“The Body: A Guide for Occupants” by Bill Bryson

  1. Memory is not a fixed and permanent record, like a document in a filing cabinet. It is something much more hazy and mutable. As Elizabeth Loftus told an interviewer in 2013, “It’s a little more like a Wikipedia page. You can go in there and change it, and so can other people.”
  2. Declarative memory is the kind you can put into words—the names of state capitals, your date of birth, how to spell “ophthalmologist,” and everything else you know as fact. Procedural memory describes the things you know and understand but couldn’t so easily put into words—how to swim, drive a car, peel an orange, identify colors.
  3. The nucleus accumbens, a region of the forebrain associated with pleasure, grows to its largest size in one’s teenage years. At the same time, the body produces more dopamine, the neurotransmitter that conveys pleasure, than it ever will again. That is why the sensations you feel as a teenager are more intense than at any other time of life. But it also means that seeking pleasure is an occupational hazard for teenagers.
  4. Ekman concluded that six expressions are universal: fear, anger, surprise, pleasure, disgust, and sorrow.
  5. No society has ever been found that doesn’t respond to smiles in the same way. True smiles are brief—between two-thirds of a second and four seconds. That’s why a held smile begins to look menacing. A true smile is the one expression that we cannot fake.
  6. Floaters are a common occurrence as you get older, and are generally harmless, though they can indicate a retinal tear. The technical name for them, if you wish to impress someone, is muscae volitantes, or “hovering flies.”
  7. Tears come in three varieties: basal, reflex, and emotional. Basal are the functional ones that provide lubrication. Reflex tears are those that emerge when the eye is irritated by smoke or sliced onions or similar. And emotional tears are of course self-evident, but they are also unique. We are the only creatures that cry from feeling, as far as we can tell. Why we do so is another of life’s many mysteries. We get no physiological benefit from erupting in tears. It is also a little odd surely that this act signifying powerful sadness is also triggered by extreme joy or quiet rapture or intense pride or almost any other potent emotional state.
  8. Heimlich seriously undermined his reputation by championing a treatment called malaria therapy, in which people were purposely infected with low doses of malaria in the belief that it would cure them of cancer, Lyme disease, and AIDS, among much else. His claims for the treatment were not supported by any actual science. Partly because he had become an embarrassment, in 2006 the American Red Cross stopped using the term “Heimlich maneuver” and started calling it “abdominal thrusts.”
  9. As well as the mouth, the body has taste receptors in the gut and throat (to help identify spoiled or toxic substances), but they don’t connect to the brain in the same way as the taste receptors on your tongue, and for good reason. You don’t want to taste what your stomach is tasting. Taste receptors have also been found in the heart, the lungs, and even the testicles. No one knows quite what they are doing there. They also send signals to the pancreas to adjust insulin output, and it may be connected to that.
  10. ou experience the world that your brain allows you to experience.
  11. Well into the nineteenth century most doctors approached diseases not as distinct afflictions, each requiring its own treatment, but as generalized imbalances affecting the whole body.
  12. That was the problem with bleeding. If you could tell yourself that those who survived did so because of your efforts while those who died were beyond salvation by the time you reached them, bleeding would always seem a prudent option.
  13. All blood cells are the same inside, but the outsides are covered with different kinds of antigens—that is, proteins that project outward from the cell surface—and that is what accounts for blood types.
  14. People with O blood, for instance, are more resistant to malaria but less resistant to cholera. By developing a variety of blood types and spreading them around among populations, we benefit the species, if not always the individuals within it.
  15. When a blood bank receives a call for blood, it normally dispatches the oldest blood first, to use up aging stock before it expires, which means that almost everybody receives old blood. Worse still, it was discovered that even fresh transfused blood actually impedes the performance of existing blood in the recipient’s body. This is where nitric oxide comes in.
