Why Mammal Body Hair Is an Evolutionary Enigma

*Jerry Bergman, Ph.D., Northwest State College 22-600 State Rt 34, Archbold, OH 43543 Received April 4, 2003; Revised October 13, 2003 Mammal body hair is a complex structure that involves several basic parts, including a shaft, a root, and a follicle. The most common theory currently in vogue is that hair evolved from reptile scales. Although both scales and hair preserve well in the fossil record, especially in amber, no evidence of hair evolution has been found after more than a century of searching. Another problem is that all primates have thick, coarse hair called fur, and explanations as to how this fur was lost in human evolution are deficient and contradictory. the body can use to produce heat. The muscle contraction produces the familiar “goose bumps” that result from cold temperatures, embarrassment, or fear (and is an important means of communication both to one’s self and to others). Located in the hair root, the external root sheath contains all the epidermal strata existing in normal skin. If the epidermis and superficial part of the dermis are damaged, the undamaged part of the hair follicle (which is protected because it lies deep with in the dermis) is a source of new epithelium to repair surface skin damage (Seeley et al., 2003). Each hair shaft has an inner layer of cells called the medulla or pith, containing soft keratin and shrunken cells of dried epithelial structures. The next layer is called the cortex, which is a semi-transparent, thick layer that contains “hard type keratin” filled cells (Seeley et al., 2003). It occupies the bulk of the hair. The cortex contains scattered pigment cells that produce melanin, giving hair its color. Color is an important tool used to differentiate hair for both biological research studies and forensic work (Saferstein, 2002). The outer layer of the hair shaft, the cuticle, consists of a single layer of colorless keratinized cells that cover the hair somewhat like skin. These hardened, flat cells overlap like house shingles and are arranged “in an imbricate fashion and often beautifully sculptured” (Hamilton, 1939, p. 69). The ends of the flat cells always point toward the tip of the hair, not the hair root (Saferstein, 2002).