In an advance online publication on February 2, 2006 in the journal Science, biologists from Brown University reported a connection between the age of baboons and the number of aging cells in their skin, boosting the theory that cellular senescence is associated with an aged body. Replicative senescence occurs when cells lose their ability to divide after a number of replications. Senescent cells are associated with skin wrinkles, weakened immune response and other age related conditions and diseases.

Professor of medical science John Sedivy and colleagues examined skin samples from the forearms of 30 baboons aged 5 to 30 for biomarkers of cellular aging. They found an exponential increase in DNA double-strand breakage with the animals' increasing age, reaching 30-35 percent in the oldest animals. The most important biomarker, telomere dysfunction-induced foci (TIF) which show that telomeres have shrunk to the extent that cell division is halted, were found in 4 percent of the tissue cells of 5 year old baboons and in up to 20 percent of the cells of the 30 year olds.

The authors observed that telomeric DNA damage may not be entirely due to replicative exhaustion, and note that oxidative stress increases the rate of telomere shrinkage.

Dr Sedivy commented, "For 40 years, we've known about replicative senescence. Whether it promotes the aging of our bodies, however, is highly controversial. While it may make intuitive sense, skeptics say 'Show us the evidence.' The first solid evidence is in this study. These initial findings won't settle the debate, but they make a strong case."

"There is good evidence that senescent cells are not benign," he added. "But until now, no one has been able to confirm that they exist in appreciable numbers in old animals."