Cigar, the champion racehorse, is a dud as a stud. Attempts to impregnate numerous mares have failed. But his handlers are not discouraged. They think they might try to have Cigar cloned.

If a sheep and a monkey can be cloned—and possibly a racehorse—can human clones be far behind? The process is novel, though the concept is not.

We have long known that virtually every cell of the body contains a person's complete genetic code. The exception is sperm or egg cells, each of which contains half the genetic material until the sperm fertilizes the egg and a new human being with a complete genetic code begins growing.

We have now learned that the partial genetic material in an unfertilized egg cell may be replaced by the complete genetic material from a cell taken from an adult. With a full genetic code, the egg cell behaves as if it has been fertilized. At least, that is how Dolly, the sheep cloned in Scotland, came to be. Hence, producing genetic copies of human beings now seems more likely.

We have been anticipating this possibility in humans for decades and have been playing with it in our imaginations. The movie The Boys from Brazil was about an attempt to clone Adolf Hitler. And in Aldous Huxley's novel Brave New World, clones were produced to fulfill undesirable social roles. More recently the movie Multiplicity portrayed a harried man who jumped at the chance to have himself copied—the better to tend to his office work, his home chores, and his family relationships. It all seems so attractive, at first glance, in our hectic, achievement-crazed society.

The costs of clones But how do we achieve this technologically blissful state? Multiplicity is silent on this matter, implying that technique is best left ...