11. Aging Is Not Programmed

Aging is not a program in the sense of an evolved sequence whose purpose is to cause deterioration (2–5, 18–20). Instead, what is programmed are life processes, such as development, reproduction, and maintenance, whose imperfect execution produces the deleteriome. Aging only has the appearance of a programmed process (i.e., it is programmatic or quasi-programmed), as it proceeds according to, and as a consequence of, ongoing biological programs. Evolution can shape the rate and pattern of aging by selecting for more effective defenses against damage (or by relaxing selection when early reproduction is favored), but the default direction remains, as in the face of imperfect maintenance, deleterious changes accumulate. This view is compatible with classic evolutionary reasoning about declining selection with age, while keeping the causal arrow on the imperfect execution of biological processes and intrinsic limits on maintenance. It also accounts for rapid deterioration associated with reproduction, as in Pacific salmon. Natural selection acts on specific functions, survival, reproduction, growth, repair, and behavior, many of which influence aging indirectly (21).