Admixture and population dynamics in the Philippines through craniometric analysis

Abstract

The Philippine population prior to European contact is the result of the arrival to the archipelago of different subgroups and the admixture between them. Taking the skull as a complex genotype resulting from both genetic inheritance and the environment, and assuming populations with phenotypic similarity will have a greater phylogenetic relationship, the possibility of studying admixture based on geometric morphometry and cranial measurements is proposed. Sixty-one skulls from a collection from the National Museum of Anthropology in Madrid (MNA, Spain) were studied, all dating from before the 19th century. As a reference, the Howells (1973) database was used. The characterization of the phenotype was carried out using a Microscribe digitizer arm with which 65 landmarks were taken, using them to create 12 craniometric distances. The admixture of the Philippine skull collection from the MNA was evaluated by applying a Discriminant Analysis based on Gaussian finite mixture modeling. Thanks to a principal component analysis, a study of morphospaces was carried out. Additionally, a population inference was made using the Relethford and Blangero model. Finally, the skulls were divided into clusters according to their admixture using the k-means method. The individual admixture of each skull was estimated, and later the collection was divided into three clusters after applying the k-means method. The Relethford and Blangero analysis indicated that the groups created did not have much internal admixture, unlike the Filipino group in the Howells database. Assuming a relative neutrality of the craniofacial characters, it is possible to study the admixture of some individuals from a series of cranial distances. This study is framed in the line of other genetic, linguistic, or morphometric types, which indicate that the Philippine population prior to the 19th century has a great intrapopulation variance, constituting a series of metapopulations within the entire archipelago.