Daisy, Diana, Debbie, and Denise, four sheep cloned from the same cell line as the world-famous Dolly are challenging the notion that cloning causes premature aging, The New York Times reports. That’s because, along with nine of their younger sisters, the sheep appear to be aging normally after passing the ripe old age of 7. Daisy, Diana, Debbie, and Denise are now 9, or about 70 in human years. Scientists reached their conclusion after testing for osteoarthritis, type 2 diabetes, and heart disease, all markers of the aging process. The researchers hope that their findings will lead to a revitalization of research involving cloned animals.