Within the first five years of the next century, a team of scientists somewhere in the world will probably announce the birth of the first cloned human baby. Like Louise Brown, the first child born as the result of in vitro fertilization 21 years ago, the cloned infant will be showered with media attention. But within a few years it will be just one of hundreds or thousands of such children around the world.

It has been possible to envision such a scenario realistically only since Ian Wilmut and his colleagues at the Roslin Institute near Edinburgh, Scotland, announced in February 1997 that they had cloned a sheep named Dolly from the udder cells of a ewe. The technique used by Wilmut and his co-workers--a technology called somatic-cell nuclear transfer--will probably be the way in which the first human clone will be created.

Although human cloning could generate a troop of people who look just like you, the clones won't be your age unless they were cloned right after you were conceived. They will still have to grow through childhood and adolescence to adulthood. The big question is: Will society regard them as separate individuals?

In somatic-cell nuclear transfer, researchers take the nucleus--which contains the DNA that comprises an individual's genes--of one cell and inject it into an egg, or ovum, whose own nucleus has been removed. The resulting embryo, which will carry the nucleus donor's DNA in every one of its cells, is then implanted into the womb of a female and carried to term.

Such research on the basic processes of cell differentiation holds out the promise of dramatic new medical interventions and cures. Burn victims or those with spinal cord injuries might be provided with replacement skin or nerve tissue grown from their own body cells. The damage done by degenerative disorders such as diabetes, Parkinson's disease or Alzheimer's disease might be reversed. In the more distant future, scientists might be able to grow whole replacement organs that our bodies will not reject.

These important medical uses of cloning technology urge us to be careful in our efforts to restrict cloning research. In the immediate wake of Dolly, politicians around the world proposed or implemented bans on human cloning. In the U.S., President Bill Clinton instituted a moratorium on federal funding for human cloning experiments, and the National Bioethics Advisory Commission urged that the ban be extended to private-sector research as well. Congress continues to study various proposals for enacting such a total ban.

In view of the still unknown physical risks that cloning might impose on the unborn child, caution is appropriate. Of the 29 early embryos created by somatic-cell nuclear transfer and implanted into various ewes by Roslin researchers, only one, Dolly, survived, suggesting that the technique currently has a high rate of embryonic and fetal loss. Dolly herself appears to be a normal three-year-old sheep--she recently gave birth to triplets following her second pregnancy. But a recent report that her telomeres--the tips of chromosomes, which tend to shrink as cells grow older--are shorter than normal for her age suggests that her life span might be reduced. This and other matters must be sorted out and substantial further animal research will need to be completed before cloning can be applied safely to humans.

Eventually animal research may indicate that human cloning can be done at no greater physical risk to the child than IVF posed when it was first introduced. One would hope that such research will be done openly in the U.S., Canada, Europe or Japan, where established government agencies exist to provide careful oversight of the implications of the studies for human subjects. Less desirably, but more probably, it might happen in clandestine fashion in some offshore laboratory where a couple desperate for a child has put their hopes in the hands of a researcher seeking instant renown.

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