Rating: 9/10

Author: Bill Bryson

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Pop science book about the intricacies of our body. It goes deep enough for someone who’s not trained in medicine or biology but shallow enough to keep it interesting and high-level. Really great overview of everything you need to know about our body.


Skin and hair

  • The skin consists of an inner layer called the dermis and an outer epidermis. The outermost surface of the epidermis, called the stratum corneum, is made up entirely of dead cells. It is an arresting thought that all that makes you lovely is deceased.
  • Beneath the epidermis is the more fertile dermis, where reside all the skin’s active systems—blood and lymph vessels, nerve fibers, the roots of hair follicles, the glandular reservoirs of sweat and sebum. Beneath that, and not technically part of the skin, is a subcutaneous layer where fat is stored.
  • The follicles do double duty: they sprout hairs and secrete sebum (from sebaceous glands), which mixes with sweat to form an oily layer on the surface. This helps to keep skin supple and to make it inhospitable for many foreign organisms.
  • An interesting thing about touch is that the brain doesn’t just tell you how something feels, but how it ought to feel. That’s why the caress of a lover feels wonderful, but the same touch by a stranger would feel creepy or horrible. It’s also why it is so hard to tickle yourself.
  • “It is extraordinary how such a small facet of our composition is given so much importance,” she said. “People act as if skin color is a determinant of character when all it is is a reaction to sunlight. Biologically, there is actually no such thing as race—nothing in terms of skin color, facial features, hair type, bone structure, or anything else that is a defining quality among peoples.
  • It has been suggested that light skin may be a consequence of human migration and the rise of agriculture. The argument is that hunter-gatherers got a lot of their vitamin D from fish and game and that these inputs fell sharply when people started growing crops, especially as they moved into northern latitudes. It therefore became a great advantage to have lighter skin, to synthesize extra vitamin D.
  • It is not easy to think of a way that armpit hair enriches human existence. One line of supposition is that secondary hair is used to trap or disperse (depending on theory) sexual scents, or pheromones. The one problem with this theory is that humans don’t seem to have pheromones. A study published in 2017 in Royal Society Open Science by researchers from Australia concluded that human pheromones probably don’t exist and certainly play no detectable role in attraction.
  • A more plausible theory, perhaps, is that secondary hair is for display—that it announces sexual maturity.
  • The uniqueness of fingerprints was first established in the West by the nineteenth-century Czech anatomist Jan Purkinje, though in fact the Chinese had made the same discovery more than a thousand years earlier and for centuries Japanese potters had identified their wares by pressing a finger into the clay before baking.
  • The problem with antibacterial soaps is that they kill good bacteria on your skin as well as bad. The same is true of hand sanitizers.

