Retesting the commitment theory of cellular aging.

The commitment theory of human fibroblast aging predicts that 55 percent of cells will be nondividing at the middle to late stages of the replicative lifespan; in the present study, however, fewer than 10 percent were nondividing. The fact that no immortal diploid cells have yet been reported is also at odds with the theory. Available data on the variable life-span of clones and mass cultures, the dependence of longevity on population size, and the predominance of certain cell types at termination of a culture are compatible with simpler theories, which support the idea that the limited replicative life-span of diploid fibroblasts is a valid model for organismic aging.