  16. The term “stent” has a curious history. It is named after Charles Thomas Stent, a nineteenth-century London dentist who had nothing to do with heart surgery. Stent was the inventor of a compound used to make dental molds, which oral surgeons eventually also found useful when doing repairs to the mouths of soldiers wounded in the Boer War. Over time, the term came to be used for any kind of device used to keep tissue in place during corrective surgery and, in the absence of a better term, gradually took up a position as the word of choice for an arterial support for cardiac surgery.
  17. Our blood is red, incidentally, why do our veins look blue? It is simply a quirk of optics. When light lands on our skin, a higher proportion of the red spectrum is absorbed, but more of the blue light is bounced back, so blue is what we see. Color is not some innate feature that radiates out of an object but rather a marker of the light bouncing off it.
  18. Rh factor is the name for a kind of surface protein called an antigen. People who have the Rh antigen (about 84 percent of us) are said to be Rh-positive. Those who lack it, the remaining 16 percent, are Rh-negative.
  19. A central part of the problem is that our bodies evolved to deal with the challenge of dietary paucity, not overabundance. So leptin isn’t programmed to tell you to stop eating. Nothing chemical in your body is. That’s a big part of why you tend to just keep on consuming. We are habituated into devouring foods greedily whenever we are able on the assumption that abundance is an occasional condition.
  20. If your hormones think you are starving, those processes will not be allowed to begin. That’s why young people who are anorexic often have a very delayed start to puberty. “It’s also almost certainly why puberty starts years earlier now than it did in historic times,” says Wass. “In Henry VIII’s reign, puberty started at sixteen or seventeen. Now it is more commonly eleven. That’s almost certainly because of improved nutrition.”
  21. The humors were believed to be fluids that circulated within the body and kept everything in balance. For two thousand years, a belief in humors was used to explain people’s health, looks, tastes, disposition—everything. In this context, humor has nothing to do with amusement. It comes from a Latin word for “moisture.” When we talk today of humoring someone or of people being ill-humored, we are not talking about their capacity for laughter, at least not etymologically.
  22. Not less than two hours a day should be devoted to exercise and the weather should be little regarded. If the body be feeble, the mind will not be strong. —THOMAS JEFFERSON
  23. You may think your legs drop straight down from your waist—they do in apes—but in fact the femur angles inward as it descends from pelvis to knee. This has the effect of moving our lower legs closer together, giving us a much smoother, more graceful gait. No ape can be trained to walk like a human. They are compelled by their bone structure to waddle, and to do so in a most inefficient way.
  24. “If you want to understand the human body, you have to understand that we evolved to be hunter-gatherers. That means being prepared to expend a lot of energy to acquire food, but not wasting energy when you don’t need to.” So exercise is important, but rest is vital, too.
  25. One big problem with exercise is that we don’t track it very scrupulously. One study in America found that people overestimate the number of calories they burned in a workout by a factor of four. They also then consumed, on average, about twice as many calories as they had just burned off.
  26. Lean people tend to spend two and a half hours more a day on their feet than fat people, not consciously exercising, but just moving about, and it was this that kept them from accumulating fat.
  27. 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.
  28. 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.
  29. We could reduce our energy needs considerably if we elected to be cold-blooded. A typical mammal uses about thirty times as much energy in a day as a typical reptile, which means that we must eat every day what a crocodile needs in a month.
  30. It is a great irony nonetheless that a very high proportion of the suffering we do is inflicted on us by our own defenses in the form of autoimmune diseases like multiple sclerosis, lupus, rheumatoid arthritis, Crohn’s disease, and many unappealing others.
  31. Inflammation is essentially the heat of battle as the body defends itself from damage. Blood vessels in the vicinity of an injury dilate, allowing more blood to flow to the site, bringing with it white blood cells to fight off invaders. That causes the site to swell, increasing the pressure on surrounding nerves, resulting in tenderness.
  32. Though he didn’t use the term “hygiene hypothesis.” That came later. The idea, very loosely, is that children in the developed world grow up in much cleaner environments than children of earlier ages did, and so don’t develop resistance to infection as well as those who have a more intimate contact with dirt and parasites.