Microbial you

  • You are home to trillions and trillions of tiny living things.
  • They provide you with about 10 percent of your calories by breaking down foods that you couldn’t otherwise make use of, and in the process extract beneficial nutriments like vitamins B2 and B12 and folic acid.
  • Of the million or so microbes that have been identified, just 1,415 are known to cause disease in humans—very few, all things considered.
  • Surprisingly, the least effective way to spread germs (according to yet another study) is kissing. It proved almost wholly ineffective among volunteers at the University of Wisconsin who had been successfully infected with cold virus.
  • The only really reliable way to transfer cold germs is physically by touch.
  • Altogether as of this writing there are now five groups of giant viruses, which are all not only different from everything else on Earth but also very different from one another. Such strange and foreign bioparticles, it has been argued, are evidence for the existence of a fourth domain of life, in addition to bacteria, archaea, and eukaryotes, the latter of which include complex life like us.
  • Before penicillin, the closest thing to a wonder drug that existed was Salvarsan, developed by the German immunologist Paul Ehrlich in 1910, but Salvarsan was effective against only a few things, principally syphilis, and had a lot of drawbacks. For a start, it was made from arsenic, so was toxic, and treatment consisted in injecting roughly a pint of solution into the patient’s arm once a week for fifty weeks or more. If it wasn’t administered exactly right, fluid could seep into muscle, causing painful and sometimes serious side effects, including the need for amputation. Doctors who could administer it safely became celebrated. Ironically, one of the most highly regarded was Alexander Fleming.
  • Antibiotics are about as nuanced as a hand grenade. They wipe out good microbes as well as bad. Increasing evidence shows that some of the good ones may never recover, to our permanent cost.
  • “From the 1950s through the 1990s,” he says, “roughly three antibiotics were introduced into the U.S. every year. Today it’s roughly one new antibiotic every other year. The rate of antibiotic withdrawals—because they don’t work anymore or have become obsolete—is twice the rate of new introductions. The obvious consequence of this is that the arsenal of drugs we have to treat bacterial infections has been going down. There is no sign of it stopping.”
  • Bacteria never mount an attack until they have assembled sufficient numbers—what is known as a quorum—to make it worthwhile to do so. The idea would be to produce quorum-sensing drugs that wouldn’t kill all bacteria but would just keep their numbers permanently below the threshold, the quorum, that triggers an attack.
  • Another possibility is to enlist bacteriophages, a kind of virus, to hunt down and kill harmful bacteria for us. Bacteriophages—often shortened to just phages—are not well known to most of us, but they are the most abundant bioparticles on Earth.
  • Virtually every surface on the planet, including us, is covered in them. They do one thing supremely well: each one targets a particular bacterium. That means clinicians would have to identify the offending pathogen and select the right phage to kill it, a more costly and time-consuming process, but it would make it much harder for bacteria to evolve resistance.


  • The great paradox of the brain is that everything you know about the world is provided to you by an organ that has itself never seen that world.
  • What is surely most curious and extraordinary about our brain is how largely unnecessary it is. To survive on Earth, you don’t need to be able to write music or engage in philosophy—you really only need to be able to outthink a quadruped—so why have we invested so much energy and risk in producing mental capacity that we don’t really need?
  • 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.
  • Paradoxically, the very fact that the brain is so snugly encased in its protective skull leaves it susceptible to damage when it swells from infection or when fluid is added to it, as with a bleed, because the additional material has nowhere to go. The result is compression of the brain, which can be fatal.


  • Take eyebrows. All the many species of hominids that preceded us had prominent browridges, but we Homo sapiens gave them up in favor of our small, active eyebrows.
  • One theory is that eyebrows are there to keep sweat out of the eyes, but what the eyebrows do really well is convey feelings.
  • There is some evidence to suggest that eyelashes subtly change airflow around the eye, helping to waft away motes of dust and other tiny particulates from landing there, but the main benefit is probably that they add interest and allure to faces. People with long eyelashes are generally rated more attractive than those without.
  • The chin is unique to humans, and no one knows why we have one. It doesn’t seem to confer any structural benefit to the head, so it may be simply that we find a good chin dashing.
  • Victorians so marveled at the intricacy of the eye that they often cited it as proof of intelligent design. It was an odd choice because the eye is really rather the reverse—literally so, for it is built back to front.
  • The rods and cones that detect light are at the rear, but the blood vessels that keep it oxygenated are in front of them. There are vessels and nerve fibers and other incidental detritus all over, and your eye has to see through all this.
  • The iris is what gives the eye its color. It is composed of a pair of muscles that adjust the opening of the pupil, rather like the aperture on a camera, to let in or keep out light as needed.
  • Closer inspection shows that it is in fact “a riot of spots, wedges, and spokes,” in the words of Daniel McNeill, and these patterns are unique to each of us, which is why iris recognition devices are now increasingly used to identify us at security checkpoints.
  • To help protect us from the damage of really loud noises, we have something called an acoustic reflex, in which a muscle jerks the stapes away from the cochlea, essentially breaking the circuit, whenever a brutally intense sound is perceived, and it maintains that posture for some seconds afterward, which is why we are often deafened after an explosion.
  • Unfortunately, the process is not perfect. Like any reflex, it is quick but not instantaneous, and it takes about a third of a second for the muscle to contract, by which point a lot of damage can be done.
  • An interesting and important curiosity of our sense of smell is that it is the only one of the five basic senses not mediated by the hypothalamus. When we smell something, the information, for reasons unknown, goes straight to the olfactory cortex, which is nestled close to the hippocampus, where memories are shaped.

