Cracking the Aging Code: The New Science of Growing Old-and What It Means for Staying Young
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Cracking the Aging Code: The New Science of Growing Old-and What It Means for Staying Young
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Overview
A revolutionary examination of why we age, what it means for our health, and how we just might be able to fight it.
In Cracking the Aging Code, theoretical biologist Josh Mitteldorf and award-winning writer and ecological philosopher Dorion Sagan reveal that evolution and aging are even more complex and breathtaking than we originally thought. Using meticulous multidisciplinary science, as well as reviewing the history of our understanding about evolution, this book makes the case that aging is not something that “just happens,” nor is it the result of wear and tear or a genetic inevitability. Rather, aging has a fascinating evolutionary purpose: to stabilize populations and ecosystems, which are ever-threatened by cyclic swings that can lead to extinction.
When a population grows too fast it can put itself at risk of a wholesale wipeout. Aging has evolved to help us adjust our growth in a sustainable fashion as well as prevent an ecological crisis from starvation, predation, pollution, or infection.
This dynamic new understanding of aging is provocative, entertaining, and pioneering, and will challenge the way we understand aging, death, and just what makes us human.
Product Details
| ISBN-13: | 9781250061720 |
|---|---|
| Publisher: | Flatiron Books |
| Publication date: | 06/14/2016 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 338 |
| File size: | 986 KB |
About the Author
Theoretical-biologist Josh Mitteldorf has a PhD from UPenn. He runs the website AgingAdvice.org, and writes a weekly column for ScienceBlog.com. Mitteldorf has had visiting research and teaching positions at various universities including MIT, Harvard, and Berkeley.
Dorion Sagan is a celebrated writer, ecological philosopher and theorist. His essays, articles, and book reviews have appeared in Natural History, Smithsonian, Wired, New Scientist, and The New York Times, among others.
Read an Excerpt
Cracking the Aging Code
The New Science of Growing Old - and What it Means for Staying Young
By Josh Mitteldorf, Dorion Sagan
Flatiron Books
Copyright © 2016 Josh Mitteldorf and Dorion SaganAll rights reserved.
ISBN: 978-1-250-06172-0
CHAPTER 1
You Are Not a Car: Your Body Does Not "Wear Out"
Just as the constant increase of entropy is the basic law of the universe, so it is the basic law of life to be ever more highly structured and to struggle against entropy.
— Václav Havel
I'm an extraordinary machine.
— Fiona Apple
Doesn't it seem strange that our bodies build themselves miraculously from single egg cells to fully formed, perfectly functioning adults — but then they can't seem to maintain themselves in good repair, as they gradually deteriorate and ultimately fail? It's as if the teen next door, who pieced together a complete 2002 Toyota Camry out of scrap from a junkyard, ran the car into a pothole and couldn't figure out how to change a tire.
Surely it is not a question of can't but won't. The body knows perfectly well how to repair and maintain itself, but that is not part of its genetic program, not part of its evolutionary mission. Modes of repair are shut down progressively as we age.
How Do You Think About Aging As We Begin?
Before I speak to people about aging, I always ask what ideas they have come to on their own. Everyone has thought about aging, at least enough to come to terms with it in their loved ones and their own lives. What is aging, and where does it come from?
When I am speaking to an audience of evolutionary biologists, the majority answer that "aging is a pleiotropic side effect of genes for fertility." This is what we referred to as "answer number two" to the mystery of aging in the preface. But outside university evolution departments, I have never found people to respond in this way. Instead, there are two popular notions about aging. About half the educated public already has the right idea (as I shall argue) about the significance of aging; this chapter is addressed to the other half.
The right idea is that aging has been programmed into our genes by evolution, an adaptation to make room in the niche for the next generation to grow up. The effect is to democratize, to keep the community diverse and resilient, and above all to stabilize the ecosystem against lopsided growth of any one species. The wrong idea is that bodies wear out for the same reason that machines do — gradually rusting, accumulating little nicks and dents. If that is the way you think about aging, my goal in this chapter is to convince you otherwise.
