“We don’t have any idea why we age, or actually we have lots of ideas; we just don’t know if any of them are correct. Almost thirty years ago, Zhores Medvedev, a Russian biogerontologist, counted some three hundred serious scientific theories to explain why we age, and the number has not shrunk in the decades since. As Professor José Viña and colleagues from the University of Valencia put it in a summary of current thinking, the theories fall into three broad categories: the genetic mutation theories (your genes malfunction and kill you), the wear-and-tear theories (the body just wears out), and the cellular waste accumulation theories (your cells clog up with toxic by-products). It may be that all three factors work together, or it may be that any two of the above are side effects of the third. Or it may be something else altogether. No one knows. Bryson, Bill. The Body (p. 370). Knopf Doubleday Publishing Group. Kindle Edition. ”
