PROBLEMS AND ETHICS OF NUCLEAR TRANSPLANTATION
Cloning involves using genetic technology to make an exact genetic duplicate of an animal. Note that the new cloned animal starts out life as a single cell, develops into an embryo, and must proceed through childhood before becoming an adult. So although we can clone an animal, we do not get an instant full-grown duplicate.
So what about human cloning? The birth of Dolly the cloned sheep was followed by an outbreak of ethical discussion. Many critics insist that cloning humans is a threat to the sanctity of human life. In fact, human clones already exist. Identical twins, triplets, and so on are clones resulting from splitting of the same fertilized egg. Many ancient cultures regarded identical twins as supernatural in origin. Some cultures believed the twins were lucky; others thought they were evil and felt obliged to kill one of them.
Leaving aside moralistic arguments, there are major practical problems with cloning humans. The number of live clones born is just a few percent of the nuclei transplanted. Several lambs that died late in pregnancy or soon after birth were produced at the same time as Dolly, and some had developmental abnormalities. So cloning is fairly risky. Moreover, the chances of successful pregnancy, on implantation into a surrogate mother in humans, are estimated to be three- to 10-fold lower than in sheep. Thus the financial costs and effort to produce a cloned human would be vastly greater than for animals such as sheep. Outside of science fiction scenarios, why people would want to clone themselves is unclear. For one thing, the time scale of human development means that a cloned human duplicate would not be available for many years.