THE IDEA OF cloning was around long before Dolly—in fact, cloning has been done for centuries. Until fairly recently, however, all cloning was done with plants, not with animals. Cloning was a way for farmers and other plant growers to give a boost to nature and make their own jobs easier.

Cloning flowers

Plant breeders have been taking advantage of the predictability of cloning for a long time. They know they are going to get a perfect copy of the plant or animal they started with: the clone will have exactly the same genes as the original. This predictability can be a great benefit in many fields.

Consider the business of growing flowers. For example, a field of chrysanthemum plants grown from seed is vulnerable in many ways. The plants can be...