THE SCIENCE:
Five years ago, scientists took a cell from a sheep, implanted it into an empty egg and coaxed it to divide as a normal embryo. A perfect genetic copy, Dolly, was the result. But there is some evidence that Dolly aged prematurely. Other clones, from mice to cows, have also proved abnormal.
THE ETHICS:
Twins and even triplets have been around for millenniums, but engineering multiple copies of an adult or a lost child is just too creepy.