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Hair Identification
Animal Versus Human Hairs
Human hairs are distinguishable from hairs of other mammals.
Animal Hairs
Animal hairs are classified into the following three basic types:
- Guard hairs that form the outer coat of an animal and provide protection
- Fur or wool hairs that form the inner coat of an animal and provide insulation
- Tactile hairs (whiskers) that are found on the head of animals provide sensory functions
Other types of hairs found on animals include tail hair and mane hair (horse). Human hair is not so differentiated and might be described as a modified combination of the characteristics of guard hairs and fur hairs.
Human Hairs
Human hairs are generally consistent in color and pigmentation throughout the length of the hair shaft, whereas animal hairs may exhibit radical color changes in a short distance, called banding. The distribution and density of pigment in animal hairs can also be identifiable features. The pigmentation of human hairs is evenly distributed, or slightly more dense toward the cuticle, whereas the pigmentation of animal hairs is more centrally distributed, although more dense toward the medulla.
The medulla, when present in human hairs, is amorphous in appearance, and the width is generally less than one-third the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and generally occupies an area of greater than one-third the overall diameter of the hair shaft.
The root of human hairs is commonly club-shaped, whereas the roots of animal hairs are highly variable.
The scale pattern of the cuticle in human hairs is routinely imbricate (overlapping). Animal hairs exhibit more variable scale patterns. The shape of the hair shaft is also more variable in animal hairs.
Caucasoid (European Ancestry)
- Caucasoid or Caucasian Origin
Hairs of Caucasoid or Caucasian origin can be of fine to medium coarseness, are generally straight or wavy in appearance, and exhibit colors ranging from blonde to brown to black. The hair shafts of Caucasian hairs vary from round to oval in cross section and have fine to medium-sized, evenly distributed pigment granules.
Caucasian or European Hair on Microscope Slide
Mongoloid (Asian Ancestry)
- Mongoloid or Asian Origin
Hairs of Mongoloid or Asian origin are regularly coarse, straight, and circular in cross section, with a wider diameter than the hairs of the other racial groups. The outer layer of the hair, the cuticle, is usually significantly thicker than the cuticle of Negroid and Caucasian hairs, and the medulla, or central canal, is continuous and wide. The hair shaft, or cortex, of Mongoloid hair contains pigment granules that are generally larger in size than the pigment granules of Caucasian hairs and which often appear to be grouped in patchy areas within the shaft. Mongoloid hair can have a characteristic reddish appearance as a product of its pigment.
Mongoloid or Asian Hair on Microscope Slide
Negroid (African Ancestry)
- Negroid or African Origin
Hairs of Negroid or African origin are regularly curly or kinky, have a flattened cross section, and can appear curly, wavy, or coiled. Negroid pigment granules are larger than those found in Mongoloid and Caucasian hair and are grouped in clumps of different sizes and shapes. The density of the pigment in the hair shaft may be so great as to make the hair opaque. A Negroid hair shaft exhibits variation or apparent variation in diameter because of its flattened nature and the manner in which it lies on the microscope slide. Twisting of the hair shaft, known as buckling, can be present, and the hair shaft frequently splits along the length.
Negroid or African Hair on Microscope Slide
References:
1) U.S. Department of Justice - Federal Bureau of Investigation - Forensic Science Communications - July 2000 - www.fbi.gov
2) Forensic Science Communications - January 2004 - www.fbi.gov
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