Admixture and population dynamics in the Philippines through craniometric analysis

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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.