Quantifying variation in human scalp hair fiber shape and pigmentation.

OBJECTIVES This study aims to evaluate the use of quantitative methods of measuring variation in scalp hair fiber shape and pigmentation and carry out exploratory data analysis on a limited sample of individuals from diverse populations in order to inform future avenues of research for the evolution of modern human hair variation. METHODS Cross-sectional area and shape and average curvature of scalp hair fibers were quantified using ImageJ. Pigmentation was analyzed using chemical methods estimating total melanin content through spectrophotometric methods, and eumelanin and pheomelanin content through HLPC analysis of melanin-specific degradation products. RESULTS The initial results reinforced findings from earlier, traditional studies. African and African Diaspora scalp hair was significantly curled, (East) Asian hair was significantly thick, and European hair was significantly lighter in color. However, pigmentation analyses revealed a high level of variability in the melanin content of non-European populations and analysis of curvature found a large range of variation in the average curvature of East African individuals. CONCLUSIONS Overall, these results suggest the usefulness of chemical methods for the elucidation of nonperceptible differences in scalp hair color and highlight the need for improvements in our assessment and understanding of hair fiber curvature. Am J Phys Anthropol 160:341-352, 2016. © 2016 Wiley Periodicals, Inc.

[1]  D. Duffy,et al.  Spectrophotometric Methods for Quantifying Pigmentation in Human Hair—Influence of MC1R Genotype and Environment , 2008, Photochemistry and photobiology.

[2]  F. Leroy,et al.  Current research on ethnic hair. , 2003, Journal of the American Academy of Dermatology.

[3]  D. Absher,et al.  Genome-Wide Association Studies of Quantitatively Measured Skin, Hair, and Eye Pigmentation in Four European Populations , 2012, PloS one.

[4]  P. Frost.  European hair and eye color: A case of frequency-dependent sexual selection? , 2006 .

[5]  K. Wakamatsu,et al.  Spectrophotometric characterization of eumelanin and pheomelanin in hair. , 1996, Pigment cell research.

[6]  F. Leroy,et al.  Human hair keratin network and curvature , 2007, International journal of dermatology.

[7]  M. Dixon,et al.  Enhanced ectodysplasin‐A receptor (EDAR) signaling alters multiple fiber characteristics to produce the East Asian hair form , 2008, Human mutation.

[8]  B. Forslind,et al.  Human hair form. Morphology revealed by light and scanning electron microscopy and computer aided three-dimensional reconstruction. , 1988, Archives of dermatology.

[9]  C. Mulligan,et al.  Early Back-to-Africa Migration into the Horn of Africa , 2014, PLoS genetics.

[10]  J. Thompson,et al.  The cross–sectional size and shape of human terminal scalp hair , 1997, The British journal of dermatology.

[11]  M. Brilliant,et al.  Usefulness of alkaline hydrogen peroxide oxidation to analyze eumelanin and pheomelanin in various tissue samples: application to chemical analysis of human hair melanins , 2011, Pigment cell & melanoma research.

[12]  J. Gillespie,et al.  Influence of nutrition on the crimping rate of wool and the type and proportion of constituent proteins. , 1975, Australian journal of biological sciences.

[13]  I. Jackson,et al.  Pleiotropic effects of the melanocortin 1 receptor (MC1R) gene on human pigmentation. , 2000, Human molecular genetics.

[14]  K. Wakamatsu,et al.  Diversity of human hair pigmentation as studied by chemical analysis of eumelanin and pheomelanin , 2011, Journal of the European Academy of Dermatology and Venereology : JEADV.

[15]  K. Wakamatsu,et al.  The usefulness of 4-amino-3-hydroxyphenylalanine as a specific marker of pheomelanin. , 2002, Pigment cell research.

[16]  Li Jin,et al.  Modeling Recent Human Evolution in Mice by Expression of a Selected EDAR Variant , 2013, Cell.

[17]  Manuel A. R. Ferreira,et al.  Common variants in the trichohyalin gene are associated with straight hair in Europeans. , 2009, American journal of human genetics.

[18]  B. Bernard.  Hair shape of curly hair. , 2003, Journal of the American Academy of Dermatology.

[19]  S. Thibaut,et al.  Human hair shape is programmed from the bulb , 2005, The British journal of dermatology.

