physics makes aging inevitable, not biology?

nautilus |  Four years ago, I published a book called Life’s Ratchet, which explains how molecular machines create order in our cells. My main concern was how life avoids a descent into chaos. To my great surprise, soon after the book was published, I was contacted by researchers who study biological aging. At first I couldn’t see the connection. I knew nothing about aging except for what I had learned from being forced to observe the process in my own body.

Then it dawned on me that by emphasizing the role of thermal chaos in animating molecular machines, I encouraged aging researchers to think more about it as a driver of aging. Thermal motion may seem beneficial in the short run, animating our molecular machines, but could it be detrimental in the long run? After all, in the absence of external energy input, random thermal motion tends to destroy order.

This tendency is codified in the second law of thermodynamics, which dictates that everything ages and decays: Buildings and roads crumble; ships and rails rust; mountains wash into the sea. Lifeless structures are helpless against the ravages of thermal motion. But life is different: Protein machines constantly heal and renew their cells.

In this sense, life pits biology against physics in mortal combat. So why do living things die? Is aging the ultimate triumph of physics over biology? Or is aging part of biology itself?