I hope that all of you will take a look at the free chapter of my new book, The Telomerase Revolution, that has just been posted on Singularity: https://www.singularityweblog.com/why-we-age/#comments. If you find the chapter provocative, please buy the book and read it carefully.
The question of “Why we age” (the title of the chapter excerpted here) is not only a good question, but probably all-but-impossible to answer with any certainty. For one thing, it’s notoriously difficult to do really good, meaningful experiments in answering evolutionary questions. We are stuck using either descriptive cases or experimental models that have short lifespans and arguable relevance to the questions we are asking. Moreover, part of the problem in understanding why we age is that — until recently — we really had no idea what we meant by “age”. There has long been an (often unstated and unexamined) assumption that organisms simply age because of entropy and that specific genes (as opposed to patterns of gene expression) determined aging. Not knowing how aging actually happened naturally led to faulty conclusions about why it happened.
Is my suggestion about “why we age” the correct one? I doubt it, but I suspect that my answer is likely to provide a slightly more realistic start on a reasonable answer because it begins with a more accurate understanding of what we mean by “age”. If we want to explain why infectious diseases evolve over time, then it helps if we know about bacteria, viruses, chlamydial organisms, fungi, and prions. Once we understand what causes infectious disease, we can talk about the evolution of microbial organisms; once we understand what causes aging, we can talk about the evolution of aging.