Ignore the noisy debate around cloning, Rudolf Jaenisch quietly insists, and instead look closely at the biology involved. First, note that there are two different kinds of cloning: reproductive cloning, the attempt to create an exact replica of a human being, which Jaenisch believes to be both biologically flawed and morally questionable; and therapeutic cloning, which offers potential cures to some of mankind’s most devastating diseases, and from Jaenisch’s point of view, sidesteps ethical pitfalls. Both involve transferring the genetic material from a somatic cell (from the skin, for instance) into an individual egg cell. The fertilized cell gives rise to embryonic stem cells, which have the near miraculous capacity to differentiate into every kind of tissue found in the body. Jaenisch says human embryonic stem cell research could help reveal the mechanisms behind biological growth, and enable a customized approach to treating such diseases as diabetes and Parkinson’s. Once scientists create these ES cells, they can grow them in vitro.

Ethical problems emerge, Jaenisch believes, when a cloned embryo is implanted in a uterus with the intent of creating a full-term clone, or with the intent of harvesting stem cells from an aborted fetus. These involve the “destruction of potential life.” The creation of cloned ES cells for research purposes, however, is the “propagation of existing life,” says Jaenisch.

Stephen Marks delineates the various human rights arguments around cloning: Are we at risk “of turning people into products?” Can “we pursue genetic health and enhancements” while maintaining the individual’s dignity? He describes the U.S. administration’s current opposition to any form of cloning and in particular, its attempt to throttle international treaties that might eventually permit therapeutic cloning.