Mouth and throat

  • Just recently it was discovered that saliva also contains a powerful painkiller called opiorphin. It is six times more potent than morphine, though we have it only in very small doses.
  • For years, even textbooks spoke of a tongue map, with the elemental tastes each occupying a well-defined zone: sweet on the tip of the tongue, sour at the sides, bitter at the back. In fact, that is a myth, traced to a textbook written in 1942 by one Edwin G. Boring, a Harvard psychologist who misinterpreted a paper written by a German researcher forty years before that.
  • Altogether we have about ten thousand taste buds, mostly distributed around the tongue, except in the very middle, where there are none at all. Additional taste buds are found in the roof of the mouth and lower down the throat, which is said to be why some medicines taste bitter as they go down.
  • 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.
  • When you eat, most of the aroma reaches you not through your nostrils but by the back staircase of your nasal passage, what is known as the retronasal route, as opposed to the orthonasal route up your nose.
  • Even sound materially influences how delicious we find food. People who are played a range of crunching sounds through headphones while sampling potato chips from various bowls will always rate the crunchier, noisier chips as fresher and tastier, even though all the chips are the same.

Heart and blood

  • The heart is not really one pump but two: one that sends blood to the lungs and one that sends it around the body. The output of the two must be in balance, every single time, for it all to work correctly.
  • Of all the blood pumped out of your heart, the brain takes 15 percent, but actually the greatest amount, 20 percent, goes to the kidneys.
  • Curiously, the blood passing through the chambers of the heart does nothing for the heart itself. The oxygen that nourishes it arrives via the coronary arteries, in exactly the way oxygen reaches other organs.
  • Well into the twentieth century, many medical authorities believed that high blood pressure was a good thing because it indicated vigorous flow.
  • A more difficult question is, What exactly constitutes high blood pressure? For a long time, a reading of 140/90 was generally considered the baseline for hypertension, but in 2017 the American Heart Association surprised nearly everyone by abruptly pushing the number downward to 130/80. That small reduction tripled the number of men and doubled the number of women aged forty-five or under who were deemed to have high blood pressure and lifted practically all people over sixty-five into the danger zone.
  • A heart attack and a cardiac arrest, though usually confused by most of us, are in fact two different things. A heart attack occurs when oxygenated blood can’t get to heart muscle because of a blockage in a coronary artery. Heart attacks are often sudden—that’s why they are called attacks
  • When heart muscle downstream of a blockage is deprived of oxygen, it begins to die, usually within about sixty minutes. Any heart muscle we lose in this way is gone forever, which is a bit galling when you consider that other creatures much simpler than we are—zebra fish, for instance—can regrow damaged heart tissue. Why evolution deprived us of this useful facility is yet another of the body’s many imponderables.
  • Cardiac arrest is when the heart stops pumping altogether, usually because of a failure in electrical signaling.
  • No less appallingly, more than half of all first heart attacks (fatal or otherwise) occur in people who are fit and healthy and have no known obvious risks. They don’t smoke or drink to excess, are not seriously overweight, and do not have chronically high blood pressure or even bad cholesterol readings, but they get a heart attack anyway. Living a virtuous life doesn’t guarantee that you will escape heart problems; it just improves your chances.
  • Karl Landsteiner noticed that when blood from different people was mixed together, sometimes it clumped and sometimes it did not. By noting which samples joined with which others, he was able to divide the samples into three groups, which he labeled A, B, and 0. Although everybody reads and pronounces the last group as the letter O, Landsteiner in fact meant it to be taken as a zero, because it didn’t clump at all.
  • The discovery of blood types explained why transfusions often failed: because the donor and the recipient had incompatible types. It was a hugely significant discovery, but unfortunately almost no one paid any attention to it at the time. Thirty years would pass before Landsteiner’s contribution to medical science was recognized with a Nobel Prize in 1930.
  • The way blood typing works is this: 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. There are some four hundred kinds of antigens altogether, but only a few have an important effect on transfusion, which is why we have all heard of types A, B, AB, and O, but not, say, Kell, Giblett, and type E, to name just a very few among many.
  • We don’t actually know why blood types exist at all. Partly it may be because there simply wasn’t any reason for them not to. That is to say, there was no reason to suppose that any person’s blood would ever end up in someone else’s body, so no reason to evolve mechanisms to deal with such issues. At the same time, by favoring certain antigens in our blood, we can gain improved resistance against particular diseases—though often at a price. People with O blood, for instance, are more resistant to malaria but less resistant to cholera.
  • 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.
  • Your red blood cells, using nitric oxide as their signaling molecule, in large part determine where to dispatch blood as the body’s requirements change from moment to moment. Transfused blood confuses the signaling system. It impedes function.”