Things wear out. Nothing lasts forever. This is the oldest and still the most pervasive idea about what aging is. It is seductive because some aspects of aging fit with this picture; but the idea is also deeply flawed. It is a misapplication of basic physical law, and it also fails to account for some familiar facts about aging.
Bodies Versus Machines
The joints and bearings in your car become pitted and rusted over time, and they continue to work, but with less freedom and more squeaking. Isn't that just what happens to our arthritic knees and shoulders as cartilage wears away? Knives get dull, and the blades develop nicks and chips — just like our teeth. The plumbing pipes in your house become corroded over many decades, and deposits build up on the interior walls, impeding the flow. This sounds a lot like atherosclerosis — coronary heart disease. Often the performance of an older automobile engine suffers because the piston rings wear away, leaking exhaust within the cylinders. Our athletic performance declines with age, and it is natural to imagine it is for similar reasons. Biochemists might speak of "leaks in the electron transport chain" of our mitochondria, which are mini power plants inside each cell. In snowy, salty winters of the American Northeast, car chassis rust out over the years; as New Englanders might say, "The car has cancer." Even computers that have no moving parts are subject to performance degradation with age, because more and more apps are running in the background, each grabbing a chunk of the processor's "attention." Our immune systems fail in a similar mode, as our bloodstream accumulates memory T cells, white blood corpuscles that are expert at responding to diseases from our past, but there is a shortage meanwhile of naïve T cells that can respond to the next challenge.
Most compelling of all are the big problems that appear suddenly and send your car into the shop. The transmission fails, or the brakes wear out, or a rusting exhaust line finally leaks through into the passenger compartment. These problems are much more frequent in an old car than in a new car, and they are the reason that we retire the old car and buy a new one. Our bodies, similarly, become more vulnerable with age. Your chances of suffering a heart attack are fifteen times higher at age eighty than at age forty. You are twenty times more likely to be diagnosed with cancer at age eighty, compared to forty (and ten times more likely to die of cancer). Incidence of ordinary infectious diseases also rises with age, and though the increase is not so dramatic, the same diseases can be far more serious in an elderly person. Taken together, pneumonia and influenza are the eighth leading cause of death in the United States, and almost all these deaths are in people over seventy, most over eighty.
These surface similarities mask some major differences. If you leave your car in the garage most of the time and drive only two thousand miles a year, it will last a lot longer. But if you stay at home and don't use your muscles, you are risking rapid aging and early death. Exercise is the best thing you can do to extend your life. Why doesn't exercise wear your body out the way fast driving wears out a car?
This is our first clue that there is something very different about aging in a living body compared to wear in a machine. The body can fix itself in a way that the machine cannot. So for the body, its state of repair depends on the difference between the damage that is done in living and the repair that is accomplished internally, automatically, by grace of complex evolved physiology.
Better Than New
You might imagine that the body is always doing its best to repair itself, subject to some limits imposed by an energy budget. If the injuries and the damage are at a manageable level, then the body's automatic repair service will keep up, but if you are hard on your body, the repair falls behind, and damage accumulates. That would be a reasonable expectation, but think about it — that's not at all the way your body actually behaves. If you sit all day, get no exercise at all, nothing that would stress the bones or tear the muscles, then the muscles will atrophy, and the bones will soften. On the other hand, if you run or jump or lift weights, then the bones develop microscopic cracks, and the muscles will have tiny tears. Yet the body responds to these stressors by coming back stronger: in this case by building new bone mass, strengthening the muscles.
The more you work your body, the more the repair mechanisms are ramped up. That's not surprising — it's just what you would expect if evolution acted as a systems engineer might, allocating resources where they can do the most good. But the strange thing is that the body overcompensates. The body that works hard stays in very good repair and lasts longest. The couch-potato body is not stressed at all, yet it suffers rapid damage and dies young.
