Creation of the embryos -- grown from cells taken from the company's chief executive and one of its investors -- also offered sobering evidence that few, if any, technical barriers may remain to the creation of cloned babies. That reality could prompt renewed controversy on Capitol Hill, where the debate over human cloning has died down of late.
Five of the new embryos grew in laboratory dishes to the stage that fertility doctors consider ready for transfer to a woman's womb: a degree of development that clones of adult humans have never achieved before.
No one knows whether those embryos were healthy enough to grow into babies. But the study leader, who is also the medical director of a fertility clinic, said they looked robust, even as he emphasized that he has no interest in cloning people.