  • “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.”
  • One area where testosterone appears not to be doing us men any good at all is longevity. Many factors determine life span, of course, but it is a fact that men who have been castrated live about as long as women do.


  • Until the early years of the twenty-first century, no one knew that bones produced hormones at all, but then a geneticist at Columbia University Medical Center, Gerard Karsenty, realized that osteocalcin, which is produced in bones, not only is a hormone but seems to be involved in a large number of important regulatory activities across the body, from helping to manage glucose levels to boosting male fertility to influencing our moods and keeping our memory in working order. Apart from anything else, it could help to explain the long-standing mystery of how regular exercise helps to stave off Alzheimer’s disease: exercise builds stronger bones and stronger bones produce more osteocalcin.
  • We tend to think of our bones as inert bits of scaffolding, but they are living tissue, too. They grow bigger with exercise and use just as muscles do.


  • Occasionally, as we all know, our body temperature is elevated beyond normal in the condition known as a fever. Curiously, no one knows quite why this happens—whether fevers are an innate defense mechanism aimed at killing invading pathogens or simply a by-product of the body working hard to fight off infection. The question is important because if fever is a defense mechanism, then any effort to suppress or eliminate it may be counterproductive. Allowing a fever to run its course (within limits, needless to say) could be the wisest thing.
  • Children do much better with extreme cold than with extreme heat. Because their sweat glands aren’t fully developed, they don’t sweat freely as adults do. That is in large part why so many of them die so swiftly when left in cars in warm weather.

