According to: http://www.howstuffworks.com/question100.htm Each hair on your body grows from its own individual hair follicle. Inside the follicle, new hair cells form at the root of the hair shaft. As the cells form, they push older cells out of the follicle. As they are pushed out, the cells die and become the hair we see. A follicle will produce new cells for a certain period of time depending on where it is located on your body. This period is called the growth phase. Then it will stop for a period of time (the rest phase), and then restart the growth phase again. When the hair follicle enters the rest phase, the hair shaft breaks, so the existing hair falls out and a new hair takes its place. Therefore, the length of time that the hair is able to spend growing during the growth phase controls the maximum length of the hair. The cells that make the hairs on your arms are programmed to stop growing every couple of months, so the hair on your arms stays short. The hair follicles on your head, on the other hand, are programmed to let hair grow for years at a time, so the hair can grow very long. ===== Hope this helps.

How fast does a male's hair grow, in inches in a month?

You should talk to my wife who seems to think that after the age 30 men tend to stop growing hair on their heads and start growing it everywhere else on their bodies!! :)

Evolution has taught our bodies that we don't need much hair on our bodies to keep our body temperature normal because we now wear a substitute in the form of clothes. (well most of us do) However, the hair on our head not only helps keep warmth in but it is often an important part of sexual attraction. Two beautiful heads of hair will likely produce a child with a beautiful head of hair.

WILD GUESS: Isn't part of the function of hair the warmth it provides? It preserves heat that would otherwise have escaped through our scalp. Mammals grow hair to protect the skin and conserve heat; the head is a crucial part of the body to keep warm. Humans are maybe in less danger of losing heat through the skin for various physiological reasons, which is why we have less hair than other mammals. But technically we grow hair everywhere except for our palms and a few tiny body parts like eyelids. How much hair we have seems to depend on hormones (like how people with testosterone grow hair on their chin/face). I wonder if it also maybe depends on how much danger we are of losing heat. Are people from the north more hairy? Are we less hairy than we were thousands of years ago when we started wearing clothes? Anyway- to keep the head warm, is my guess, as an evolutionary reason for the physical mechanism Singwell describes.

As an animal, man is a runner. He's not particularly fast, but he his good at long distance running. The current thinking is that before settling down and farming, man would generally run down his prey by causing them to overrun for their hairy bodies. Before we used spears or whatever, just the scent of [predator] man would scare animals, and they'd run. But most animals, particularly furred creatures can only run so far before they collapse from exhaustion or their heart explodes. Because of reduced body hair, man can run much further making him an extremely effective hunter (80-90% compared to other predators at about 20%). So, man evolved from predators that were selected for distance running From an upright posture and predominantly hairless skin, the only thing that needs hair are the areas generally exposed straight up - ie to the sun. So the top of the head retains a full mane. The other pubic regions retain hair because they are important scent production zones. Armpits and the hair above the ears produce the most amount of scent. This is the predatorial scent that keeps animals running rather than hiding. Pubic region hair might also be for predation scent, but might also be more of a mating issue. It's likely that male facial hair is a cold-weather retention so that the body could be wrapped with furs until it was time to run, but the face would stay warm at all times.