Cloning extends life of cells—and cows?

Last year, the scientists who created Dolly the cloned sheep raised the concern that she was aging prematurely. Their fear was prompted by the finding that protective tips on her chromosomes seemed shorter than normal for a lamb her age. A new study of cloned cows counters that disquieting finding, however. It even suggests that cloning can create cells, and perhaps animals, that thrive longer than normal.