Immune system

  • “You could look at it and conclude that it’s crazy that the immune system attacks itself,” says Davis. “Alternatively, once you start to think about all that the immune system has to do, it’s surprising that it doesn’t happen all the time. Your immune system is constantly bombarded by things it has never seen before, things that may have only just come into existence—like new flu viruses, which are constantly mutating into new forms. So your immune system has to be able to identify and fight off a more or less infinite number of things.”
  • T cells are a kind of elite corps in the immune system
  • T cells subdivide into two further categories: helper T cells and killer T cells. Killer T cells, as the name suggests, kill cells that have been invaded by pathogens. Helper T cells help other immune cells act, including helping B cells produce antibodies.
  • Memory T cells remember the details of earlier invaders and are therefore able to coordinate a swift response if the same pathogen shows up again—what is known as adaptive immunity.
  • When they identify an invader, they instruct B cells to produce proteins known as antibodies, and these attack the invading organisms. Antibodies are clever things because they recognize and fight off previous invaders quickly if they dare come back. That’s why so many diseases only make you sick once. It is also the process at the heart of vaccination. Vaccination is really a way of inducing the body to produce useful antibodies against a particular scourge without actually making oneself sick.
  • Some infectious agents, like E. coli and salmonella, can trick the immune system into attacking the wrong organisms.
  • 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. Unlike red blood cells, white blood cells can leave the circulatory system to pass through surrounding tissues, like an army patrol searching through jungle.
  • When they encounter an invader, they fire off attack chemicals called cytokines, which is what makes you feel feverish and ill when your body is battling infection. It’s not the infection that makes you feel dreadful, but your body defending itself.
  • “Sometimes,” Michael Kinch, from Washington University in St. Louis, explained to me, “the immune system gets so ramped up that it brings out all its defenses and fires all its missiles in what is known as a cytokine storm. That’s what kills you.
  • Equally bewildering is that autoimmune diseases are grossly sexist. Women are twice as likely as men to get multiple sclerosis, ten times more likely to get lupus, fifty times more likely to suffer a thyroid condition known as Hashimoto’s thyroiditis. Altogether, 80 percent of all autoimmune diseases occur in women.
  • Allergy rates vary across the world from about 10 to 40 percent, with the rates closely following economic performance. The richer the country, the more allergies its citizens get.
  • It may be that people of rich, urbanized nations are more exposed to pollutants—there is evidence that nitrogen oxides from diesel fuels correlate with higher incidences of allergies—or it may be that increased use of antibiotics in the rich nations has directly or indirectly affected our immune responses. Other contributory factors may be lack of exercise and increased obesity.
  • Allergies are not specifically genetic as far as anyone can tell, but your genes can leave you more susceptible to getting certain allergies.
  • The bottom line in either case is that we don’t know why allergies exist at all. Dying from ingesting a peanut is not something that confers any obvious evolutionary benefits, after all, so why this extreme sensitivity has been retained in some humans is, like so much else, a puzzle.

Lungs and breathing

  • The second half of the twentieth century saw a rapid increase in asthma rates in most Western nations, and no one knows why.
  • In China, the city of Guangzhou is highly polluted, while nearby Hong Kong, just an hour away by train, is comparatively clean as it has little industry and lots of fresh air because it is by the sea. Yet in clean Hong Kong, asthma rates are 15 percent, while in heavily polluted Guangzhou they are just 3 percent, exactly the opposite of what one would expect.
  • “All we can really say about asthma is that it is primarily a Western disease,” says Pearce. “There is something about having a Western lifestyle that sets up your immune system in a way that makes you more susceptible. We don’t really understand why.”
  • Cigarette manufacturers introduced filters in the early 1950s. Filters had the great effect that they could claim their cigarettes were now much safer. Most manufacturers charged a premium price for filtered cigarettes, even though the cost of filters was less than the tobacco they displaced. Moreover, most filters didn’t filter out tars and nicotine any better than the tobacco itself had, and to compensate for a perceived loss of taste, the manufacturers started using stronger tobacco. The upshot was that by the late 1950s the average smoker was taking in more tar and nicotine than he had before filters were invented.


  • Vitamins are simply organic chemicals—that is, from things that are or were once alive, like plants and animals—while minerals are inorganic and come from soil or water.
  • In the beginning, vitamins were named in more or less strict alphabetical order—A, B, C, D, and so on—but then the system began to fall apart. Vitamin B was discovered to be not one vitamin but several, and these were renamed B1, B2, B3, and so on up to B12.
  • Then it was decided that the B vitamins weren’t so diverse after all, so some were eliminated and others reclassified, so that today we are left with six semi-sequential B vitamins: B1, B2, B3, B5, B6, and B12.
  • Other vitamins came and went, so that the scientific literature is filled with a lot of what might be called ghost vitamins—M, P, PP, S, U, and several others.
  • Cholesterol is not as fundamentally evil as we tend to think it. Indeed, it is vital to a healthy life. Most of the cholesterol in your body is locked up in your cells, where it is doing useful work. Just a small part—about 7 percent—floats about in the bloodstream. Of that 7 percent, one-third is “good” cholesterol and two-thirds is “bad.
  • The conviction that we should all drink eight glasses of water a day is the most enduring of dietary misunderstandings. The idea has been traced to a 1945 paper from the U.S. Food and Nutrition Board, which noted that that was the amount that the average person consumed in a day. “What happened,” Dr. Stanley Goldfarb of the University of Pennsylvania told the BBC radio program More or Less in 2017, “was that people sort of confused the idea that this was the required intake. And the other confusion that occurred was then people said that it is not so much that you should take in eight ounces eight times a day, but that you should consume that in addition to whatever fluid you consume in association with your diet and your meals. And there was never any evidence for that.”
  • One other enduring myth concerning water intake is the belief that caffeinated drinks are diuretics and make you pee out more than you have taken in. They may not be the most wholesome of options for liquid refreshment, but they do make a net contribution to your personal water balance.
  • Many of our fruits and vegetables are nutritionally less good for us than they were even in the fairly recent past. Donald Davis, a biochemist at the University of Texas, in 2011 compared the nutritive values of various foods in 1950 with those of our own era and found substantial drops in almost every type. 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.


