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Untangling the Relationship between Hair Microstructure and Ancestry

Untangling the Relationship between Hair Microstructure and Ancestry. Sandra Koch. Human Variation: Hair. Does human scalp hair vary among population groups? H ow do we quantify trait variation for forensic purposes? Morphology (cross-sectional shape, dimensions, curl)

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Untangling the Relationship between Hair Microstructure and Ancestry

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  1. Untangling the Relationship between Hair Microstructure and Ancestry Sandra Koch

  2. Human Variation: Hair Does human scalp hair vary among population groups? How do we quantify trait variation for forensic purposes? • Morphology (cross-sectional shape, dimensions, curl) • Microstructure (pigmentation, cuticle, cortex, medulla) • Assessments by trained hair examiners http://zenzele.us/wp-content/uploads/2014/07/curl_pattern.jpg

  3. Old Terminology: Scientifically Invalid Racial classifications Caucasoid Negroid Mongoloid https://1.bp.blogspot.com/-WoF7De13c0g/TgZqPEmMm-I/AAAAAAAAARc/Qn1-f5xr8_8/s1600/mankind1ma6.jpg

  4. Old Terminology: Scientifically Invalid Typological model fails because most biological traits are continuous variables. Racial classifications Caucasoid Negroid Mongoloid

  5. Examiner Assessments of Ancestry

  6. Ellipticity Index Traits used in assessing ancestry 92.479 72.104 =1.28 • Cross-Sectional Shape: Elliptiticy • Size or Area of hair • Thickness of cuticle • Pigment size and distribution • Curl pattern 92.145 59.213 =1.56 126.55 70.536 =1.79

  7. Area =(0.5*max D)*(0.5*min D) *pi Traits used in assessing ancestry (0.5*92.479)*(0.5*72.104)*pi =5237 • Cross-Sectional Shape • Size or Area of hair • Thickness of cuticle • Pigment size and distribution • Curl pattern (0.5*92.145)*(0.5*59.213)*pi =4285 (0.5*126.55)*(0.5*70.536)+pi =7011

  8. Traits used in assessing ancestry • Cross-Sectional Shape • Size or Area of hair • Thickness of cuticle • Pigment size and distribution • Curl pattern

  9. Traits used in assessing ancestry • Cross-Sectional Shape • Size or Area of hair • Thickness of cuticle • Pigment size and distribution • Curl pattern

  10. Traits used in assessing ancestry • Cross-Sectional Shape • Size or Area of hair • Thickness of cuticle • Pigment size and distribution • Curl pattern Curly hair Mounted on slide https://www.lipstickalley.com/threads/kinky-vs-curly-whats-the-difference.563926/

  11. Hair Shape and Size Ellipticity Area Cross-sectional Shape Cross-sectional Area

  12. Cuticle Thickness European East Asian African

  13. Pigment Size African East Asian European 4200x TEM images

  14. Pigment Distribution % Area and clustering

  15. Hair Curl • Number of twists along length and apparent diameter changes Curly hair Mounted on slide https://www.lipstickalley.com/threads/kinky-vs-curly-whats-the-difference.563926/

  16. Examiner Assessments of Ancestry

  17. Admixed populations: problems with categorical race Hispanic Hair Samples Forensic Hair Examiner Responses

  18. Ancestry Reporting

  19. A Way Forward Possible report language: A human head hair microscopically dissimilar to the known head hair sample identified as representing person X was found in/on the submitted evidence. This hair is dark brown in color, has dense pigmentation, patterned in a clumpy distribution, a flattened ellipsoidal shape, thin cuticle, and a high degree of curl. Based on the microscopical and morphological characteristics observed, the hair traits are suggestive of a person with African ancestry; however, the amount of African ancestry is not known, and this assessment may not necessarily conform with how the individual self-identifies.

  20. Thank you • Funding support from: • NSF-NIJ grant (award 1453571) • ASTEE research award • Penn State Anthropology Dept. • Jablonski lab • Shriver lab

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