Advanced Cell Technology Inc., based in Worcester, Massachusetts, created an international furor when it announced it had cloned a human embryo Nov. 25.
The company's chief executive officer, Michael West, stressed his researchers had no intention of creating cloned babies but wanted to use the embryos as sources of valuable stem cells.
But rival scientists pointed out that the ACT team did not even get close to creating embryos large enough to take stem cells from. Only one of the eggs survived as long as the six-celled stage.
British scientists who created Dolly the sheep, the first cloned mammal, called the work very preliminary.
"It is more a political and ethical milestone than it is a scientific milestone, and certainly not a scientific breakthrough," said one researcher.
But most agreed there was a valid reason to do the work. It holds the promise of someday allowing a doctor to create a perfectly matched piece of tissue, or even perhaps a new organ, such as a heart, for transplant.
Poll results published Nov. 26 showed that 53 percent of Americans support cloning research for medical reasons.