  • Foster found that 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.
  • “What’s really interesting about these third receptors,” Foster told me when we met in his office at Brasenose College, just off the High Street, “is that they function completely independently of sight. As an experiment, we asked a lady who was completely blind—she had lost her rods and cones as a result of a genetic disease—to tell us when she thought the lights in the room were switched on or off. It turned out she was right every time.

Nether regions

  • Sperm pass on none of their mitochondria during conception, so all mitochondrial information is transferred from generation to generation through mothers alone.
  • 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.
  • 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.

Conception and birth

  • It is a curious fact that every woman is born with her lifetime’s supply of eggs already inside her. They are formed when she is still in the womb and sit in the ovaries for years and years before being called into play.
  • A twenty-week-old fetus will weigh no more than three or four ounces but will already have 6 million eggs inside her. That number falls to 1 million by the time of birth and continues to fall, though at a slower rate, through life. As she enters her childbearing years, a woman will have about 180,000 eggs primed and ready to go.
  • Only belatedly have researchers come to realize that the placenta does much more than just filter wastes and pass on oxygen. It takes an active role in the development of the child: stops toxins from passing from the mother to the fetus, kills parasites and pathogens, distributes hormones, and does everything it can to compensate for maternal deficiencies—if, say, the mother smokes or drinks or stays up too late.
  • The average woman’s birth canal is about an inch narrower than the width of the average newborn’s head, making it the most painful inch in nature. To squeeze through this constricted space, the baby must execute an almost absurdly challenging ninety-degree turn as it proceeds through the pelvis. If ever there was an event that challenges the concept of intelligent design, it is the act of childbirth. No woman, however devout, has ever in childbirth said, “Thank you, Lord, for thinking this through for me.”
  • 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.
  • Cesarean babies eventually acquire the same mix of microbes as those born vaginally—by a year their microbiota are usually indistinguishable—but there is something about those initial exposures that makes a long-term difference. No one has figured out quite why that should be.
  • On top of all that, about four women in every ten are given antibiotics during delivery, which means that doctors are declaring war on babies’ microbes just as they are acquiring them. We’ve no idea what consequences this has for their long-term health, but it’s unlikely to be good.
  • In 1986, Professor David Barker of the University of Southampton in England proposed what has become known as the Barker hypothesis or, a little less snappily, the theory of fetal origins of adult disease. Barker, an epidemiologist, posited that what happens in the womb can determine health and well-being for the rest of one’s life.
  • Most authorities now extend that period of crucial vulnerability from the moment of your conception to your second birthday—what has become known as the first thousand days. That means that what happens to you in this comparatively brief, formative period of your life can powerfully influence how comfortably alive you are decades later.
  • It has been suggested that children growing up today will be the first in modern history to live shorter, less healthy lives than those of their parents. We aren’t just eating ourselves into early graves, it seems, but breeding children to jump in alongside us.


  • Perversely, farming didn’t bring improved diets but almost everywhere poorer ones. Focusing on a narrower range of staple foods meant most people suffered at least some dietary deficiencies, without necessarily being aware of it. Moreover, living in proximity to domesticated animals meant that their diseases became our diseases.


