"Since 1998, when a University of Wisconsin team first isolated embryonic stem cells grown from a human embryo, researchers have sought to use cloning techniques to create such cells that would be genetic copies of ones belonging to sick patients. The same cloning techniques, which essentially place a new set of genes into a hollowed-out egg, and then kick-start the combination to start dividing and become an embryo, have been used since the cloning of "Dolly the Sheep" in 1996. That helped to create genetic copies, twins, of animals ranging from prize bulls to an extinct kind of wild goat. In those cases, the embryos were implanted into a surrogate mother instead of being destroyed to harvest stem cells. Knoepfler warned that fertility clinic operators outside the USA might try to replicate the team's method to try to clone a human baby. However, Mitalipov says that his team's technique would not likely create a cloned embryo that could be implanted into a surrogate mother's womb and lead to a pregnancy. "The embryos we produce this way did not lead to pregnancy in monkeys," he says. "We think there is something in the manipulations to make them that make a successful pregnancy impossible.""