Aging is a biological process that results in progressive functional decline and increased vulnerability to disease. Death due to aging is considered to be “natural”. However, aging does not have to be an inevitable consequence of the passage of time. In general terms, aging can be thought of as biological damage that occurs at a rate that outstrips the body’s ability to repair it. There are many theories as to exactly why we age, although none have been definitively proven. However, it is unlikely that any single mechanism is wholly responsible for the aging process.