1. Damage theory

This theory was developed by Denham Harman MD in 1956. The term free radical describes any molecule that has a free electron, and this property makes it react with healthy molecules in a destructive way.

Aging is the result of accumulated errors from excessive free radical damage. Diseases like cancer are the accumulation of structural damage to our cells from being constantly bombarded by metabolically generated free radicals. Oxygen free radicals are thought to greatly increase the severity of, if not cause, such life-shortening diseases as diabetes, strokes, and heart attacks. Since longer-lived species have lower rates of free radical generation than do shorter-lived ones, then life span may be dependent upon our ability to prevent oxidative damage from free radicals.

Look out tomorrow for the second of the current theories on why we age.