This dissertation explores nonmetric sexual dimorphism and cranial nonmetric variability in 1,397 modern Japanese and Thai individuals between the ages of 17 and 96 years.
The author of this dissertation seeks to address a gap in research by testing assumptions, based on a distantly shared genetic history, that Native Americans and Asians are homogenous and share nonmetric sexually dimorphic skeletal features and a unique suite of cranial traits that can be used in ancestry assessment. The research study explored nonmetric sexual dimorphism and cranial nonmetric variability in 1,397 modern Japanese and Thai individuals from 17 to 96 years of age. The study had two stated objectives: to test and refine the methods based on 15 traits used to predict sex from the cranium, pelvis, clavicle, and humerus that were developed on non-Asian populations; and to establish 36 cranial and mandibular trait frequencies to determine if the Japanese and Thai differ from each other and Native Americans in trait expressions. Results indicated several things: that population-specific sex assessment methods performed better in classifying the Japanese and Thai compared to those developed in non-Asian populations, and produced correct classification rates of 66 to 98 percent; the majority of cranial and mandibular traits used in ancestry assessment significantly differed in frequency between the Japanese and Thai, resulting in correct classification rates of 60 to 90 percent; and that Japanese and Thai are different from Native Americans in the expression of nonmetric traits. The author notes, however, that sex, age, population, intraobserver error, and secular change affected many nonmetric traits and complicated their use in sex and ancestry assessment. The author reports that Japanese, Thai, and Native Americans are not skeletally homogenous, and that this research highlights the importance of developing population-specific biological profile methods for diverse Asian populations.