Steve Griffin, age 12, of Gastonia, NorthCarolina, for his question:

Why do eyelashes grow only so lone?

If eyelashes grew as long as the hair on our heads, we would be fumbling around in the dark. Or, we could make regular visits to barbers or hairdressers to have them cut and shaped. However, there is no need to worry about this nonsense because, as you know, eyelashes grow only so long. Like other hairs, they are always growing, old ones fall out and new ones grow in to replace them. The average life expectancy of an eyelash hair is about three months.

The reason they stay so neatly in bounds is related to the miraculous pockets of cells that create them. These root hairs, like all other cells in the body, are programmed by one's personal DNA. This remarkable biochemical directs every procedure in every cell in the body. It dictates exactly how each root hair shall build an eyelash and exactly how long to make it. Fortunately, DNA sets a comfortable limit on the length of human eyelashes.