At the Salk Institute in La Jolla, Calif., scientists are trying to get time to run backward. In the first attempt to reverse ageing by reprogramming the genome, they have rejuvenated the organs of mice and lengthened their life spans by 30 percent. The technique, which requires genetic engineering, cannot be applied directly to people, but the achievement points toward better understanding of human ageing and the possibility of rejuvenating human tissues by other means.
The Salk team’s discovery, reported in the Thursday issue of the journal Cell, is “novel and exciting,” said Jan Vijg, an expert on ageing at the Albert Einstein College of Medicine in New York.
Leonard Guarente, who studies the biology of ageing at M.I.T., said, “This is huge,” citing the novelty of the finding and the opportunity it creates to slow down, if not reverse, ageing. “It’s a pretty remarkable finding, and if it holds up it could be quite important in the history of ageing research,” Dr. Guarente said.
The finding is based on the heterodox idea that ageing is not irreversible and that an animal’s biological clock can in principle be wound back to a more youthful state. The ageing process is clocklike in the sense that a steady accumulation of changes eventually degrades the efficiency of the body’s cells. In one of the deepest mysteries of biology, the clock’s hands are always set back to zero at conception: However old the parents and their reproductive cells, a fertilised egg is free of all marks of age.

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