This is not the way a systems engineer would design our mortal coils. A rational designer would budget more resources for repair when the body is working out and needs it more, but it would not neglect the body and let it go to pot when repair is easy. The paradox is that just when resources (i.e., food) are most available and the need for repair (from exercise) is minimal, the body does a lousy job of repair, inviting early death.
Food energy is the currency of the body, the raw material with which the body must maintain itself, compete in the struggle for existence, and reproduce. A well-accepted theory of aging (the Disposable Soma Theory described in chapter 4) is based on the assumption that animal bodies rationally allocate the limited resource of foods. If strapped for resources, your body would be expected to address the most immediate priorities first and skimp on the long-term investment. The immediate priority is survival and reproduction; the long-term investment is the healing that keeps the body in good repair. The theory states, quite reasonably, that the body ought to do the best job of repair when there is plenty of food and when other demands for that food are smallest. So the Disposable Soma Theory predicts that we ought to live long when we eat a lot, exercise very little, and have no children. Women ought to live much shorter lives than men, because they invest so much more energy in reproduction than men do.
The truth is the opposite on all counts. Women have longer life expectancies than men. (In most animal species, too, the females outlive the males.) And women who have more children have a slightly longer life expectancy. The more you exercise, the longer you live. And food deprivation is a royal road to a long and healthy life.
* * *
The best-studied, most reliable laboratory manipulation for extending an animal's life is to feed it less. The less an animal eats, the longer it lives (on average). Animals that are completely emaciated, on the brink of starvation, live longest of all. Mice that are starving and running (miles per day!) on their tread wheels live even longer than the starved mice that don't exercise.
Why should life be cut short when food energy is most plentiful and competing demands for that energy are least severe? We must confront the puzzle that the body is not doing its best to live as long as possible under these circumstances. Damage is accumulating most when it is least necessary. In this sense, aging seems gratuitous, if not perverse.
Plants and Animals That Don't Age
It's a curious fact that some animals (and many plants) don't age at all in the technical sense that they become more likely to die as they grow older. This is another set of facts that doesn't fit with the idea that aging is an inevitable result of wear and tear. There are clams and lobsters that just grow bigger every year, without any of the body part failures associated with old age. There are groves of aspen trees cloned from a single root that are more than ten thousand years old. There are salmon and octopuses and seventeen-year cicadas that have extended periods of development in which they suffer no aging at all; but once they reproduce, they then age and die in a hurry. Looking closely, we'll see that it is not the stress of reproduction that kills them but rather self-destruction that is built into their life plans — a kind of planned obsolescence. Strangest of all are the animals that are able to undo their development, aging backward to an earlier stage in their life cycle, recapturing their youth, and beginning afresh in life.
When to Reppair Your Old Car, and When to Retire It for a New Model
It makes sense to do the small repairs but to trade the car in if repairs are major. You routinely replace the battery and the tires, but if your engine needs an overhaul, it may be more economical to buy a new car than to invest in the old one. Should we expect that Mother Nature treats living bodies in the same way — making small repairs, but starting over from an egg rather than repair major damage in an aging individual?
In the case of cars, the reason for the economic choice-point is that new cars are artificially cheap ("loss leaders," manufactured with underpaid Asian labor), while car parts are artificially expensive (they know at that point that they have no competition). Furthermore, the labor charge to take a car apart, bolt by bolt, and replace a gasket in the heart of the engine is formidable. Bodies don't have this problem, because the repair is performed on-site, cell by cell, without having to disassemble or reassemble anything.
From nature's perspective, it should never be cheaper to throw out an old body and start over from a sperm and an egg. The resources needed for growth of an embryo are enormous, and the failure rate (from egg to adult) is very high. The economics of a body are very different from the economics of an automobile. Why should evolution discard her tried-and-proven winners in favor of a Hail Mary pass to a tiny, defenseless newborn?
