Programmed Aging

What it proposes

Aging is the outcome of an evolved genetic program, with active regulation that produces predictable, sometimes timed, decline. In strong form: aging serves a population-level fitness purpose (turnover of generations enables adaptation).

The traditional objection

Standard evolutionary theory (Williams 1957) held that selection cannot favour a program that harms the individual, because individuals carrying “non-aging” mutations would out-reproduce others. Programmed aging was therefore considered impossible without group-level selection mechanisms, which are usually weak.

Renewed interest

Modern evidence consistent with at least some programmed element:

• Epigenetic clocks tick at a remarkably steady rate within species, suggesting a regulated process.
• Yamanaka reprogramming can rewind epigenetic age in cells — evidence that age is encoded in a program of marks, not just damage.
• Lifespan-determining genes (daf-2, sirtuins, mTOR) tightly regulate aging in many species.
• Pan-mammalian lifespan ranges spanning four orders of magnitude with related anatomies are hard to explain by damage alone.

How to think about it

The current synthesis: aging is part programmed (the regulated component) and part stochastic damage (the accumulated component). Where they meet differs by tissue and species.

Related entries

Antagonistic pleiotropy, Information theory of aging, Epigenetic alterations.