1Department of Anthropology, Pennsylvania State University, 2Department of Biology, Pennsylvania State University, 3Department of Anthropology, University of Utah, 4School of Life Sciences, Arizona State University
March 28, 2019 4:45, CC Room 26 C
Human scalp hair morphology is highly variable. However, unlike skin pigmentation, there is no widely used method of quantifying scalp hair variation. Therefore, hair continues to be described by geneticists as ‘straight’, ‘wavy’, ‘curly’ and ‘frizzy’. Such oversimplifications of this complex trait, combined with a focus on Eurasian populations, have likely contributed to our lack of knowledge of its genetic basis and evolution in humans. To fill these gaps in our understanding, we developed software to accurately quantify hair fiber morphology and used it to measure hair in a sample of 195 individuals with mixed African and European ancestry. We used these measurements, combined with genomic data, to investigate the effects of ancestry and selection on hair morphology. We found that hair curvature is highly correlated with the percentage of African ancestry (r = 0.84, 99% CI [0.80, 0.89]), which is as strong as the correlation between skin pigmentation and African ancestry in the same sample (r = 0.82, 99% CI [0.76, 0.87]). To understand the role of selection in shaping hair morphology, we performed tests for selection on genes known to be important in hair biology. One of these, LPAR6, exhibits convergent signals of positive selection in both African and Melanesian populations, suggesting that populations with tightly curled scalp hair may have faced similar selective pressures. Our high-throughput and objective phenotyping method has the potential to uncover fine-scale variation therewith improving large-scale gene mapping, as well as, evolutionary and heritability studies of hair morphology.
This work was supported by the Center for Human Evolution and Diversity and the Department of Anthropology at the Pennsylvania State University.