Passive Versus Active: Wearing Out Versus Self-Destruction
In fact, if the body looks as though it is wearing out with age, that is because some of the ways in which we age really are passive. The repair functions that were quite adequate in youth slow down with age, and damage is permitted to accumulate. Some aspects of aging seem to work in this way, while others look more like active self-destruction — the body is actually attacking itself.
One example of passive damage is the skin. Skin cells become damaged all the time, mostly with exposure to the sun. In youth, we have skin stem cells that generate fresh, new skin at a pace that can keep up; while in older people, there are fewer stem cells, and the stem cells we have are not working as hard.
An example of active self-destruction is inflammation, which has been found to be at the core of all the Big Three diseases of old age: cancer, heart disease, and Alzheimer's dementia. A second mode of self-destruction is cell suicide, called apoptosis. Apoptosis can be an important function for life, as when a cell becomes infected with a virus and it falls on its sword, dissolving in a cascade of enzymes rather than allowing the virus to take over its reproductive machinery and risk infecting other cells in the body. But apoptosis is also enlisted as a program of death. In later life, some healthy and functional cells are eliminating themselves. This is what causes the wasting in our muscles (sarcopenia) and frailty that we suffer late in life.
I mentioned arthritis above as an example assumed to be simple wear and tear. Until a few years ago, doctors described two kinds of arthritis: rheumatoid arthritis, an autoimmune disease caused by inflammatory attack on the joints; and osteoarthritis, which is simply a loss of cartilage with age. In recent years, the line between the two has blurred.
Osteoarthritis is not wearing out but inflammation. An important defense mechanism apparently has been co-opted for the task of self-destruction. So after all, the reason our knees get creaky isn't like the reason that bearings wear out in a car.
Entropy and All That Jazz
"That's all well and good in practice. But will it work in theory?"
I hope I've convinced you by now that bodies are different from machines, that they don't have to fall apart as they get older, because they can repair themselves; that indeed everyone gets stronger, not weaker, during the time they are growing up.
But what about the theory? Isn't there a physical principle that says everything must deteriorate over time? You may be aware there is a law of nature that rules out perpetual motion machines. This is the law of entropy, which physicists call the Second Law of Thermodynamics. Living things are subject to the laws of physics, like all other matter. So what's up with growth and development that seem to defy the Second Law? And how does the capacity for self-repair fit into the Second Law?
Living and nonliving things both generate entropy. The way in which living things are different is that they don't accumulate entropy in their own bodies, but dump it out into the environment with their waste. Living things can take in energy, which they use to build and to repair their bodies. The Second Law of Thermodynamics applies to sealed, isolated systems, but living things are open systems. This all became clear to scientists during the nineteenth century, when the laws of thermodynamics were first formulated.
Who knew that the idea of "wearing out" could be associated with a precise, measurable physical quantity? This was the brainstorm of Rudolf Clausius (1850). Along with it came the partition of energy into the useful and the useless. The theory was formulated with the example of the heat engine always in mind, as steam was transforming transportation and industry all through Europe. Useful energy is called "free energy," and useless energy is called "entropy."
(Continues...)
Excerpted from Cracking the Aging Code by Josh Mitteldorf, Dorion Sagan. Copyright © 2016 Josh Mitteldorf and Dorion Sagan. Excerpted by permission of Flatiron Books.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
Preface: What This Book Is About
Prologue: Your Inner Stalker (written by Dorion Sagan)
Introduction: How a Lifelong Obsession with Aging and Health Became My Career (written by Josh Mitteldorf)
You Are Not a Car: You Body Does Not "Wear Out"
The Way of Some Flesh: The Varieties of Aging Experience
Darwin in a Straitjacket: Tracing Modern Evolutionary Theory
Theories of Aging and Aging of Theories
When Aging Was Young: Replicative Senescence
When Aging Was Even Younger: Apoptosis
The Balance of Nature: Demographic Homeostasis
So We All Don't Die at Once: Wiles of the Black Queen
Live Longer Right Now
The Near Future of Aging
All Tomorrow's Parties
Epilogue
Acknowledgments
Glossary
References
Index