Just a quick one today. I read an article earlier this week over on Live Science about the evolution of Neanderthal skull form and thought that one point in the article needed a bit of clarification.
“[…] many of the Neanderthal-like features in the Sima fossils were related to chewing. “It seems these modifications had to do with an intensive use of the frontal teeth[…] The incisors show a great wear, as if they had been used as a ‘third hand,’ typical of Neanderthals.”
Sima refers to Sima de los Huesos, or Pit of Bones, a very important fossil site in Spain where all of the Neanderthal fossils used to draw this conclusion were found.
The authors mention that one of the first behaviours to characterise Neanderthals was the use of their teeth as a tool, or a ‘third hand’ as it was put in the original article. While this is a well-accepted behaviour of Neanderthals, there has been quite a bit of debate as to how important this behaviour was in Neanderthal evolution (e.g. Rak, 1986; Spencer & Demes, 1993; Clement et al., 2012).
Figure 1.The anterior Dental Loading Hypothesis. String incisor bites causes rotation of the face (top). In response, Neanderthals evolve to resist this bending (bottom). Credit: Rak, 1986.
In the early days, it was thought that habitual strong biting at the incisors would cause rotation of the face as shown by the arrows in fig. 1 (left, top). It’s well-known that the skeleton responds to stresses and strains by laying down more bone in the most highly stressed regions. It was thought that this process could result in the more protruding faces of Neanderthals, whose triangular plate of bone below the eyes and around the nose provided strength to resist bending and rotation (Rak, 1986). This is known as the Anterior Dental Loading Hypothesis.
Very soon after, people started disagreeing with this view (e.g. Trinkaus, 1987) but the debate continues (e.g. Clement et al., 2012), with studies focusing on modern Inuit who also exhibit highly worn incisors as a result of using them for behaviours other than feeding, namely to process seal hides to prepare them for clothing.
Although Neanderthals and modern Inuit populations both exhibit comparable alterations in facial form to be able to produce stronger bites at the incisors, the degree of wearing is no different between the two. Therefore, if the effects of habitual strong biting at the incisors were responsible for Neanderthal facial form, we would expect to see similar facial shape in modern Inuit populations, which is not the case.
Based on this, the Anterior Dental Loading Hypothesis is unlikely to be true.
To re-iterate, I agree with the quotation that Neanderthals used their teeth as tools, and it also seems that this behaviour was important early on in the evolution of Neanderthals.
However, the Live Science article isn’t very careful about separating the appearance of dental wear in the fossil record from the evolution of the protruding Neanderthal facial shape.
I hope I’ve been slightly clearer.
p.s. A huge fossil-themed thank you to everyone who’s helped me reach 2000 views!
Clement, A. F., Hillson, S. W., & Aiello, L. C. (2012). Tooth wear, Neanderthal facial morphology and the anterior dental loading hypothesis. Journal of Human Evolution, 62, 367–76. doi:10.1016/j.jhevol.2011.11.014
Rak, Y. (1986). The Neanderthal: a new look at an old face. Journal of Human Evolution, 15, 151–164.
Spencer, M. A., & Demes, B. (1993). Biomechanical analysis of masticatory system configuration in Neandertals and Inuits. American Journal of Physical Anthropology, 91, 1–20. doi:10.1002/ajpa.1330910102
Trinkaus, E. (1987). The Neandertal face: evolutionary and functional perspectives on a recent hominid face. Journal of Human Evolution, 16, 429–433.