Dolly the world’s first cloned mammal has been put to sleep. At an age of six (when sheep are known to live 11 or 12 years), she was diagnosed with Progressive Lung Disease. (A disease common in older sheep who live inside, but 6 isn’t considered old.) Last year, it was reported Dolly had contracted arthritis, and there was much speculation that current methods of cloning cause premature aging. It appears there is now more evidence for this theory.