Morphological variation in great ape and modern human mandibles

Abstract

Adult mandibles of 317 modern humans and 91 great apes were selected that showed no pathology. Adult mandibles of Pan troglodytes troglodytes, Pongo pygmaeus pygmaeus and Gorilla gorilla gorilla and from 2 modern human populations (Zulu and Europeans from Spitalfields) were reliably sexed. Thirteen measurements were defined and included mandibular height, length and breadth in representative positions. Univariate statistical techniques and multivariate (principal component analysis and discriminant analysis) statistical techniques were used to investigate interspecific variability and sexual dimorphism in human and great ape mandibles, and intraspecific variability among the modern human mandibles. Analysis of interspecific differences revealed some pairs of variables with a tight linear relationship and others where Homo and the great apes pulled apart from one another due to shape differences. Homo and Pan are least sexually dimorphic in the mandible, Pan less so than Homo sapiens, but both the magnitude of sexual dimorphism and the distribution of sexually dimorphic measurements varied both among and between modern humans and great apes. Intraspecific variation among the 10 populations of modern humans was less than that generally reported in studies of crania (74.3 % of mandibles were correctly classified into 1 of 10 populations using discriminant functions based on 13 variables as compared with 93 % of crania from 17 populations based on 70 variables in one extensive study of crania). A subrecent European population (Poundbury) emerged as more different from a recent European population (Spitalfields) than other more diverse modern populations were from each other, suggesting considerable morphological plasticity in the mandible through time. This study forms a sound basis on which to explore mandibular variation in Neanderthals, early Homo sapiens and other more ancient fossil hominids.Key words : Hominoids ; mandible ; sexual dimorphism. In recent years, a number of important fossil mandibles attributed to both Neanderthals and early Homo sapiens have been recovered. At the same time debate about human evolution has come to focus more sharply on the origins of modern Homo sapiens. Potentially, fossil mandibles such as those, for example, from Heidelberg in Germany, Klasies River Mouth in South Africa, and those from Tabun, Kebara, and Qafzeh in Israel, which differ considerably in their size and morphology, may help shed light on this key issue. However Neither is it clear how certain fundamental mandibular dimensions such as height, breadth and length, relate to mandibular size and to each other and to what extent apparently contrasting mandibular morphologies may simply be a consequence of body size and sexual dimorphism. Despite the fact the mandible is better represented in the the hominid and hominoid fossil record than most other bones there are still many more comparative studies of the cranium than there are of the mandible.To explore these issues we have undertaken a

Talking heads: Morphological variation in the human mandible over the last 500 years in the Netherlands

“…While some scholars argue that the mandible is of not much value in identifying recent human populations (e.g. Humphrey et al, 1999), other recent studies have pointed out that actually, the mandible can reflect population history quite well, as inferred from geographical distance between populations (Nicholson and Harvati, 2006;Harvati and Weaver, 2006), but also from "population continuity" (Galland et al, 2016;Šešelj et al, 2015). Geographical distance might be a fairly robust proxy for inferring restricted gene flow between populations and a good estimate of different climatic conditions.…”

Global human mandibular variation reflects differences in agricultural and hunter-gatherer subsistence strategies

“…One of the most obvious alternative models is that agricultural populations will experience different biomechanical or selective pressures on mandibular shape than hunter-gatherers, such that modifications have occurred either via phenotypic plasticity or natural selection. Previous morphometric studies (23,24) found some geographical patterning in mandibular morphology, as well as a signal of climatic and/or masticatory plasticity. However, hunter-gatherer and agricultural populations have never explicitly been compared at a global level to evaluate the likely role of subsistence economy in the evolution of the mandible.…”

Superior position of the mandibular foramen and the necessary alterations in the local anaesthetic technique: a case report

“…Geographically two of the most variable measurements are the height (superoinferiorly) and the width (anteriorposteriorly) of the ascending ramus. 3 Dental nerve blocks are based on anatomic norms and statistical averages of nerve pathways and bone structure. Any variation from the 'average patient' can result in failed anaesthesia, as suggested in our case study.…”