22
" Most of us have experienced that abrupt feeling of falling while asleep known as a hypnic or myoclonic jerk. No one knows why we have this sensation. One theory is that it goes back to the days when we slept in trees and had to take care not to fall off. The jerk may be a kind of fire drill. That may seem far-fetched, but it is a curious fact, when you think about it, that 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 (except in unusually drunk or fevered circumstances). Some part of us, it seems, pays heed to the outside world, even for the heaviest sleepers. "
― Bill Bryson , The Body: A Guide for Occupants
27
" The second thing that can be said with regard to life expectancy is that it is not a good idea to be an American. Compared with your peers in the rest of the industrialized world, even being well-off doesn’t help you here. A randomly selected American aged forty-five to fifty-four is more than twice as likely to die, from any cause, as someone from the same age-group in Sweden. Just consider that. If you are a middle-aged American, your risk of dying before your time is more than double that of a person picked at random off the streets of Uppsala or Stockholm or Linköping. It is much the same when other nationalities are brought in for comparison. For every 400 middle-aged Americans who die each year, just 220 die in Australia, 230 in Britain, 290 in Germany, and 300 in France. These health deficits begin at birth and go right on through life. Children in the United States are 70 percent more likely to die in childhood than children in the rest of the wealthy world. Among rich countries, America is at or near the bottom for virtually every measure of medical well-being—for chronic disease, depression, drug abuse, homicide, teenage pregnancies, HIV prevalence. Even sufferers of cystic fibrosis live ten years longer on average in Canada than in the United States. What is perhaps most surprising is that all these poorer outcomes apply not just to underprivileged citizens but to prosperous white college-educated Americans when compared with their socioeconomic equivalents abroad. "
― Bill Bryson , The Body: A Guide for Occupants
30
" Sperm pass on none of their mitochondria during conception, so all mitochondrial information is transferred from generation to generation through mothers alone. Such a system means that there will be many extinctions along the way. A woman endows all her children with her mitochondria, but only her daughters have the mechanism to pass it onward to future generations. So if a woman has only sons or no children at all—and that happens quite often, of course—her personal mitochondrial line will die with her. All her descendants will still have mitochondria, but it will come from other mothers on other genetic lines. In consequence, the human mitochondrial pool shrinks a little with every generation because of these localized extinctions. Over time, the mitochondrial pool for humans has shrunk so much that, almost unbelievably but rather wonderfully, we are all now descended from a single mitochondrial ancestor—a woman who lived in Africa about 200,000 years ago. You might have heard her referred to as Mitochondrial Eve. She is, in a sense, mother of us all. "
― Bill Bryson , The Body: A Guide for Occupants
31
" Our eyes contain two types of photoreceptors for vision—rods, which help us see in dim conditions but provide no color, and cones, which work when the light is bright and divide the world up into three colors: blue, green, and red. People who are “color-blind” normally lack one of the three types of cones, so they don’t see all the colors, just some of them. People who have no cones at all, and are genuinely color-blind, are called achromatopes. Their main problem isn’t that their world is pallid but that they really struggle to cope with bright light and can be literally blinded by daylight. Because we were once nocturnal, our ancestors gave up some color acuity—that is, sacrificed cones for rods—to gain better night vision. Much later, primates re-evolved the ability to see reds and oranges, the better to identify ripe fruit, but we still have just three kinds of color receptors compared with four for birds, fish, and reptiles. It’s a humbling fact, but virtually all nonmammalian creatures live in a visually richer world than we do. "
― Bill Bryson , The Body: A Guide for Occupants
34
" Where America really differs from other countries is in the colossal costs of its health care. An angiogram, a survey by The New York Times found, costs an average of $914 in the United States, $35 in Canada. Insulin costs about six times as much in America as it does in Europe. The average hip replacement costs $40,364 in America, almost six times the cost in Spain, while an MRI scan in the United States is, at $1,121, four times more than in the Netherlands. The entire system is notoriously unwieldy and cost-heavy. America has about 800,000 practicing physicians but needs twice that number of people to administer its payments system. The inescapable conclusion is that higher spending in America doesn’t necessarily result in better medicine, just higher costs. "
― Bill Bryson , The Body: A Guide for Occupants
35
" Bowel transit time, as it is known in the trade, is a very personal thing and varies widely between individuals, and in fact within individuals depending on how active they are on a given day and what and how much they have been eating. Men and women evince a surprising amount of difference in this regard. For a man, the average journey time from mouth to anus is fifty-five hours. For a woman, typically, it is more like seventy-two. Food lingers inside a woman for nearly a full day longer, with what consequences, if any, we do not know.
Roughly speaking, however, each meal you eat spends about four to six hours in the stomach, a further six to eight hours in the small intestine, where all that is nutritious (or fattening) is stripped away and dispatched to the rest of the body to be used or, alas, stored, and up to three days in the colon, which is essentially a large fermentation tank where billions and billions of bacteria pick over whatever the rest of the intestines couldn’t manage—fiber mostly. That’s why you are constantly told to eat more fiber: because it keeps your gut microbes happy and at the same time, for reasons not well understood, reduces the risk of heart disease, diabetes, bowel cancer, and indeed death of all types. "
― Bill Bryson , The Body: A Guide for Occupants
36
" Heat is lost at the surface, so the more surface area you have relative to volume, the harder you must work to stay warm. That means that little creatures have to produce heat more rapidly than large creatures. They must therefore lead completely different lifestyles. An elephant’s heart beats just thirty times a minute, a human’s sixty, a cow’s between fifty and eighty, but a mouse’s beats six hundred times a minute—ten times a second. Every day, just to survive, the mouse must eat about 50 percent of its own body weight. We humans, by contrast, need to consume only about 2 percent of our body weight to supply our energy requirements. One area where animals are curiously—almost eerily—uniform is with the number of heartbeats they have in a lifetime. Despite the vast differences in heart rates, nearly all animals have about 800 million heartbeats in them if they live an average life. The exception is humans. We pass 800 million heartbeats after twenty-five years, and just keep on going for another fifty years and 1.6 billion heartbeats or so. It is tempting to attribute this exceptional vigor to some innate superiority on our part, but in fact it is only over the last ten or twelve generations that we have deviated from the standard mammalian pattern thanks to improvements in our life expectancy. For most of our history, 800 million beats per lifetime was about the human average, too. "
― Bill Bryson , The Body: A Guide for Occupants
40
" Altogether it takes 7 billion billion billion (that’s 7,000,000,000,000,000,000,000,000,000, or 7 octillion) atoms to make you. No one can say why those 7 billion billion billion have such an urgent desire to be you. They are mindless particles, after all, without a single thought or notion between them. Yet somehow for the length of your existence, they will build and maintain all the countless systems and structures necessary to keep you humming, to make you you, to give you form and shape and let you enjoy the rare and supremely agreeable condition known as life. "
― Bill Bryson , The Body: A Guide for Occupants
