Variation in Human Hair Morphology and Microstructure

Open Access
- Author:
- Koch, Sandra Lynn
- Graduate Program:
- Anthropology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 07, 2018
- Committee Members:
- Nina G Jablonski, Dissertation Advisor/Co-Advisor
Nina G Jablonski, Committee Chair/Co-Chair
Mark Shriver, Committee Member
Timothy Michael Ryan, Committee Member
Joy Lee Pate, Outside Member
philip reno, Committee Member - Keywords:
- hair
microscopical analysis
forensic
anthropology
TEM - Abstract:
- Human hair varies considerably in form and color within an individual and among groups. I examined diversity within human hair, and conducted tests to determine the nature and pattern of differences in the size and shape of hair and the density and distribution of pigment granules (melanosomes). Differences in hair form and cuticle thickness are apparent between broadly defined geographic ancestry groups, but these categories do not necessarily reflect our modern, genetically admixed world. Using Transmission Electron Microscopy (TEM), I investigated the degree of cuticle variability within the hairs from individuals, hairs from peoples who shared similar ancestry, and among people with diverse ancestries. Measurable differences were found in cuticle thickness and in the number of cuticle layers among the populations studied. Hairs from people with African ancestry tend to have thinner cuticles with fewer layers making up the cuticle, while those from people of European and East Asian ancestry tend to have thicker cuticles made up of more layers. Samples of hairs from peoples of European and East Asian ancestry are not statistically significant in cuticle thickness and in the number of layers. Testing European and East Asian hairs against African hairs show statistically significant differences in the cuticle thickness and number of layers. Variation exists within and among human populations in hair color, degree of curl, cross-sectional shape, diameter, and length. Analyses of hair dimensions and the number and distribution of pigment particles within a hair cross section revealed variability among diverse populations, and demonstrated that hair traits are not easily separable into distinct categories by ancestry. These findings offer support for eliminating the use of the outdated three-category racial typologies used by many U.S.-trained forensic scientists. I observed general trait patterns that may be useful for future research and that point to the need for additional research on the effects of genetic admixture to better assess ancestry traits in human hair.