Cranial variation of contemporary East Asians in a global context

The current study examines cranial variation of contemporary East Asians with an aim to comprehensively describe and define the morphology of people in this region. In doing so, a better understanding of the causes of variation within East Asia and compared to other geographic populations is sought. The study encompasses a broad range of samples from Northeast Asia to island Southeast Asia. Traditional linear and angular data and analytical methods (e.g Box and Whisker, Principal Components Analysis) were used to assess cranial variation. Thus the results may be compared to published studies using traditional craniometric approaches. Innovative geometric morphometric data collection and analysis techniques are also used here for the first time. Results show East Asians are distinguishable from non-Asians on the basis of their tall, round, vault, shorter cranial length, tall faces that are flattened in the upper and mid-facial regions, short malars (anteroposterior length), narrow interorbital breadth and orthognathism. A north-south East Asian cline was also detected, with the northern samples exhibiting tall, orthognathic faces, and a long low vault. This long, low vault shape is in contradiction to the purported shape of cold-climate adapted populations. Southern East Asians possess a tall, rounded vault and a short, projecting (prognathic) face. Island Southeast Asians inhabiting the Andaman and Nicobar Islands exhibit a 'mixed' morphology, possessing the southern East Asian facial form, but the long, low vault seen in northern East Asian samples. The long, low vault also characterises non-Asian samples from Australia, Africa and Melanesia. Shape differences were significantly associated with latitude, explaining most of the variation. The identification of ancestral East Asian features in recent samples suggests phylogenetics may also be contributing to variation in part. The study concludes that there is clear evidence for geographical variation among modern East Asians, some if it being continuous (clinal) and some discontinuous. Importantly, much of the variation reflects adaptation to climate, with a phylogenetic component also recognised. The study contributes to our understanding of human evolution in a region that today constitutes around half of the world?s population