Population biodistance in global perspective: Assessing the influence of population history and environmental effects on patterns of craniomandibular variation

Biodistance studies have a long history of usage in bioarchaeology and bioanthropology in order to better understand the causes of particular among-group patterns of biological affinity. Here, using two specific case studies, a biodistance analytical framework is implemented to assess the microevolutionary history of global patterns of human craniomandibular variation. In these case studies, the biodistance patterns concern global among-population cranial and mandibular shape distances, quantified using an explicit evolutionary quantitative genetic model. In the first case study, a null model of neutral evolution is tested for global cranial shape biodistance using two analytical approaches: Mantel tests, and Procrustes rotation of 3D multidimensional scaled ordinations of original distance matrices. The results confirm that overall global patterns of cranial shape variation broadly conform to neutral expectations. However, population-specific residual analyses show that some populations conform less well to the neutral model and may be affected by climatic adaptation. The results from the second case study, using the same analytical techniques, show that, contrary to cranial shape biodistance, mandibular biodistance does not conform to neutral expectation, correlating instead with major differences in subsistence behavior among groups. These case studies further illustrate the flexibility of a biodistance matrix framework for integrating multiple potential sources of information regarding neutral population history and nonneutral adaptation, at a broad global level.