Craniofacial Secular Change in Recent Mexican Migrants

Abstract

Research by economists suggests that recent Mexican migrants are better educated and have higher socio-economic status (SES) than previous migrants. Because factors associated with higher SES and improved education can lead to positive secular changes in overall body form, secular changes in the craniofacial complex were analyzed within a recent migrant group from Mexico. The Mexican group represents individuals in the act of migration, not yet influenced by the American environment and as such can serve as a starting point for future studies of secular change in this population group. The excavation of a historic Hispanic cemetery in Tucson, Arizona also allows for a comparison of historic Hispanics to recent migrants for the purpose of exploring craniofacial trends over a broad time period as both groups originate from Mexico.The present research addresses two main questions: 1) Are cranial secular changes evident in recent Mexican migrants? and 2) Are historic Hispanics and recent Mexican migrants similar? By studying secular changes within a migrant population group, secular trends may be detected, which will be important for understanding the human biology of the migrants themselves as well as serve as a preliminary investigation of secular change within Mexican migrants. The comparison of recent Mexican migrants to a historic Hispanic sample, predominantly of Mexican origin allows for the exploration of morphological similarities and differences between early and recent Mexicans within the US.A total of 82 craniofacial inter-landmark distances (ILDs) and vault and face size were used to explore secular changes within the recent Mexican migrants (females = 38, males = 178) and to explore the morphological similarities between historic Hispanics (females = 54, males = 58) and recent migrants. Sexes were separated and multivariate adaptive regression splines and basis splines Pre-print version. Visit http://digitalcommons.wayne.edu/humbiol/ after publication to acquire the final version.(quadratic with one knot) were used to assess the direction and magnitude of secular trends for the recent Mexican migrants. Because dates of birth were unavailable for the historic sample, partial least squares discriminant analysis (PLS-DA) was used to evaluate morphological differences between historic and recent Mexican Migrants. The data was separated into a training and a testing dataset to ensure realistic results.Males presented with eight variables (four positive and four negative) and females presented with six variables (two positive and four negative) that demonstrated significant differences over time. In the PLS-DA, three components were identified as important in model creation and resulted in a classification accuracy of 87% when applied to a held out sample. The high classification accuracy demonstrates significant morphological differences between the two groups with the historic Hispanic sample displaying overall larger craniofacial dimensions.While differences in cranial morphology are evident bet...

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