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Untangling a Hair-y Science

Sandra Koch, PhD

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What’s so special about hair?

Hair is one of the defining features of mammals

– Protection

– Thermoregulation

– Tactile sense

– Cultural identity

– Signaling

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What’s so special about hair?

Hair is one of the defining features of mammals

– Protection

– Thermoregulation

– Tactile sense

– Cultural identity

– Signaling

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Who studies hair?

• Forensic Scientists

• Anthropologists

• Geneticists

• Biologists

• Cosmetic Industry

• Mammologists

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Sample Preparation

Light microscopy

• Mounting medium needed

– Air or water alone doesn’t work so well

Scale casts

• Nail polish : acetone

• Glue : water

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Microscopical Hair Analysis

• Is it a hair?

• Human or non-human?

• Can body area be determined?

• Are there features useful for estimating ancestry or species?

• Any characteristics of disease, damage, chemical alteration, or decomposition?

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Non-human Mammalian Hair3 Types:Whiskers – sensoryGuard Hairs – protection and camouflage (can be morphologically differentiated among animal families)Underfur – insulation

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Human Hairhead, pubic, facial, axillary, chest, limb, and eye

Head and pubic hair are suitable for microscopical

comparison

Head

Eyelash

LimbPubic

Facial

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How Hair Grows

• Timing (seasonal vs asynchronous)

• Growth cycle and rate

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Morphology

Human Hairs Non-human Hairs

This

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Microstructure

Deedrick, Douglas W., and Sandra L. Koch. "Microscopy of hair part II: a practical guide and manual for animal hairs." Forensic Science Communications 6.3 (2004).

Dog Hair

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Microstructure

• Medulla

• Pigment distribution

• Color

• Cuticle

furCat fur

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Hair Pigmentation

• Humans:

– pigment granules distributed toward cuticle

– no banding

• Non-human mammals:

– pigment granules distributed toward medulla

– can be banded

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Electron Microscopy

SEM TEM

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Transmission Electron Microscopy

• Ultrastructure

– Cuticle layers, melanosomes, cortical cells, etc.

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Damage or Alteration

• Dyed or bleached

• Decomposition

• Insect bites

• Fungal tunneling

Tridico, Silvana R., et al. "Interpreting biological degradative processes acting

on mammalian hair in the living and the dead: which ones are

taphonomic?." Proceedings of the Royal Society of London B: Biological Sciences 281.1796 (2014): 20141755.

Image credits:

Deedrick, Douglas W., and Sandra L. Koch. "Microscopy of hair part 1: a

practical guide and manual for human hairs." Forensic Science Communications 6.1 (2004).

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Ancestry

• Cross-sectional shape

• Diameter

• Cuticle thickness

• Pigment patterns

• Degree of curl

How reliable are these traits?

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Old Terminology:

Scientifically Invalid

Racial

classifications

Caucasoid

Negroid

Mongoloid

Typological model fails

because most biological traits are continuous variables.

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Resource Guidelines

• SWGMAT guidelines

http://www.asteetrace.org/WebPages.cfm?action=viewCat&BIZ_UNL_id=41614

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Training

• Hooke College of Applied Sciences Hair Course

• Benefits:

– Practical exercises

– Interaction with scientists from different laboratories

– Extensive training samples associated with known ancestry and from a variety of identified species

– Ability to start building your reference collection

– Discussions on report writing and significance

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Questions?

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https://www.zmescience.com/oth

er/feature-post/why-we-get-

goosebumps/

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%D0%A4%D0%B0%D0%B9%

D0%BB:Whiskers.jpg

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g/wiki/File:Arctic_Foxes_(8154

290495).jpg

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Att%C4%93ls:Arcticfox-3.jpg

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iki/File:Cheshin_and_Shapiro.jpg

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e/foto/augen-bezaubernd-

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ca-Wild-Animal-Cat-Predator-

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-us/lab/forensic-science-

communications/fsc/jan2

004/research/2004_01_r

esearch01b.htmhttps://commons.wikimedia.org/wiki/File:Red_hair_close_up_wavy.jpg

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gouti_(coloration)

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20/brown-rabbits/

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http://www.personal.psu.edu/users/c/l/clv14/

sci101/hair.htm

Image Attributions