  33. Efficiency is also assisted by a slight differential in air pressure between the outside world and the space around your lungs, known as the pleural cavity. Air pressure in the chest is less than atmospheric pressure, which helps to keep the lungs inflated. If air gets into the chest, because of a puncture wound, say, the differential vanishes and the lungs collapse to only about a third of their normal size.
  34. The greatest of vitamin controversies was stirred up by the American chemist Linus Pauling (1901–94), who had the distinction of winning not one but two Nobel Prizes (for chemistry in 1954 and for peace eight years later). Pauling believed that massive doses of vitamin C were effective against colds, flu, and even some cancers. He took up to forty thousand milligrams of vitamin C daily (the recommended daily dose is sixty milligrams) and maintained that his large intake of vitamin C had kept his prostate cancer at bay for twenty years. He had no evidence for any of his claims, and all have been pretty well discredited by subsequent studies. Thanks to Pauling, to this day many people believe that taking a lot of vitamin C will help to get rid of a cold. It won’t.
  35. A small but unspecified number of amino acids strung together is a peptide. Ten or twelve strung together is a polypeptide. When a polypeptide begins to get bigger than that, it becomes, at some ineffable point, a protein.
  36. Eight of the twenty amino acids cannot be made in the body and must be consumed in the diet. If they are missing from the foods we eat, then certain vital proteins cannot be made.
  37. The main thing to bear in mind is that carbohydrates, upon being digested, are just more sugar—often quite a lot more. That means that a 150-gram serving of white rice or a small bowl of cornflakes will have the same effect on your blood glucose levels as nine teaspoons of sugar.
  38. When fats are broken down in the body, they are teamed up with cholesterol and proteins in a new molecule called lipoproteins, which travel through the body via the bloodstream. Lipoproteins come in two principal types: high density and low density. Low-density lipoproteins are the ones frequently referred to as “bad cholesterol” because they tend to form plaque deposits on the walls of blood vessels.
  39. The human body likes to hold on to its fat. It burns some of the fat we consume for energy, but a good deal of the rest is sent off to tens of billions of tiny storage terminals called adipocytes, which exist all over the body. The upshot of all this is that the human body is designed to take in fuel, use what it needs, and store the rest to call on later as required. That makes it possible for us to be active for hours at a time without eating. Your body below the neck doesn’t do a lot of complicated thinking, and it is only too happy to hold on to any surplus fat you give it. It even rewards you for overeating with a lovely feeling of well-being.
  40. We live in a paradoxical situation. For centuries, people ate unhealthily out of economic necessity. Now we do it out of choice.
  41. When America joined the Second World War, the War Department commissioned Keys to devise a lightweight food pack for paratroopers. The result was the imperishable army food known as K rations. The K stood for Keys.
  42. Three apples would give you just as much sugar but compensate by also giving you vitamins, minerals, and fiber, not to mention a greater feeling of satiation. That said, even the apples are a lot sweeter than they really need to be. As Lieberman has noted, modern fruits have been selectively bred to be vastly more sugary than they once were. The fruits that Shakespeare ate were, for the most part, probably no sweeter than the modern carrot.
  43. When food reaches the consistency of pea soup, it is known as chyme (pronounced “kime”). The rumblings of your gut, incidentally, come mostly from the large intestine, not the stomach. The technical term for gut rumblings is “borborygmi.”
  44. The smell of a fart is composed largely of hydrogen sulfide, even though hydrogen sulfide accounts for only about one to three parts per million of what is expelled. Hydrogen sulfide in concentrated form—as in sewage gas—can be highly lethal, but why we are so sensitive to it in trace exposures is a question science has yet to answer. Curiously, we don’t smell it at all when it rises to lethal levels.
  45. Some birds and marine mammals are able to switch off one half of their brain at a time, so that one half remains alert while the other is snoozing.
