UK scientists caused quite a stir two decades ago when they announced the world's first clone of a mammal, Dolly the Sheep.  That experiment famously didn't end so well, but now they say Dolly has four little sisters who are doing well.

"Daisy, Debbie, Denise and Diana," says David Sinclair, a developmental biologist at the University of Nottingham.  "'Sister clones' probably best describes them," he explained, "They actually come from the exactly the same batch of cells that Dolly came from."

A stunned world greeted news of Dolly with wonderment and trepidation, not knowing what effect this would have on agriculture or food production, not to mention Alice Cooper songs or the creation of armies for the Galactic Empire.  But Dolly didn't last that long.  She died after only seven and a half years of a lung infection that was unrelated to her clone status.

But she also suffered premature osteoarthritis, and the tips of her chromosomes were short - suggesting that the cloned sheep aged more quickly than a normal sheep.

This week, we learned that the University of Nottingham has 13 cloned sheep, including the four genetic equivalents of Dolly.. And:  "There is nothing to suggest that these animals were anything other than perfectly normal," says Sinclair.  The girls are nine years old, which is equal to about 70 in people years.  Debbie has arthritis, but it isn't too bad - her movement is indistinguishable from 'normal' sheep.  And that's reigniting interest in the cloning process that created Dolly and her sisters, called somatic-cell nuclear transfer.  

"It provides another boost to those of us who are hoping this technology might someday be useful for conservation," says Beth Shapiro, an evolutionary biologist at the University of California, Santa Cruz.  She's the author of the book "How to Clone a Mammoth: The Science of De-Extinction".

But instead of going to work for John Hammond and InGen on Isla Nublar off the coast of Central America, Dr. Shapiro is one of the scientists interested in using the technology to rescue critically endangered species from extinction, or re-balancing an eco-system if a loss of a species would cause a ripple effect.

"This science is showing us (that) if we can get by what we know is the trickiest and least efficient part of this process, then the clones that are born are, in essence, just like anything else that's alive - perfectly healthy and perfectly capable of living to old age," she said.