One of the oldest and best-established theories of aging holds that we age because of oxidative damage. In the classic version, the body exploits high-energy chemistry based on oxidation for an energy supply at the cellular level, but this involves constant exposure to these high-energy species and the free radicals that are their by-products, species which can attack sensitive biomolecules. Damage to these molecules accumulates over a lifetime, so the story goes, and makes the body gradually less able to maintain its balance. I’ve argued against the general idea that aging is an accumulation of damage, because of evidence that it is an active process, closely regulated like everything else about life. But new to me this week is a version of the theory by Spanish physiologist Gustavo Barja, in which some of the same chemistry is described as an active program of self-destruction. Barja argues that the process of burning fuel to produce energy can be extremely clean or it can be rather dirty. It is the “leakage” of free radicals during the process that causes the damage of aging, and this leakage can be quite fast, or it can be almost nil. Leakage is tightly-regulated in a way that determines life span. This is a unique lens through which to view aging. What does it help us to understand?