Variation and Heritability in Hair Diameter and Curvature in an Australian Twin Sample

The study measured hair diameter and curvature in 2,332 Australian twins and siblings using an optical fiber diameter analyzer and found that these traits were highly heritable. Genetic factors accounted for 86% of the variance in hair diameter and 53% in curvature for males, and 77% in diameter and 61% in curvature for females. The consistency of hair diameter within individuals was also highly heritable (68%) without sex differences. There were moderate phenotypic correlations between diameter and consistency (r = 0.3) but little correlation between diameter and curvature (r = -0.13). Genetic correlations between hair diameter and consistency were r gF = 0.27 for females and r gM = 0.25 for males.