  • It has been suggested, in fact, that if all men lived long enough, they would all get prostate cancer.
  • What it comes down to really is cancer is, appallingly, your own body doing its best to kill you. It is suicide without permission.
  • Cancer cells are just like normal cells except that they are proliferating wildly. Because they are so seemingly normal, the body sometimes fails to detect them and doesn’t invoke an inflammatory response as it would with a foreign agent. That means that most cancers in their early stages are painless and invisible. It is only when tumors grow big enough to press on nerves or form a lump that we become aware that something is wrong. Some cancers can quietly accrete for decades before they become evident. Others never become evident at all.
  • 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.”
  • “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.”
  • Lifestyle is a huge factor in determining which of us get cancer. More than half of cases, by some calculations, are caused by things we can do something about—smoking, drinking to excess, and overeating primarily.


  • Mammograms are in fact fuzzy things. Reading them accurately is a challenging task—much more challenging than even many medical professionals realize. As Timothy J. Jorgensen has noted, when 160 gynecologists were asked to assess the likelihood of a fifty-year-old woman having breast cancer if her mammogram was positive, 60 percent of them thought the chances were 8 or 9 out of 10. “The truth is that the odds the woman actually has cancer are only 1 in 10,” writes Jorgensen.
  • The unfortunate bottom line is that breast cancer screening doesn’t save a lot of lives. For every thousand women screened, four will die of breast cancer anyway (either because the cancer was missed or because it was too aggressive to be treated successfully). For every thousand women who are not screened, five will die of breast cancer. So screening saves one life in every thousand.
  • 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
  • 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.
  • All this isn’t to say that men should absolutely avoid PSA tests or women breast cancer screening. For all their flaws, they are the best tools available, and they do indubitably save lives. But those undergoing screenings should perhaps be made more aware of the shortcomings.

The end

  • In 1961, Leonard Hayflick, then a young researcher at the Wistar Institute in Philadelphia, made a discovery that nearly everyone in his field found impossible to accept. He discovered that 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.
  • But then a team of researchers at the University of California at San Francisco discovered that stretches of 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. With this finding, the Hayflick limit suddenly became credible.
  • Alas, years of subsequent research have shown that telomere shortening can account for only a small part of the process. After the age of sixty, the risk of death doubles every eight years. A study by geneticists at the University of Utah found that telomere length may account for as little as 4 percent of that additional risk.
  • Telomere chemistry is regulated by an enzyme called telomerase, which switches off the cell when it has reached its preset quota of divisions. In cancerous cells, however, telomerase doesn’t instruct the cells to stop dividing, but rather lets them go on proliferating endlessly. This has raised the possibility that a way to fight cancer would be to target telomerase in the cells.Free radicals are wisps of cellular waste that build up in the body in the process of metabolism. They are a by-product of our breathing oxygen. As one toxicologist has put it, “The biochemical price of breathing is aging.”
  • The chances of reaching your 110th birthday are about one in seven million. It helps a lot to be a woman; they are ten times more likely to reach 110 than a man. It is an interesting fact that women have always outlived men.
  • Yet in every period in history, in every society examined, women have always lived several years longer on average than men. And they still do now, even though men and women are subjected to more or less identical health care.
  • Moreover, people in one of the poorest regions of Costa Rica, the Nicoya Peninsula, live longest of all, even though they have much higher rates of obesity and hypertension. They also have longer telomeres. The theory is that they benefit from closer social bonds and family relationships. Curiously, it was found that if they live alone or don’t see a child at least once a week, the telomere length advantage vanishes. Itis an extraordinary fact that having good and loving relationships physically alters your DNA. Conversely, a 2010 U.S. study found, not having such relationships doubles your risk of dying from any cause.
  • According to a 2014 study in the Journal of Palliative Medicine, between 50 and 60 percent of terminally ill patients report having intense but highly comforting dreams about their impending passing. A separate study found evidence of a surge of chemicals in the brain at death, which may account for the intense experiences often reported by survivors of near-death incidents.