Sheep Dolly, 6, Dies; Pioneer Clone’s Birth Sparked Debate

Dolly, the world’s first cloned animal, has been euthanized because she was suffering from a progressive lung disease common in much older sheep, her creators said Friday.

Dolly’s short life -- she was born July 5, 1996 -- was a pioneering one. Her creators, a team of embryologists at Scotland’s Roslin Institute headed by Ian Wilmut, defied scientists who believed that cloning from adult cells was biologically impossible.

Her birth, they said in a statement Friday, “revolutionized the way we think about animal development.”

The birth of Dolly also gave rise to a furious debate on the ethics of cloning. More animals have been cloned throughout the world since Dolly was born, and the British government has now authorized cloning of embryos for research into human diseases.

The initial diagnosis of the cause of Dolly’s death was a lung disease “common in older sheep, particularly those housed inside,” said Harry Griffin, one of her co-creators at the institute. He added that a full post-mortem will be conducted and any significant findings reported.

Dolly was cloned from adult sheep cells and gave birth to six healthy lambs in her lifetime, as well as some that did not survive, all normal biological events in the life of a normally conceived sheep.

But in January 2002, she developed arthritis, giving rise to concerns that cloned animals could be prone to premature aging. Dolly was cloned from a 6-year-old sheep, which could arguably put her age at death at 12 rather than 6. The normal life expectancy of a sheep is 12 years.

“It is not possible to know if her condition is in any way a result of her being a clone,” Wilmut said when her arthritis was diagnosed.

Cloning -- creating a genetic replica of another creature -- is achieved by removing the genetic material from an egg and replacing it with genetic material from a nonreproductive cell. In addition to sheep, scientists have also cloned mice, cows, goats, pigs, rabbits and a cat.

Other species -- such as dogs and rhesus monkeys -- have proven more difficult and have not yet been cloned.

An eccentric group known as the Raelians recently claimed that it has cloned several human babies but has provided no evidence to support this claim. It has been widely dismissed by scientists.

Even in species in which cloning has been achieved, the failure rate is high, and many animals die before birth or shortly afterward. Those that survive can develop health problems such as obesity. Scientists think that such problems occur in clones because of mistakes in the regulation of genes, leading to errors during development.

Gerald Schatten, professor and vice chair of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh, said that it is possible that even normal-seeming clones may have problems that only emerge later in life. However, he said, it is not possible to conclude that Dolly’s arthritis and lung problems had anything to do with her origins. One would have to study many more animals to make that kind of link.

Dolly had a very unnatural life for a sheep, Schatten noted. For instance, because she was a celebrity animal, she lived in a special barn instead of the outdoors, perhaps rendering her more prone to lung maladies.

She also learned to stand on her hind legs and beg for treats, which might have caused her arthritis and obesity.

“She got incredible attention,” Schatten said. “And as a result of that incredible attention, she got a little weird.”

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Stobart reported from London and Mestel from Los Angeles.