Variation in human hair morphology within and among human populations

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Human scalp hair varies considerably in form and color, within and among human populations. This study will analyze recently collected hair samples representing a wide range of human populations, enabling an unprecedented microscopic investigation of variability in human scalp hair features and laying the groundwork for future research that links hair form and color with their underlying genetics. The project will advance science and benefit society by providing additional measures of hair variation that can be used in forensic contexts to address questions of ancestry and personal identification, and by providing new information on how the forces of evolution have influenced hair morphology in our species. The investigators will apply recent technological advances in optical microscopy, transmission electron microscopy (TEM), and three dimensional scanning electron microscopy (3D SEM) to define and measure the dimensions of external hair forms and internal structures. Specific attention will be focused on identification of patterns of variation in curl patterns, cross sectional dimensions, cuticle thickness, and orientation of cortical structures within and along the length of the hair shaft. The nature and significance of the observed patterns of variation will be rigorously tested using appropriate statistical methods. Because the hair samples are associated with genotyped DNA samples, future studies correlating single nucleotide polymorphisms (SNPs) and morphological variation will be possible. These investigations are expected to shed light on the range of diversity in human hair forms, illuminate instances of convergent evolution in hair form, and suggest specific avenues for further exploration of the relative roles of natural selection, gene flow, and genetic drift in the evolution of human scalp hair form. By understanding the morphological hair features in detail the investigators will be able to plan efficient and focused phenotyping programs for both gene discovery and forensic efforts.This project is jointly supported by the National Institute of Justice and the Biological Anthropology Program at NSF.