transferred from an individual to the crime scene, and from the crime scene to an individual. Forensic hair examiners generally recognize that various physical characteristics of hairs can be identified and are sufficiently different among individuals that they can be useful in including, or excluding, certain persons from the pool of possible sources of the hair. The results of analyses from hair comparisons typically are accepted as class associations; that is, a conclusion of a “match” means only that the hair could have come from any person whose hair exhibited—within some levels of measurement uncertainties—the same microscopic characteristics, but it cannot uniquely identify one person. However, this information might be sufficiently useful to “narrow the pool” by excluding certain persons as sources of the hair.
Although animal hairs might provide useful evidence in certain cases (e.g., animal poaching), animal hair analysis often can lead to an identification of only the type of animal, not the specific breed66; consequently, most (90 to 95 percent) of hair analyses refer to analyses of human hair. Human hairs from different parts of the body have different characteristics; Houck cautions strongly against drawing conclusions about hairs from one part of the body based on analyses of hairs from a different body part.67
Houck and Bisbing recommend as minimal training for hair examiners a bachelor’s degree in a natural or applied science (e.g., chemistry, biology, forensic science), on-the-job training programs, and an annual proficiency test.68
Sample hairs received for analysis initially are examined macroscopically for certain broad features such as color, shaft form (e.g., straight, wavy, curved, kinked), length, and overall shaft thickness (e.g., fine, medium, coarse).
In the second stage of analysis, hairs are mounted on microscopic slides using a mounting medium that has the same refractive index (about 1.54) as the hair, to better view the microscopic features (see next section). One hair or multiple hairs from the same source may be mounted on a glass microscope slide with an appropriate cover slip, as long as each mounted hair is clearly visible. It is most important that questioned and known hairs are mounted in the same type of mounting medium.
During this examination, the hair analyst attempts to identify the part of the body from which the hair might have come, based on certain de-