The Body: A Guide for Occupants

by Bill Bryson

And it is surely astounding to reflect that not once in the three billion years since life began has your personal line of descent been broken. For you to be here now, every one of your ancestors had to successfully pass on its genetic material to a new generation before being snuffed out or otherwise sidetracked from the procreative process. That’s quite a chain of success.

There are thousands of things that can kill us—slightly more than eight thousand, according to the International Statistical Classification of Diseases and Related Health Problems compiled by the World Health Organization—and we escape every one of them but one. For most of us, that’s not a bad deal.

As people evolved lighter skin, they also developed lighter-colored eyes and hair—but only pretty recently. Lighter-colored eyes and hair evolved somewhere around the Baltic Sea about six thousand years ago.

To help us deal better with this fractional lag, the brain does a truly extraordinary thing: it continuously forecasts what the world will be like a fifth of a second from now, and that is what it gives us as the present. That means that we never see the world as it is at this very instant, but rather as it will be a fraction of a moment in the future. We spend our whole lives, in other words, living in a world that doesn’t quite exist yet.

Recognition memory explains why so many of us struggle to remember the contents of a book but can often recall where we read the book, the color or design of the cover, and other seeming irrelevancies. Recognition memory is actually useful because it doesn’t clutter the brain with unnecessary details but does help us to remember where we can find those details if we should need them again.

Perhaps nothing is more unexpected about our brains than that they are much smaller today than they were ten thousand or twelve thousand years ago, and by quite a lot. The average brain has shrunk from 1,500 cubic centimeters then to 1,350 cubic centimeters now. That’s equivalent to scooping out a portion of brain about the size of a tennis ball. That’s not at all easy to explain, because it happened all over the world at the same time, as if we agreed to reduce our brains by treaty. The common presumption is that our brains have simply become more efficient and able to pack more performance into a smaller space, rather like cell phones, which have grown more sophisticated as they have contracted in size. But no one can prove that we haven’t simply grown dimmer.

The epiglottis opens when we breathe and closes when we swallow, sending food in one direction and air in another, but occasionally it errs and the results are sometimes dire. It is pretty amazing when you reflect upon it that you can sit at a dinner party enjoying yourself extravagantly—eating, talking, laughing, breathing, slurping wine—and that your nasopharyngeal guardians will send everything to the right place, in two directions, without you having to give it a moment’s consideration.

but the bottom line is that we ended up with brains big enough to handle complex thoughts and vocal tracts uniquely able to articulate them.

Every time you stand up, roughly a pint and a half of your blood tries to drain downward, and your body has to somehow overcome the dead pull of gravity. To manage this, your veins contain valves that stop blood from flowing backward, and the muscles in your legs act as pumps when they contract, helping blood in the lower body get back to the heart. To contract, however, they need to be in motion. That’s why it’s important to get up and move around regularly.

In 1999, just 0.5 percent of children had peanut allergies; today, less than twenty years later, the rate has increased fourfold.

We are in the historically extraordinary position that far more people on Earth suffer from obesity than from hunger.

modern fruits have been selectively bred to be vastly more sugary than they once were.

Modern fruits, for instance, are almost 50 percent poorer in iron than they were in the early 1950s, and about 12 percent down in calcium and 15 percent in vitamin A. Modern agricultural practices, it turns out, focus on high yields and rapid growth at the expense of quality.

no matter how profoundly unconscious we get, or how restless, we almost never fall out of bed, even unfamiliar beds in hotels and the like. We may be dead to the world, but some sentry within us keeps track of where the bed’s edge is and won’t let us roll over it

“There’s also now good data to show that sleep-deprived individuals have higher levels of beta amyloid [a protein associated with Alzheimer’s disease] than those who have slept normally,” Foster told me. “I wouldn’t say that sleep disruption causes Alzheimer’s, but it is probably a contributing factor and may well speed the decline.”

yawn. No one understands why we yawn. Babies yawn in the womb. (They hiccup, too.) People in comas yawn.

Today some 40 percent of us will discover we have cancer at some point in our lives. Many, many more will have it without knowing it and will die of something else first. Half of men over sixty and three-quarters over seventy, for instance, have prostate cancer at death without being aware of it.

America has about 800,000 practicing physicians but needs twice that number of people to administer its payments system.

The problem is that the test for prostate cancer, called a PSA test, is not trustworthy. It measures levels in the blood of a chemical called prostate-specific antigen (PSA). A high PSA reading indicates a possibility of cancer, but only a possibility. The only way of confirming if cancer exists is with a biopsy, which involves sticking a long needle into the prostate via the rectum and withdrawing multiple tissue samples—not a procedure any man is likely to undertake eagerly. Because the needle can only be randomly inserted into the prostate, it is a matter of luck whether it strikes a tumor or not. If it does find a tumor, there is no telling with current technology if the cancer is aggressive or benign. On the basis of this uncertain information, a decision must be made on whether to surgically remove the prostate—a tricky operation with frequently dispiriting consequences—or treat it with radiation. Between 20 and 70 percent of men suffer impotence or incontinence after treatments. One in five experience complications from the biopsy alone. The PSA test is “hardly more effective than a coin toss,” Professor Richard J. Ablin of the University of Arizona has written, and he should know. He was the man who discovered the prostate-specific antigen in 1970. Noting that American men spend at least $3 billion a year on prostate tests, he added, “I never dreamed that my discovery four decades ago would lead to such a profit-driven disaster.” A meta-analysis of six randomized c...

But now it seems we have reached a point of diminishing returns. By one calculation, if we found a cure for all cancers tomorrow, it would add just 3.2 years to overall life expectancy. Eliminating every last form of heart disease would add only 5.5 years. That’s because people who die of these things tend to be old already, and if cancer or heart disease doesn’t get them, something else will. Of nothing is that more true than Alzheimer’s disease. Eradicating it altogether, according to the biologist Leonard Hayflick, would add just nineteen days to life expectancy.

The average person born before 1945 could expect to enjoy only about eight years of retirement before being permanently eliminated from the living, but someone born in 1971 can expect more like twenty years of retirement, and someone born in 1998 can, on current trends, expect perhaps thirty-five years—but all funded in each case by roughly forty years of labor. Most nations haven’t begun to face up to the long-term costs of all these unwell, unproductive people who just go on and on. We have, in short, a lot of problems ahead of us all, both personally and societally.

For those who choose to be buried, decomposition in a sealed coffin takes a long time—between five and forty years, according to one estimate, and that’s only for those who are not embalmed. The average grave is visited for only about fifteen years, so most of us take a lot longer to vanish from the earth than from others’ memories.