A paper by Aubrey de Grey outlines his view of nuclear DNA damage and aging: "Since Szilard's seminal 1959 article, the role of accumulating nuclear DNA (nDNA) damage - whether as mutations, i.e. changes to sequence, or as epimutations, i.e. adventitious but persistent alterations to methylation and other decorations of nDNA and histones - has been widely touted as likely to contribute substantially to the aging process throughout the animal kingdom. Such damage certainly accumulates with age and is central to one of the most prevalent age-related causes of death in mammals, namely cancer. However, its role in contributing to the rates of other aspects of aging is less clear. Here I argue that, in animals prone to cancer, evolutionary pressure to postpone cancer will drive the fidelity of nDNA maintenance and repair to a level greatly exceeding that needed to prevent nDNA damage from reaching levels during a normal lifetime that are pathogenic other than via cancer or, possibly, apoptosis resistance." In other words, beyond sufficient work to prevent cancer, we don't need to repair nuclear DNA over a human lifetime. Maybe. This debate is ongoing; there are many others who argue that DNA damage is an important root cause of aging.

Link: http://www.ncbi.nlm.nih.gov/pubmed/17588643