Chapter 8 Hairs & fibers Hair anatomy 1 Hair forensics • Hair shaft – Cuticle – Cortex – Medulla Hair cuticles • Scale patterns vary by species Human Cat Otter 2 Hair cortex • Pigment granules – Color, shape distribution Eumelanin is the dark pigment which predominates in black and brunette hair. Phaeomelanin is a lighter pigment, which is found in red and blond hair Hair cortex 3 Hair medulla • Vary by species • Medullary index (diameter of medulla/ diameter of hair shaft) – Humans <0.33 – Animals >0.5 Hair medulla • Medulla patterns vary by individual hairs and by species (fragmented) (interrupted) 4 Hair root growth phases • Phase of growth – Anagen – follicle actively producing hair – Telogen – Growth ends, hair shed in 2-6 mos. Hair root 5 Distinguishing human hairs • Racial origins Distinguishing human hairs • Body location Limb – fragmented/trace medulla Beard – double medulla Pubic – continuous medulla 6 Distinguishing human hairs • Body location Misc. hair characteristics Lice egg sac Dyed 7 Hair microscopy There are three basic conclusions that can be reached from a microscopic examination and comparison of hairs: • The hairs from the questioned (Q) source exhibit the same microscopic characteristics as the hairs in a known (K) hair sample and can be associated to the source of the known hairs. • The hairs from the questioned source are microscopically dissimilar to the hairs in a known hair sample and cannot be associated with the source of the known hairs. • The questioned hairs exhibit both similarities and slight differences to hairs found in a known hair sample, and no conclusion can be reached whether they could have originated from the known source. It may be that, in the opinion of the examiner, the differences are not sufficient to eliminate the source of the known hairs as being a possible source of the questioned hairs. At the same time, the presence of these differences precludes an association being made between the questioned and known hairs. Online Hair resources • Microscopy of Hair Part 1: A Practical Guide and Manual for Human Hairs – http://www.fbi.gov/hq/lab/fsc/backissu/jan2004 /research/2004_01_research01b.htm 8