June 23, 2010

Modern humans bite hard

From the paper:
Our findings offer an explanation for the apparently inconsistent presence of a dentition in H. sapiens that appears well adapted to resist high bite forces relative to other extant hominids, set in a cranium and mandible that are relatively gracile and characterized by less robust musculature. Thus, the teeth of humans need to be able to resist comparable bite reaction forces to those of other extant hominids, but, because considerably less muscle force is required to achieve any given bite reaction force in the human than in other hominids, less stress is produced.


We conclude that although humans are well adapted to produce high peak forces with the jaw moving in rotation, they may not be as well adapted to produce and maintain high bite forces with the jaw moving in translation. Thus, Homo sapiens may be comparable to other hominids in possessing an ability to access some relatively hard foods through the application of high transitory bite forces, however, our species may be less well adapted to consume tough or hard foods that require powerful, sustained chewing.
Proceedings of the Royal Society B doi: 10.1098/rspb.2010.0509

The craniomandibular mechanics of being human

Stephen Wroe et al.

Diminished bite force has been considered a defining feature of modern Homo sapiens, an interpretation inferred from the application of two-dimensional lever mechanics and the relative gracility of the human masticatory musculature and skull. This conclusion has various implications with regard to the evolution of human feeding behaviour. However, human dental anatomy suggests a capacity to withstand high loads and two-dimensional lever models greatly simplify muscle architecture, yielding less accurate results than three-dimensional modelling using multiple lines of action. Here, to our knowledge, in the most comprehensive three-dimensional finite element analysis performed to date for any taxon, we ask whether the traditional view that the bite of H. sapiens is weak and the skull too gracile to sustain high bite forces is supported. We further introduce a new method for reconstructing incomplete fossil material. Our findings show that the human masticatory apparatus is highly efficient, capable of producing a relatively powerful bite using low muscle forces. Thus, relative to other members of the superfamily Hominoidea, humans can achieve relatively high bite forces, while overall stresses are reduced. Our findings resolve apparently discordant lines of evidence, i.e. the presence of teeth well adapted to sustain high loads within a lightweight cranium and mandible.



aargiedude said...

Here are some things I'm curious about. Seems like there's one notable difference between humans and everybody else, and that's in the chin region, where we apparently have a lot more stress than any other ape. And we're also supposed to be the only ape or hominid that has a developed chin, right? I never really understood that chin thing. It might sound dumb, but I don't see it. What exactly does it mean that we have a chin and they don't? I'm looking at the images and I don't understand that. They all have a chin to me.

I'm wondering if the changes in our jaw anatomy might be an indirect result of speech. In other words, the evolution of the differences observed by the scientists would be more an adaptive reaction to the changes needed for speech, like a compromise to best accomodate both needs, than the result of evolving a new, more efficient mastication process.

eurologist said...

So, looking at the stress image, did we develop a chin because of the relatively gracile lower jaw that distributes forces more evenly?