Denham Harman, Aging: A Theory Based on Free Radical and Radiation Chemistry. J. Gerontol. 11, 298-300 (1956).

"Aging and the degenerative diseases associated with it are attributed basically to the deleterious side attacks of free radicals on cell constituents and on the connective tissues. The free radicals probably arise largely through reactions involving molecular oxygen catalyzed in the cell by oxidative enzymes and in the connective tissues by traces of metals such as iron, cobalt, and manganese."

Dr P observes: Notice how Dr Harman (50 years ago!) clearly states both the "Big" and the "Small" models for free radicals and aging. The "Big" model is that free radicals have a direct role in the aging process. the "Small" model is that many of the the degenerative diseases that persons generally die of have an underlying free radical component. The Big model still awaits direct proof. The Small model is generally-accepted.