  46. As well as normal overnight sleep, we also commonly indulge in snatches of wakeful-hours sleep in a state known as hypnagogia, a netherworld between waking and unconsciousness, often without being aware of it. Alarmingly, when a dozen airline pilots on long-haul flights were studied by sleep scientists, almost all were found to have been asleep, or all but asleep, at various times during the flight without realizing it.
  47. Our eyes contain a third photoreceptor cell type in addition to the well-known rods and cones. These additional receptors, known as photosensitive retinal ganglion cells, have nothing to do with vision but exist simply to detect brightness—to know when it is daytime and when night. They pass this information on to two tiny bundles of neurons within the brain, roughly the size of a pinhead, embedded in the hypothalamus and known as suprachiasmatic nuclei. These two bundles (one in each hemisphere) control our circadian rhythms. They are the body’s alarm clocks. They tell us when to rise and shine and when to call it a day.
  48. The pressure to sleep grows more intense the longer we stay awake. This is in large part a consequence of an accumulation of chemicals in the brain as the day goes by, in particular one called adenosine, which is a by-product of the output of ATP (or adenosine triphosphate), the little molecule of intense energy that powers our cells. The more adenosine you accumulate, the drowsier you feel.
  49. The average ejaculation is about three milliliters, which means that a typical sex act produces enough sperm to repopulate a medium-sized country at the very least. Why there is such a broad range of wriggling potentiality, and indeed why such an extravagance of production even at the lower end when only one sperm is required for conception, are questions that science has yet to answer.
  50. One intriguing paradox of reproduction is that women are having babies later but preparing for it earlier. The age of first menstruation for women has fallen from fifteen in the late nineteenth century to just twelve and a half today, at least in the West. That is almost certainly because of improved nutrition.
  51. You leave the womb sterile, or so it is generally thought, but are liberally swabbed with your mother’s personal complement of microbes as you move through the birth canal. We are only beginning to understand the importance and nature of a woman’s vaginal microbiome. Babies born by Cesarean section are robbed of this initial wash. The consequences for the baby can be profound. Various studies have found that people born by C-section have substantially increased risks for type 1 diabetes, asthma, celiac disease, and even obesity and an eightfold greater risk of developing allergies.
  52. Pain is a strange and troublesome thing. Nothing in your life is more necessary and less welcome.
  53. Nociceptors respond to three kinds of painful stimuli: thermal, chemical, and mechanical, or at least so it is universally assumed. Remarkably, scientists have not yet found the nociceptor that responds to mechanical pain. It is extraordinary surely that when you whack your thumb with a hammer or prick yourself with a needle, we don’t know what actually happens beneath your outer surface. All that can be said is that signals from all types of pain are conveyed on to the spinal cord and brain by two different types of fibers—fast-conducting A delta fibers (they’re coated in myelin, so slicker, as it were) and slower-acting C fibers. The swift A delta fibers give you the sharp ouch of a hammer blow; the slower C fibers give you the throbbing pain that follows.
  54. Several of your nociceptors are polymodal, which means they are triggered by different stimuli. That’s why spicy foods taste hot, for instance.
  55. The central nervous system is the brain and spinal cord. The nerves radiating out from this central hub—the ones that reach out to the other parts of your body—are the peripheral nervous system. The nervous system is additionally divided by function into the somatic nervous system, which is the part that controls voluntary actions (like scratching your head), and the autonomic nervous system, which controls all those things like heartbeats that you don’t have to think about because they are automatic. The autonomic nervous system is further divided into sympathetic and parasympathetic systems. The sympathetic is the part that responds when the body needs sudden actions—what is generally referred to as the fight-or-flight response. The parasympathetic is sometimes referred to as the “rest and digest” or “feed and breed” system and looks after a miscellany of other, generally less urgent matters like digestion and waste disposal, the production of saliva and tears, and sexual arousal (which may be intense but not urgent in the fight-or-flight sense).
  56. Wall singled out cancer pain as “the apogee of pointlessness.” Most cancers don’t cause pain in their early stages when it might usefully alert us to take remedial action. Instead, all too often cancer pain becomes evident only when it is too late to be useful.
