Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Aging and the geroscience hypothesis, published by DirectedEvolution on July 12, 2023 on LessWrong.

Cautionary introduction

I am a biomedical engineer with an interest in the science of aging. The Handbook of the Biology of Aging, 9th ed, is a great 400-page introductory resource, looking at aging on every level from evolutionary and conceptual, to public health, to specific molecular and organ systems, to genetics, to immortal organisms.

My goal is to teach readers key concepts and facts about aging research in short posts with accessible language. I follow the substance of the handbook chapters, though I sometimes reorganize them. I'm also presenting the chapters out of order, because I think it creates a better narrative. I encourage readers to take the facts and concepts tentatively - they are just pointers to a rich and sometimes controversial underpinning literature. My hope is that some readers will go on to read the handbook and explore the literature it cites.

Chapters will be presented out of order in order to improve the overall narrative flow. This post is for chapter 4:

Hornsby, P. J. (2021). The nature of aging and the geroscience hypothesis. In Handbook of the Biology of Aging (pp. 69-76). Academic Press.

Next: Compression of morbidity (available 7/12/2023)

The nature of aging and the geroscience hypothesis

This chapter is about making sense of a seemingly paradoxical thesis:

The fact that aging and injury are inevitable should encourage us about the possibility of advanced medicine that makes frailty and death preventable.

Your body is made of physical stuff - DNA, proteins, sugars, fats, cells, tissues, and organs - and physical stuff, left alone, inevitably breaks down and becomes disordered. The longer you live, the more chances you take with car crashes, disease, and other external causes of death. Aging is entropy - the inevitable process by which the laws of physics guarantee that a system will become disordered over time.

Yet the entropy of aging and injury is something we fight every time we heal a wound (or for that matter, repair a car or clean the house). Physics also tells us that we can repair the damage of aging and injury as long as we have the skill and energy to do so.

The fact that physics guarantees we'll experience aging and injury means we can reject the idea that aging is somehow directly beneficial to us or to our species. By Occam's Razor, there's no need to suppose some evolutionary benefit from aging and injury, since they're already explained perfectly well by entropy.

Yet as we'll see, not all evolutionary pressures tend in the direction of longer, healthier lives, so we can't expect that evolution has already taken every opportunity to preserve our health for as long as possible.

Together, these facts are encouraging. They mean that we can reject the pessimistic notions that evolution has already endowed us with the longest, healthiest lives possible, or that frailty and death are the inevitable results of entropy. Therefore, modern medicine has plenty of scope to add new maintenance and repair abilities to those our bodies already possess.

Point #1: There is no need to speculate that evolution is making you age "on purpose" or that it's already endowed us with the longest, healthiest lives possible.

Of course, you can die from a disease, predator, car accident or gunshot wound, not only by aging. Aging can make you more vulnerable. But there's a meaningful difference between being eaten by a shark, succumbing to pneumonia after years of declining health, and dying peacefully in your sleep at age 102.

Point #2: There's a difference between aging and extrinsic causes of death, but they interact.

We can overcome the extrinsic damage and gradual aging of our houses, cars and clothing with cleaning, maintenance and repair. The...