Dave Sobszak, age 12, of Duluth, Minnesota, for his question:
Why do people have different colored hair?
Interest in this topic ranges all the way from the popular scene to the science lab. You might not expect serious researchers to concern themselves with the glamorous subject of human hair coloration. However, not one but several branches of biology are probing the problem
No girl is quite satisfied with the natural color of her hair or so it seems. The brunettes strive to be blondes and the blondes strive to be brunettes or redheads. Later in life, when the natural tints fade to greys, many women and some m®n set about restoring their hair with dye to the more youthful tints. At least, the commercials would have us think that this is so. On the popular scene, most of this interest is due to the worthy human impulse to improve on nature. Everyone wants to put the best foot forward to be a little better, act a little better and look a little better than nature intended. If this were not a strong human desire, mankind never would have become half civilized.
When Caesar reached the British Isles, he found Celtic people with their skins painted blue and their naturally dark hair bleached blonde. So man's interest in hair coloration is not new. Modern science, however, is interested in the subject from a different point of view: Researchers know a lot about why people°inherit coloration from their ancestors. They also know a lot about the factors that cause various colorations in the skin and hair. They have good reasons for wanting to know more.
The pigment that colors the hair is called melanin, and it is the same chemical that masks the skin with matching, tones of beige, brown or black. Biologists have discovered that melanin is created when a chemical called tyrosinase oxidizes with a chemical called tyrosine. Tyrosinase is one of the body's enzymes; tyrosine is one of its basic amino acids.
The pigment is made in melanocyte cells embedded in the living layer of skin below the papery surface. All melanin is dark brown and everyone has about the same number of melanocytes. But production varies from person to person. A dark person's melanocytes teem with dark granules, a redhead does not have as many and a blonde has still fewer. Each single hair is a shaft of pale dead cells fzrowing from a living root that supplies it with oil and a share of the body's normal melanin quota. Lots of melanin colors the hair dark, a smaller amount adds a rusty red tint. A natural blonde has just enough melanin granules to tinge the hair shaft with yellow. The same pigment also tints the skin, masking its bare pink color. A person's melanin quota decides the hair color and adds a dark or light complexion to match it.
Your melanin quota is dictated by a unique body building blueprint inherited from a long string of ancestors. Geneticists are interested in all such inherited characteristics. Others are interested in the melanin quota of dark and light races and also in the rare albino individuals that have no melanin at all. Others wonder how sunshine causes extra melanin to tan the skin. And most of them suspect that a bountiful quota of the dark pigment helps to screen out harmful ultraviolet rays.