SHUN CLONING : Scientists must speak out.

Scientists say evidence is mounting "that creating healthy animals through cloning is more difficult than they had expected." So began a front-page story in the New York Times (March 25), highlighting the frustrations of animal cloners, and the chance that human cloning may prove technically impossible. Those worried about the ethics of human cloning have greeted this as good news, a sign that the slippery slope is leveling out. Unfortunately, the new obstacles may prove less than insurmountable in the long run--and in biotechnology, the long run often proves surprisingly short. For those whose doubts about biotechnology are expressed by the philosopher Leon Kass as "the wisdom of repugnance," it is no time to relax: The slope may soon steepen once more.

In cloning, a cellular nucleus from the adult to be cloned is injected into an egg from which the nucleus has been removed. As it turns out, the environment of the unfertilized egg, hijacked for cloning purposes, is able to "reprogram" adult nuclei, returning their DNA to a naive, pseudo-embryonic state. As the egg develops, it follows the genetic blueprint of the adult from which the nucleus was derived, essentially producing an identical twin of that individual. But there are problems. When Ian Wilmut and his co-workers produced the cloned sheep Dolly, they caught most biologists unawares because it was thought impossible to clone a mammal. Frogs had been cloned more than twenty-five years ago, but many biologists thought that a phenomenon termed "imprinting" would prevent mammalian cloning. Imprinting confers "memory" on a developing cell, helping to distinguish adult skin cells, for instance, from heart, liver, and blood cells. Experiments in mice suggested that imprinting permanently altered the DNA, making it impossible to derive a viable embryo from an adult nucleus. Dolly changed all that. Still, the cloning of mammals is a precarious enterprise. Wilmut himself acknowledged that cloning was inefficient and fraught with grotesque failure, and he strongly advised against trying to clone humans. Even the most experienced researchers are able to generate viable clones only 2 to 5 percent of the time. The failures appear to stem from the imprinting phenomenon, which had been discounted post-Dolly: the genetic absolution conferred by the egg turns out to be inefficient at best, and adult memories persist in the DNA of cloned embryos, interfering with their development.

This point was made by MIT developmental biologist Rudolf Jaenisch during testimony before a House subcommittee on March 28, and in a forceful article he co-authored with Wilmut, "Don't Clone Humans!" (Science, March 28). As Jaenisch and others stressed before Congress, the high failure rate in animal cloning should make human cloning unthinkable. The proponents of cloning, a motley crew of UFO cultists and fringe physicians, argue that they will succeed in humans where experts have failed in animals. Their position is, of course, untenable. For now, human cloning will probably end up prohibited. However, there is a danger in arguing against cloning on technical grounds alone: Once the procedure is perfected, it implicitly becomes ethically permissible.

For the time being, human cloning remains a fantasy, well outside the scientific mainstream. Nonetheless, few biologists or physicians have spoken out against it as a matter of principle, and professional groups have called for little more than a moratorium on efforts to clone a human being. Now is the time for cloning opponents to reach out to the research community and engage it in a conversation that is grounded in social ethics rather than technique. At the moment, scientists are insulated from such considerations. The congressional hearings of March 28 were neatly divided into a "science" portion, in which Jaenisch spoke, and an "ethics" portion that featured the testimony of cloning advocates and of bioethicists, the presumed conscience of the scientific community. The bioethicists' qualifications in this regard are marred by their lack of consensus; the testimony before the subcommittee ranged from Arthur Caplan, who forthrightly called for a ban on cloning in the name of individual dignity, to Gregory Pence, who objected to the term "clone" as a pejorative, analogous to "chick" (he offered "delayed twin" as a more palatable alternative). In any event, as Gordon Marino has pointed out in these pages ("Avoiding Moral Choices," March 23), the existence of a class of ethics experts does not relieve scientists, or anyone else, of the burden of moral responsibility.

Many practices already skulk at the margins of society that would deform our social space if they became the norm; "swinging," for example, or hallucinogenic drug use. Should the day of the clones arrive, our best hope of preventing the practice from becoming widespread is to persuade mainstream scientists and physicians to shun it. I am hopeful that the scientific and medical communities will respond to these dangers first as sons, daughters, and parents, realizing that their relationships are as threatened as anyone's by the prospect of a brave new cloning world. In fact, in their Science article, Jaenisch and Wilmut prefaced their warning about the technical dangers of cloning with the acknowledgment that "there are many social and ethical reasons why we would never be in favor of copying a person." Arresting our descent on the slippery slope will require that scientists themselves elaborate on those reasons.

Charles Murtaugh is a research fellow in the Molecular and Cellular Biology Department at Harvard University.