The Human Mandible and the Origins of Speech

Table 1

Torsional strength of hominoid mandibles.

Taxon	Mean	Standard error	Range	T/K ratio
Homo	542	37	292–1072	1.6
Pan	556	40	314–896	2.4
Pongo	879	68	490–1456	1.1
Gorilla	1729	102	1198–2808	0.9

𝑁=20 (10 males, 10 females) for each taxon. Means, standard errors and ranges are for a thin-tube model for torsional strength (K, units in mm³), which determines strength as a function of area and minimum wall thickness [17, 44]. Nonparametric ANOVA for mean values of K is significant at 𝑃<0.001. Post hoc tests reveal that all pairwise comparisons are significant with the exception of Homo versus Pan (𝑃>0.05). The T/K ratio estimates torsional shear stress, where 𝑇 is the applied twisting moment. Since the twisting moment arm is difficult to estimate from skeletal material, the moment arm is assumed constant (1.0, arbitrary units), and the applied force is considered to be the summed estimated forces of the jaw adductors from reference [34].