Wednesday, 9 July 2014

Faces of Evolution - validating the methodology for facial reconstruction of hominids

Face of a Homo erectus pekinensis reconstructed from the deformation of the reconstructed CT scan of a modern man
In facial reconstruction, most secure information are those obtained based on the soft tissue thickness tables. They are elaborated from the measurement of the distance between the outer surface of the skin, going through muscles, fat and other soft tissue s to the bone, at specific points, spread over the head and may vary within an average  quantity of 21-33 landmarks, depending on the protocol used . These thicknesses can be obtained from people who have died recently or even in living individuals using ultrasounds or CT scans

And what use do these measures have in facial reconstruction? It's very simple, they work as a reference for the artist or scientist, which uses these points to make a "reverse engineering", because from the bones of the skull one can estimate how much soft tissue there was at these specific points, and approximate the volumetric shape of that individual based on a statistical method.

Stages of the adaptation of skull and skin of a modern man over the skull of a H. erectus pekinensis.
The problem arises when dealing with cases without soft tissue tables, such as our hominid ancestors. How to do this research for such beings, which are already extinct for thousands and/or hundreds of thousands of years?

To overcome this problem I thought of a conceptually simple solution but that charges a certain skill to be applied. In the case of hominids that look more like the modern man, such as neanderthalensis, pekinensis and rhodesiensis we can use the scans of modern humans, filter the skin and the skull and then deform them until the man's skull suits the hominid skull. Of course the skin is put in another layer so its view does not interfere in the work and at the same time. It also allows the focus to be restricted to the skull, that is the only sound piece that is left of that animal.

Paranthropus boisei, a hominid reconstructed from the deformation of the skull and skin of a Pan troglodytes (chimpanzee).
For other hominids such as Paranthopus boisei, Homo habilis, Australopithecus afarensis and the like, we apply the same procedure but using a reconstructed CT scan from a Pan troglodytes as the object for deformation.

So far so good, it was clear that this was an ingenious way out ... but would it be valid? Would that deformation be compatible with the volumetrics of the hominid in question?

To answer these questions I leaned on Archaeologist Luca Bezzi's rationale, put forward during a meeting in which we participated in Italy, in occasion of the preparations for FACCE, il molti volti della storia umana. Bezzi proposed a simple and interesting experience... he said, if the method was valid, theoretically it could convert a chimpanzee into a gorilla (Gorilla gorilla) and vice and versa. I found that assumption fantastic and decided to perform it as soon as I returned to Brazil.

To get a gorilla, I resorted to a database of CT scans from KUPRI, Primate Research Institute Kyoto University, in Japan (PRICT. 296). Despite being with an "open mouth" the model I found seemed good, because the head was complete and it was an adult, as well as the chimpanzee used as a source object of deformation.

Although they look like the same creature at first glance, there are many structural differences between a chimpanzee and a gorilla. By adapting the skull of the first one, using the second as a reference, I was quite anxious to see the final result. Even a seemingly intelligent and well thought out solution, as I carried out a test with such rigor and the need to reach a pre-determined outcome, I confess that I feared falling into the arms of failure.

As I finished the settings and turned on the layer containing the already deformed chimpanzee's skin, I realized that the method had achieved a high degree of compatibility. I still must test the deformation of a gorilla... but I will leave it to another occasion, when free time allows me to do it. For now I will take some time and just enjoy the delight that this experience has given me.

OBS.: I have to thank Dr. Paulo Miamoto that made this translation from the original post in Portuguese. Dr. Miamoto is a Ph.D in Dentistry and coordinator of the EBRAFOL - Brazilian Team of Forensic Anthropology and Legal Dentistry.

A big hug!
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