The structure of cranial morphological variance in Asia: Implications for the study of modern human dispersion across the planet

Abstract

The study of past human dispersion is a central topic to understand how humans occupied the planet. However, this is not a simple task, as it depends on our ability to estimate the ancestral state of past populations based on the biological diversity observed among samples, before this can be used to infer phylogenetic relationships between them. Studies dedicated to this type of analysis rely on understanding the forces that structured the variance between and within the groups studied. For complex phenotypic data, like cranial morphological variation, this task is especially challenging due to the combination of factors that contributed to the observed pattern of variance among modern human groups. In this chapter, I explore the structure of the morphological variance within and between Asian regions, to illustrate the importance of considering the myriad of evolutionary forces structuring the morphological variance among regions when reconstructing past human dispersion. Using a large craniometric dataset representing three Asian macro-regions, I compare, through the estimation of QST values, the apportionment of variance in Asia and compare it to the values obtained for other regions of the planet. The results are contextualized within four continent-wide periods of human dispersion. Taken together, they suggest that Asia’s morphological diversity is mostly defined by a geographic structure, same as the rest of the planet, but there are significant departures from this pattern when analyzing Northeast Asia. This analysis shows that local conditions can impact significantly the structure of morphological variance and must be considered in the reconstruction of past dispersion events.