But ethical concerns are not the only argument against cloning. Technical concerns also arise. Mammal cloning appears to have an "efficiency" rate of "approximately 2% of manipulated embryos, a number that seems not to be affected by the species used or the type of cell used as a nuclear donor." The pregnancies of cloned implants can be problematic, and the offspring may suffer from "a wide variety of abnormalities" (Iannaccone A469). In February 2003, for example, Dolly, cloned from adult sheep cells in 1996, was put down, suffering from diseases more typical of animals of more advanced age (Kolata A4). Meanwhile, in 2001, a group of researchers in Worcester, Mass., created what were said to be the first cloned human embryos for stem-cell research, but none of them developed beyond six cells (Johnson 34).

Some opponents of human reproductive cloning cite the "centrality of sexual recombination in mammal reproduction, and argue that it would be extremely difficult to predict either the vi

Kolata, Gina. "First Mammal Clone Dies: Dolly Made Science History. The New York Times 15 February 2003: A4.

Mooney, Chris. "The Future Is Later." The American Prospect 13 (15 July 2002): 10-11.

Advocates of therapeutic cloning argue that stem-cell research, aimed at using cell therapy to strengthen immunity and genetic makeup, should be conducted on embryonic stem cells, which are the most potent kind (Brown 651 passim). Some researchers say "therapeutic cloning ought to be treated differently from cloning to make a baby" (Singer 88). Similarly, Mooney cites the "army of patients suffering from serious and often life-threatening degenerative diseases" (Mooney 10).

Cohen, Jacques, and Tomkin, Giles. "The Science, Fiction, and Reality of Embryo Cloning." Ethical Issues in Human Cloning: Cross-Disciplinary Perspectives. Ed. Michael C. Brannigan. New York: Seven Bridges P, 2001. 11-20.