[20]  Jonathan Scott Friedlaender,et al.  Skin and hair pigmentation variation in Island Melanesia. , 2006, American journal of physical anthropology.

[21]  T. Tsunoda,et al.  A replication study confirmed the EDAR gene to be a major contributor to population differentiation regarding head hair thickness in Asia , 2008, Human Genetics.

[22]  T. Kupiec,et al.  Association of the SLC45A2 gene with physiological human hair colour variation , 2008, Journal of Human Genetics.

[23]  M. Trotter.  A review of the classifications of hair , 1938 .

[24]  R. Sturm,et al.  Molecular genetics of human pigmentation diversity. , 2009, Human molecular genetics.

[25]  J. Bartko.  The Intraclass Correlation Coefficient as a Measure of Reliability , 1966, Psychological reports.

[26]  Y. Amemiya,et al.  Structural analysis of human hair single fibres by scanning microbeam SAXS. , 2006, Journal of structural biology.

[27]  J. Relethford,et al.  Human skin color diversity is highest in sub-Saharan African populations. , 2000, Human biology.

[28]  G. Piérard,et al.  Mechanobiology and cell tensegrity: the root of ethnic hair curling? , 2011, Journal of cosmetic dermatology.

[29]  J. Fleiss,et al.  Intraclass correlations: uses in assessing rater reliability. , 1979, Psychological bulletin.

[30]  K. Wakamatsu,et al.  Age‐dependent changes in eumelanin composition in hairs of various ethnic origins , 2012, International journal of cosmetic science.

[31]  D. G. Vernall.  A study of the size and shape of cross sections of hair from four races of men. , 1961, American journal of physical anthropology.

[32]  Jonathan Scott Friedlaender,et al.  Distribution of an allele associated with blond hair color across Northern Island Melanesia. , 2014, American journal of physical anthropology.

[33]  Kevin A Hallgren,et al.  Computing Inter-Rater Reliability for Observational Data: An Overview and Tutorial. , 2012, Tutorials in quantitative methods for psychology.

[34]  Pardis C Sabeti,et al.  The adaptive variant EDARV370A is associated with straight hair in East Asians , 2013, Human Genetics.

[35]  Jonathan Scott Friedlaender,et al.  MC1R diversity in Northern Island Melanesia has not been constrained by strong purifying selection and cannot explain pigmentation phenotype variation in the region , 2015, BMC Genetics.

[36]  D Hrdy,et al.  Quantitative hair form variation in seven populations. , 1973, American journal of physical anthropology.

[37]  Richard Hodgson,et al.  Single nucleotide polymorphisms in the MATP gene are associated with normal human pigmentation variation , 2005, Human mutation.

[38]  J. Caldwell,et al.  Cortical cell types and intermediate filament arrangements correlate with fiber curvature in Japanese human hair. , 2009, Journal of structural biology.

[39]  D. Duffy,et al.  Linkage and association analysis of spectrophotometrically quantified hair color in Australian adolescents: the effect of OCA2 and HERC2. , 2008, The Journal of investigative dermatology.

[40]  Maido Remm,et al.  Population genetic structure in Indian Austroasiatic speakers: the role of landscape barriers and sex-specific admixture. , 2011, Molecular biology and evolution.

[41]  Snæbjörn Pálsson,et al.  Genetic determinants of hair, eye and skin pigmentation in Europeans , 2007, Nature Genetics.

[42]  Katsushi Tokunaga,et al.  A scan for genetic determinants of human hair morphology: EDAR is associated with Asian hair thickness. , 2008, Human molecular genetics.

[43]  J. Rees.  Genetics of hair and skin color. , 2003, Annual review of genetics.

[44]  C. Bustamante,et al.  Melanesian Blond Hair Is Caused by an Amino Acid Change in TYRP1 , 2012, Science.

[45]  E. M. Wynkoop.  A study of the age correlations of the cuticular scales, medullas, and shaft diameters of human head hair , 1929 .

[46]  G. Loussouarn,et al.  Worldwide diversity of hair curliness: a new method of assessment , 2007, International journal of dermatology.

[47]  André Langaney,et al.  Shape Variability and Classification of Human Hair: A Worldwide Approach , 2007, Human biology.