Physicians have always been confronted with life-and-death choices—having to make difficult decisions is part of the responsibility of being a doctor. But the predicaments that doctors find themselves in today are the subject of more interest and controversy than ever before, simply because advances in modern medicine over the past few decades have given rise to situations that no one would have expected in an earlier era.

Consider this scenario: A woman, heartbroken over her husband’s death, chooses to have his memory live on in the form of a son. She pays to have fertility doctors, using cloning techniques and in vitro fertilization, impregnate her with an embryonic clone of her deceased husband. She gives birth to his genetic twin nine months later. Should fertility doctors be allowed to offer this type of service"

This scenario, of course, is entirely hypothetical. Scientists are not...