so concerned about aesthetics and fashion, we should know that our face is a vintage design. No more and no less than a million years ago, evolution made a graceful, vertical face with almost sunken cheeks–technically called orthognathous–that had nothing to do with the simian and prognathous face of hominids that had existed until then. Nearly a million years ago, our face, that great first business card in encounters among humans, was already `modern`. As modern as the modern man who inhabits our planet in the 21st century. When, in the year 1997, a new human species from the remains found at the TD6 level of the Gran Dolina was published in the Science magazine, the scientific community received this new family member with reluctance. For Atapuerca's Team researchers, the identified hominids at the site had a combination of previously unknown features: a very primitive dentition with a modern mid-facial morphology. This interpretation raised suspicions and, in essence, it's no wonder. The paradox that something so modern was yet so old was surprising. 

 

One of the main criticisms was that the derived character was primarily defined by an immature fossil, now known as the Gran Dolina Boy and sceptical researchers argued that the graceful and vertical look in the boy's face would disappear in an adult Homo antecessor when his face growth would become complete. This criticism, however, was not based on available data. In fact, a fragment of an adult's face had also been found at TD6 and although this gracefulness was not as pronounced as in the young individual, it still retained a modern look. For unbelievers, the Gran Dolina fossils did not represent a new species, but belonged at most to the Homo ergaster, a species of African origin up to 1,8 million years old. Fortunately, the fact of having an immature individual available would be an additional advantage when, fifteen years later, the Atapuerca team, in collaboration with a team of Hispanic-American researchers, would address this question about the face again. This time it was about studying the bone growth pattern, comparing the face of the Gran Dolina Boy with the face of the Turkana Boy, another fossil boy about the same age. Interestingly, he had been identified as Homo ergaster, the species to which some had attributed the TD6 fossils. Bone is a tissue that works by forming itself (technically called bone deposition) and destroying itself (bone reabsorption) depending on the area and the circumstances. In the case of the Homo antecessor face, bone was mainly reabsorbed, just as it is reabsorbed in modern humans, producing such a thin face. However, in the same facial areas of Homo ergaster, bone was being deposited, producing a large face as a result. The face was also protruding, as if it were `inflated`. 

 

This experiment meant it was almost possible to make a `live` comparison between two individuals who were dead, freezing them at a crucial and decisive moment of their biology, when they were growing. Moreover, it was necessary to add to this important facial feature the fact that Homo antecessor had a considerable cerebral size, more than 1000 cc and therefore bigger than that of former human species. We also know that their pattern of dental development, a process closely interwoven with how a species grows, was also like that of modern humans. Through a generally slower and more prolonged growth, proportionally larger brain growth than for any other mammal was possible. The Gran Dolina fossils heralded for the first time–to our knowledge–the occurrence of childhood in humanity. It is interesting to discover that through the fossil history of the Iberian Peninsula, itself, almost an `island` of the great Eurasian continent, we are able to study a crucial and universal moment of human evolution. Fossils of the Gran Dolina of Atapuerca are the best preserved witness that exists today of that qualitative change which distinguishes us from earlier human species and set us on the path to what we are now. Some may find it surprising that we can tell stories that are so universal rather than `local` from one end of the great continent. But that's how it is.

 

TD6 hominids are today the most complete window through which we can hope to understand what happened in humanity one million years ago, when substantial changes in the fossil record are recorded, not only in the face but in other biological aspects related with growth, which is what defines whether we are one species or another at the end of the day. If Homo antecessor came back to life, it would probably be surprised at many things: at a paved planet, at `caves` with roofs and windows, at boned meat (but not human) ready to eat. And that sometimes metal birds sail the sky, without beating their wings. Such “raw material” would, of course, be unknown to it. However, it wouldn't be surprised at our faces, at our `retro` face, because it would find it familiar. Wouldn't it? We know it's the same face but, were emotions the same? Did their gestures codify the same feelings? Did their faces have the same way of expressing them? The same way of hiding or faking them? Is it a face or a mask? Whose soul, whose animal, is that face a mirror? Every time we see ourselves reflected, we're greeted by the antecessor we have within.