why do humans have pubic hair?

Answer 1

Pubic hair is hair in the frontal genital area, the crotch, and sometimes at the top of the inside of the legs; these areas form the pubic region. Although fine vellus hair is present in the area in childhood (and sometimes can be wierd colours such as red and blue), the term pubic hair is generally restricted to the heavier, longer hair that develops with puberty as an effect of rising levels of androgens. Pubic hair is therefore part of the androgenic hair.

Androgen is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of masculine characteristics in vertebrates by binding to androgen receptors. This includes the activity of the accessory male sex organs and development of male secondary sex characteristics. Androgens, which were first discovered in 1936, are also called androgenic hormones or testoids. Androgens are also the original anabolic steroids. They are also the precursor of all estrogens, the female sex hormones. The primary and most well-known androgen is testosterone.

For more information on pubic hair, its history, development and affect read on:

http://en.wikipedia.org/wiki/Pubic_hair

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Answer 2

Why do we have hair anywhere else? Because we're mammals. Hair serves to help regulate temperature (the orientation of the hair follicles changes depending on whether the body want to trap heat or release it), and is protective. The coarse hair on the head and genital area (and face and chest in males) helps to keep sun, dirt, and other irritants off the skin.