A note on functional implications of morphological variation in the human mandible

This study was carried out on 56 mandibles belonging to skeletal remains recovered from archaeological excavations in Israel dated to 6.000 BP. or less, 2 Neandertal mandibles dating between 50.000-60.000 BP. and 2 early H. sapiens sapiens mandibles both dating to circa 92.000 yr BP. Mandibular body length, the distance from the anterior border of the symphysis to a line bisecting the first molar (distance 1), and the distance from the line bisecting the first molar to the mandibular angle (distance 2) were measured. Distance 1, showed little variation between specimens. However, distance 2 showed a significant difference between sexes and between early and late specimens. For all specimens examined there was a low nonsignificant correlation, between the length of the mandible and distance 1, while there was a high correlation between the length of the mandibular body and distance 2. There was little or no correlation between distance 1 and 2. We propose that the human mandible, as a lever arm, can be divided into two functional parts; an anterior part which shows little change over the last 90000 years, and a posterior part which differs in accordance with the length of the mandibular corpus. These changes in distance 2 appear to correlate to changes in body size and diet, suggesting that as proposed by Hylander (1988) chewing rather than incision has played the main role in evolutionary trends of the hominid mandible. This is also in accordance with mandibular growth during development where the lengthening of the jaw takes place mostly in the posterior part by remodeling in the ramus area (Enlow, 1990) both during individual development (ontogenesis) and through evolutionary changes (phylogenesis).