A geometric morphometric approach to cranial variation of southeast Asians in a global context

This study examines cranial shape variation of modern and near-modern southeast Asians in a global context, expanding on earlier studies by utilising geometric morphometric techniques to gain new perspectives. The three-dimensional co-ordinates of 54 landmarks from six southeast Asian and five comparative populations (143 individuals) were analysed using the shape analysis software, Morphologika. Variation of cranial shape was examined by calculating Procrustes distances between samples; a cluster analysis was then used to summarise phenetic relationships. Principal components analysis and thin plate splines allowed for the statistical and visual exploration of shape differences. Results of the Procrustes distances, cluster analysis and PCA show a distinct separation between the southeast Asian samples and comparative samples from northeast Asia, Australia, Africa and the United Kingdom. Observed shape differences include rendered images and thin plate splines depicting a relative globular shaped vault, flat upper face and narrow facial breadth as characteristic of southeast Asians. These features do not appear to have a significant association with size or latitude, suggesting the presence of an underlying genetic signal. The shape of the midface, frontal bone and alveolar region were, however, among cranial features that did exhibit a significant correlation with latitude. Results of this study are tentative given the limited nature of the dataset (eg, small sample sizes). Despite this, the findings support recent consensus views that cranial morphology is indicative of both genetic relationships and environmental influences, which has important implications for the use of cranial morphology to infer population histories.