According to this theory, the aging process is, at least in part, caused by damage to nuclear DNA, and to the related protein production mechanisms in cells. In actuality, cells do have the capability of repairing nuclear DNA damage of this kind.

However, the Errors and Repairs Theory postulates further that repairs are never quite 100 percent. You might compare these kinds of cellular repairs to repairs done on a car that has been in an accident. Often the superficial damage done to the car is no longer detectable after the repair work is done, but stress tests might very well reveal hidden, unrepaired weaknesses within.

And sometimes the signs of the inadequate repair work are only too detectable, with doors or fenders improperly aligned, etc. Just as imperfect repair work done on a car will almost certainly hasten its aging and curtail its life expectancy, so too, current thought holds, imperfect repair work done on damaged DNA will similarly take its toll.