I am haunted by a vision in which medical science cures everything and makes everyone immortal—and I am the last person to die before scientists get it right. The New York Times nourishes my vision with frequent reports of promising new treatments for cancer and arteriosclerosis, which jointly account for the great majority of deaths.
The optimism of the Times' science reporters—and their sources in the medical community—contrasts with the pessimism of economists and poets, who continue to focus on the inevitability of death, decay, and depreciation—at least in this world. Gerard Manley Hopkins, for example, in "The Leaden Echo," offered the following analysis and policy prescription:
... no, nothing can be done
To keep at bay
Age and age's evils, hoar hair,
Ruck and wrinkle, drooping, dying, death's worst, winding sheets, tombs and worms and
tumbling to decay;
So be beginning, be beginning to despair.
The poetic invention economists most love to cite is "The Deacon's Masterpiece or the Wonderful One-Hoss Shay," built—according to Oliver Wendell Holmes—so it couldn't break down. A breakdown, you see, requires some part to fail before another. So the deacon deliberately made every part exactly as strong as the rest and rendered that kind of failure impossible. The result?
You see, of course, if you're not a dunce,
How it went to pieces all at once,—
All at once, and nothing first,—
Just as bubbles do when they burst.
Ever since, economists have used the phrase "one-hoss shay depreciation" to describe machinery that works perfectly well right up to the day when it fails beyond repair.
Holmes made gentle fun of the deacon's logic, which led him to write charming poetry but bad economics. The deacon was wiser than Holmes realized. Any designer—whether of a chaise, or an automobile, or a living organism—would be well-advised to make each part roughly as strong as the rest. If the wheels are destined to disintegrate in 80 years, then it's a waste of effort to design a floor that will last for 100. If your car engine won't last past 100,000 miles, you don't need a transmission that will last for 500,000 miles. (There's an exception to this rule for parts that are easily replaceable.)
So to a first approximation, well-designed mechanisms should depreciate just like the wonderful one-hoss shay—all at once and nothing first. The human body, for example, is a well-designed mechanism, thanks to the pressures of natural selection. Therefore (and I believe this observation was first made by the physiologist Jared Diamond in his insightful book The Third Chimpanzee), we should not be surprised that our vision, hearing, mental faculties, physical strength, arteries, and resistance to cancer all tend to deteriorate at around the same time. Nature is a good economist.
Not everything fails at exactly the same time—either in your car or in your body—but that's only because designers can't always predict the exact moment of failure. There is one circumstance in which you'd design a part to last much longer than the whole: when it's just as cheap and easy to make a part long-lived as to make it short-lived. But Diamond argues that such cases are unlikely to arise in the human body. That's because virtually all our organs require routine maintenance, and the frequency of that maintenance is part of the organ's "design." You can always make an organ last longer by maintaining it better, but you can never do that for free because maintenance consumes energy that could otherwise be available for gathering food or fighting predators. If your stomach were designed to last 100 years longer than the rest of you, your body would be well-advised to conserve energy by taking less good care of your stomach—which means your stomach wouldn't last 100 years longer than the rest of you.
The dismal conclusion is that even cures for the big killers—cancer and arteriosclerosis—are unlikely to extend human life spans very much. Because evolution didn't expect you to live past 100, it probably had the good sense not to give you too many organs that will last till 110. To significantly extend your life span, researchers will have to figure out how to extend the lives of all those organs, not just a few. That's not a conclusion I'm happy with, but in the words of Oliver Wendell Holmes, "Logic is logic. That's all I say."