Page 51 - Cosmetology

upright posture. There are several problems with this theory, not least of which is that
cursorial hunting is used by other animals that do not show any thinning of hair.

Another theory for the thin body hair on humans proposes that Fisherian runaway sexual
selection played a role here (as well as in the selection of long head hair). Possibly this
occurred in conjunction with neoteny, with the more juvenile appearing females being

selected by males as more desirable; see types of hair and vellus hair.

The Aquatic Ape Hypothesis posits that sparsity of hair is an adaptation to an aquatic
environment, but it has little support amongst scientists and very few aquatic mammals
are, in fact, hairless.

In reality, there may be little to explain. Humans, like all primates, are part of a trend
toward sparser hair in larger animals; the density of human hair follicles on the skin is

actually about what one would expect for an animal of our size. The outstanding question
is why so much of human hair is short, underpigmented vellus hair rather than terminal
hair.

Head hair

The most noticeable part of human hair is the hair on the head, which can grow longer
than on most mammals and is more dense than most hair found elsewhere on the body.
The average human head has about 100,000 hair follicles. Its absence is termed alopecia,
commonly known as baldness. Anthropologists speculate that the functional significance

of long head hair may be adornment, a byproduct of secondary natural selection once
other somatic hair had been lost. Another possibility is that long head hair is a result of
Fisherian runaway sexual selection, where long lustrous hair is a visible marker for a

healthy individual (with good nutrition, waist length hair—approximately 1 meter or 39
inches long—would take around 80 months, or just under 7 years, to grow). This would
explain why long head hair (in both sexes) is viewed as attractive even now.

Types of hair