Doctoral Dissertation Improvement: Environmental Effects on Human Cranial and Postcranial Sexual Dimorphism

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Knowledge of the environmental plasticity of both body size and craniofacial traits in humans will impact long-term human evolutionary studies, and may be used to test behavioral psychology theories of human sexual selection. A better understanding of the sex-specific environmental plasticity of human dimorphic features would provide information regarding biological and cultural adaptations, bioarchaeological collections, and a tool to infer environmental stresses endured by archaeological populations. Documenting population variations in body size and craniofacial dimorphism is key to developing population-specific sex determination methods in forensic and bioarchaeological contexts. In addition, the use of 3D surface scanning technology provides new quantification and storage opportunities that allow for future analyses as software advances, facilitates data sharing, and supports collaboration in situations where researchers cannot physically travel to collections. The project will also support the training and professional preparation of a female graduate student. The factors influencing cross-cultural variation in modern human cranial and postcranial sexual dimorphism are not well understood. Some evidence suggests that females may be better buffered against environmental stressors, resulting in a systematic decrease in body size dimorphism in samples under poor conditions. In contrast, dimorphism in craniofacial traits such as brow ridge and chin morphologies has been hypothesized to be related to mate preference and sexual selection, and should be environmentally neutral or even increase under poor climatic conditions. Quantifying such discrete craniofacial traits, however, has proven challenging, and the subjectivity of traditional qualitative methods prevents objective statistical analyses between the sexes or across populations. This project utilizes a novel method of quantifying cranial trait morphologies to examine the relationship between craniofacial trait dimorphism and postcranial size dimorphism with various environmental stressors. A geometric morphometric method will be used to objectively quantify sexual dimorphism in brow ridge and chin morphologies using 3D laser surface scans. Sexual dimorphism in these craniofacial traits and skeletal measures of body size will be evaluated in an array of ethnically and culturally diverse populations. Specific comparisons between genetically related, yet environmentally disparate samples will be employed in an attempt to isolate the effects of individual environmental factors on postcranial and cranial sexual dimorphism.