WHEN THE CLONING of Dolly the sheep was announced to the world, a new question arose in people's minds: If it is true after all that an adult mammal can be cloned, does this mean that human beings, too, can be cloned"

The answer, according to many scientists, is probably yes. "There is no reason in principle why you couldn't do it," says Ian Wilmut, the scientist who cloned Dolly. But scientists attempting to clone human beings would encounter some problems that Ian Wilmut did not have to deal with.

The basic steps

Ian Wilmut started his cloning experiment with udder cells from one sheep and an egg (with its genetic material removed) from another sheep. He put the genetic material from the cells into the egg, gave the egg a small jolt of electricity, and it began to divide and become...