Evidence Is hair Class or Individual evidence HAIR

Evidence • Is hair – Class or – Individual evidence?

HAIR • ~5 million on human • Head hair – Blondes have ~120 k – Brunettes have ~100 k – Redheads have ~80 k • Continuously shed and replaced at 100/d

Form and Structure • Made of cross-linked protein polymers • Grows from follicle • Linked to body’s blood supply – Drugs and poisons will show up • Cuticle – overlapping scales • Cortex – keratin; pigment • Medulla

Form and Structure, cont.

Cuticle • Outermost layer • Dead, translucent cells • Scale pattern • Differs between animal species

Cortex • Keratin • Color determined by – Amount and – Type of melanin • Brown or black = high conc. of melanin • Blonde or red = low conc. of melanin • Gray/white = no melanin • Humans – melanin density/distribution even • Other animals – more dense toward medulla; may be banding

Medulla • Central layer or core (when present); a row of cells like a canal • Three possible patterns – – Continuous Interrupted Intermittent (segmented) or absent • Differences between species

Humans vs. Other Animals • Human hair – usually imbricate cuticle • Other animals – coronal or spinous cuticle • Other animals – 3 different hair types – Guard – outer coat; coarse, straight, taper – Ground (underfur) – fine, soft, kinked; if matted = wool – Whiskers – long, thick, stiff

More… • Shapes – Round (Asian) – Oval (Caucasoid) – Flattened (Negroid) • Roots – Flame-shaped - growth phase; if forcibly removed, has tissue – rich DNA source – Elongated - Growth slowed – Club-shaped – final phase

Tips • Tip of a mature human hair – Tapers to a point if not cut recently – Squared off if recently cut – Rounded end within 23 weeks of cutting – Frayed hair or split ends from dryness, harsh chemicals, too much blow drying