But Ian Wilmut, who created Dolly the sheep, says Advanced Cell's work on cows is encouraging.

FORBES: Dolly The Sheep Dies

Dr Ian Wilmut, who created Dolly, the world's first cloned sheep, said it took 277 tries to get it right.

CNN: Team to attempt human cloning

Professor Ian Wilmut is to receive a knighthood for his pioneering work at the Roslin Institute near Edinburgh - including cloning the first mammal.

BBC: Dolly creator heads Scots honours

The Roslin Institute's Dr. Ian Wilmut, who pioneered the technique that cloned Dolly from a single mammary cell from an adult sheep, said that while human cloning is theoretically possible, he saw no reason to do so.

CNN: Oppose experiments on humans