William Hurlbut, a physician and ethicist, is best known as a member of the President's Council on Bioethics. Though he has spoken out against the destruction of embryos for research purposes, he is nonetheless a supporter of ­embryonic-stem-cell research. He avoids what would otherwise be a terminal para­dox through a proposal that he calls "altered nuclear transfer," or ANT. His goal: to create embryonic stem cells without destroying human embryos.

One of the most promising methods for creating embryonic stem cells is cloning: the nucleus of an egg cell is replaced by the nucleus of an adult cell, a process called somatic-cell nuclear transfer. The egg is then induced to divide, and the stem cells harvested from the resulting embryo are pluripotent, meaning they can form any sort of tissue in the body. But harvesting the stem cells destroys the embryo. By contrast, ANT (which has been shown to work in mice, if not humans) switches off vital genes--through alteration of the somatic-cell nucleus, the cytoplasm of the egg, or both--before the transfer takes place. Hurlbut says the resulting cell mass could not become an embryo but could produce pluripotent stem cells.