  57. “Acute pain has an obvious point: it tells you that something is wrong and needs attention. They wanted chronic pain to have that kind of point, too—to exist for a purpose. But chronic pain has no purpose. It’s just a system gone wrong, in the same way that cancer is a system gone wrong.
  58. Studies have shown that people given a colored tablet with corners will report feeling better than when given a plain white tablet. Red pills are deemed more fast acting than white pills. Green and blue pills have a more soothing effect.
  59. For 90 percent of rare diseases, there are no treatments at all.
  60. Medical care is actually making things worse by treating the symptoms of mismatch diseases so effectively that we “unwittingly perpetuate their causes.”
  61. Cancer is quite unlike other maladies. It is often relentless in its attacks. Victory against it is nearly always hard won and often at great cost to the victim’s overall health. It will retreat under an onslaught, regroup, and return in a more potent form. Even when seemingly defeated, it may leave behind “sleeper” cells that can lie dormant for years before springing to life again. Above all, cancer cells are selfish. Normally, human cells do their job, then die on command when instructed to by other cells for the good of the body. Cancer cells don’t. They proliferate entirely in their own interests.
  62. Something we have only recently realized is that before cancers metastasize, they are able to prepare the ground for an invasion in distant target organs, probably through some form of chemical signaling. “What this means,” Vormoor says, “is that when cancer cells spread to other organs, they don’t just turn up and hope for the best. They already have a base camp in the destination organ. Why certain cancers go to certain organs, often in distant parts of the body, has always been a mystery.”
  63. “Cancer is the price we pay for evolution. If our cells couldn’t mutate, we would never get cancer, but we also couldn’t evolve. We would be fixed forever. What this means in practice is that although evolution is sometimes tough on the individual, it’s beneficial for the species.”
  64. Mustard gas dramatically slowed the creation of white blood cells in those exposed to it. From this, it was realized that some derivative of mustard gas might be useful in treating some cancers. Thus was born chemotherapy.
  65. Originally “cancer” described any non-healing sore, from which it is related to “canker.” In its more specific modern sense, it dates from the sixteenth century. The word comes from the Latin for “crab” (which is why the celestial constellation and its associated zodiac sign are called Cancer). It is said that Hippocrates, the Greek physician, used the term for tumors because their shape reminded him of crabs.
  66. 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.
  67. America has about 800,000 practicing physicians but needs twice that number of people to administer its payments system.
  68. For most of history the focus of medicine has been to make sick people better, but now increasingly doctors devote their energies to trying to head off problems before they even arise, through programs of screening and the like, and that changes the dynamics of care entirely. There is an old joke in medicine that seems especially apt here: Q. What is the definition of a well person? A. Someone who hasn’t been examined yet.
  69. We live in an age in which we are killed, more often than not, by lifestyle.
  70. Cultured human stem cells—that is, cells grown in a lab, as opposed to in a living body—can divide only about fifty times before they mysteriously lose their power to go on. In essence, they appear to be programmed to die of old age. The phenomenon became known as the Hayflick limit.
  71. Specialized DNA at the end of each chromosome called telomeres fulfill the role of tallying device. With each cell division, telomeres shorten until eventually they reach a predetermined length (which varies markedly from one cell type to another) and the cell dies or becomes inactive.
  72. The mother hypothesis is that childbearing is dangerous and exhausting, and it becomes more of both as women age. So menopause may simply be a kind of protection strategy. By no longer having the wear and distraction of further childbirth, a woman can better focus on maintaining her own health while completing the rearing of her children just as they are entering their most productive years. This leads naturally to the grandmother hypothesis, which is that women stop breeding in middle age so that they can help their offspring raise their children.
  73. Reaching 80 is largely a consequence of following a healthy lifestyle, but after that it is almost entirely a matter of genes.
  74. It is an extraordinary fact that having good and loving relationships physically alters your DNA.
  75. Studies have shown that cancer sufferers receiving palliative care in their final weeks rather than chemotherapy actually live longer and suffer much less.


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