Research teams at two prestigious universities announced a major feat of biological alchemy this week: They've taken ordinary human cells and turned them into cells with all the characteristics and promise of embryonic stem cells.

This entirely new way to derive what the researchers are calling induced pluripotent stem (iPS) cells uses neither eggs nor embryos. Instead, it reprograms body cells, reactivating genes that return them to the undifferentiated state characteristic of "conventional" embryonic stem cells.

If the new technique holds up, it will also reprogram the science and politics of stem-cell research.

Consider first the technical advance that so-called "direct reprogramming" represents. It starts with bits of skin - biological materials that are plentiful and readily available, instead of eggs that have to be extracted from women with invasive and risky procedures. Nor does it require embryos, whose destruction evokes strong objections from some religious conservatives.

What's more, direct reprogramming promises to deliver the benefits that cloning-based stem-cell research was thought to offer, without its major risks. It could yield disease-specific stem cells that would be valuable in screening drugs for safety and efficacy, or in studying early disease processes. If researchers can learn to control the differentiation and prevent the tumor-forming tendencies of iPS cells - the same challenges they face with other sorts of embryonic stem cells - then the new method could someday be used to produce patient-specific treatments or replacement tissues that wouldn't trigger immune reactions.

If direct reprogramming fulfills these expectations, it will be difficult to argue for continuing to experiment with cloning techniques that require large numbers of women's eggs and increase the chances of unauthorized efforts to create a cloned human being.

In fact, Ian Wilmut of Dolly-the-cloned-sheep fame reached that very conclusion last week, and announced that he'll no longer participate in what scientists had been calling the "cloning race." Since Wilmut leads one of the handful of cloning research teams in the world, and holds one of only two licenses in the United Kingdom to work on cloning techniques, his decision has practical as well as symbolic meaning.

Of course, many technical hurdles remain before iPS cells are ready for the doctor's office. But the work seems to be moving extraordinarily quickly. There's been little progress in cloning research over the past 10 years. Although primate embryos were finally cloned for the first time earlier this month, it still takes hundreds of eggs to produce a stem-cell line, across all the species that have been cloned. By contrast, researchers were able to transfer their success in direct reprogramming in mice to human cells in less than six months.

In short, the technical prospects of direct reprogramming are overwhelmingly positive. And its political promise is also enormous. It could smooth the contention and polarization that have marked the stem-cell debate, disconnect the stem-cell issue from culture-war battles over embryo politics and abortion rights, and put an end to the use of embryonic-stem-cell research as a political wedge issue. We can even hope to see policy-makers move forward with much-needed oversight of emerging biotechnologies, including a federal ban on human reproductive cloning.

What lessons about politics and science should we take from this turn of events? Some may be tempted to argue that political values should be kept out of decisions about scientific research and new technologies. But that would be a mistake. There's a right way and a wrong way to join politics and science; the stem-cell debate offers a prime example of how not to do it.

Partisan political expediency doesn't belong in science. But we do need thoughtful debate, nuanced decisions, and careful policy-making on human biotechnologies. And we surely want to bring into these considerations our best sense of the technologies' likely social consequences, and our commitments to human rights, social justice and the public interest.

MARCY DARNOVSKY is associate executive director at the Center for Genetics and Society in Oakland. She wrote this article for the Mercury News.