The Story of the Human Body by Daniel Lieberman Flashcards
(417 cards)
1
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This book, however, argues that our society’s general failure to think about human evolution is a major reason we fail to prevent preventable diseases.76
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the most potent form of evolution is not biological evolution of the sort described by Darwin, but cultural evolution, in which we develop and pass on new ideas and behaviors to our children, friends, and others.83
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The monkey in question, an escaped rhesus macaque, had been living for more than three years on the city’s streets scavenging food from Dumpsters and trash cans, dodging cars, and cleverly evading capture by frustrated wildlife officials. It became a local legend.111
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the monkey epitomizes how some animals survive superbly in conditions for which they were not originally adapted.120
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You and I exist about as far removed from our natural environment as the Mystery Monkey. More than six hundred generations ago, everybody everywhere was a hunter-gatherer. Until relatively recently—the blink of an eye in evolutionary time—your ancestors lived in small bands of fewer than fifty people. They moved regularly from one camp to the next, and they survived by foraging for plants as well as hunting and fishing. Even after agriculture was invented starting about 10,000 years ago, most farmers still lived in small villages, labored daily to produce enough food for themselves,126
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6
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wouldn’t we enjoy better health if we ate the foods we were adapted to consume and exercised as our ancestors used to?165
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if you ate and exercised more like your Stone Age ancestors. You can start by adopting a “paleodiet.” Eat plenty of meat (grass-fed, of course), as well as nuts, fruits, seeds, and leafy plants, and shun all processed foods with sugar and simple starches. If you are really serious, supplement your diet with worms, and never eat grains, dairy products, or anything fried. You can also incorporate more Paleolithic activities into your daily routine. Walk or run 10 kilometers (6.2 miles) a day (barefoot, of course), climb a few trees, chase squirrels in the park, throw rocks, eschew chairs, and sleep on a board instead of a mattress.168
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Natural selection is a remarkably simple process that is essentially the outcome of three common phenomena. The first is variation: every organism differs from other members of its species.195
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The second phenomenon is genetic heritability: some of the variations present in every population are inherited because parents pass their genes on to their offspring.197
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The third and final phenomenon is differential reproductive success: all organisms, including humans, differ in how many offspring they produce who, themselves, survive to reproduce.200
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If you agree that variation, heritability, and differential reproductive success occur, then you must accept that natural selection occurs, because the inevitable outcome of these combined phenomena is natural selection.205
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12
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a third of your genome has no apparent function but exists because it somehow got added or lost its function over eons.8 Your phenotype (your observable traits, such as the color of your eyes or the size of your appendix) is also replete with features that perhaps once had a useful role but no longer do, or which are simply the by-products of the way you developed.233
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13
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what makes an adaptation truly adaptive (that is, it improves an individual’s ability to survive and reproduce) is often dependent on context.242
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14
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Since adaptations are, by definition, features that help you have more offspring than others in your population, it follows that selection for adaptations will be most potent when the number of surviving descendants you have is most likely to vary. Put crudely, adaptations evolve most strongly when the going gets tough.255
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15
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Natural selection constantly pushes organisms toward optimality, but optimality is almost always impossible to achieve. Perfection may be unattainable, but bodies function remarkably well under a wide range of circumstances because of the way evolution accumulates adaptations in bodies270
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16
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adaptations evolve to promote health, longevity, and happiness only insofar as these qualities benefit an individual’s ability to have more surviving offspring.284
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The bottom line is that many human adaptations did not necessarily evolve to promote physical or mental well-being.288
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18
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Theodosius Dobzhansky, who famously wrote, “Nothing in biology makes sense except in the light of evolution.”329
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19
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life is most essentially the process by which living things use energy to make more living things.330
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20
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the story of the human body can be boiled down to five major transformations.368
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21
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TRANSITION ONE: The very earliest human ancestors diverged from the apes and evolved to be upright bipeds.
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TRANSITION TWO: The descendants of these first ancestors, the australopiths, evolved adaptations to forage for and eat a wide range of foods other than mostly fruit.
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TRANSITION THREE: About 2 million years ago, the earliest members of the human genus evolved nearly (though not completely) modern human bodies and slightly bigger brains that enabled them to become the first hunter-gatherers.
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TRANSITION FOUR: As archaic human hunter-gatherers flourished and spread across much of the Old World, they evolved even bigger brains and larger, more slowly growing bodies.
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TRANSITION FIVE: Modern humans evolved special capacities for language, culture, and cooperation that allowed us to disperse rapidly across the globe and to become the sole surviving species of human on the planet.370
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evolution (which I prefer to define as change over time)384
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Culture is essentially what people learn, and so cultures evolve. Yet a crucial difference between cultural and biological evolution is that culture doesn’t change solely through chance but also through intention, and the source of this change can come from anyone, not just your parents.390
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Looking back on the last few hundred generations, two cultural transformations have been of vital importance to the human body and need to be added to the list of evolutionary transformations above:
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TRANSITION SIX: The Agricultural Revolution, when people started to farm their food instead of hunt and gather.
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TRANSITION SEVEN: The Industrial Revolution, which started as we began to use machines to replace human work.394
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cultural evolution is now the dominant force of evolutionary change acting on the human body,409
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First, we get sick from noninfectious mismatch diseases caused by our bodies being poorly or inadequately adapted to the novel environments we have created through culture.412
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we don’t pass on mismatch diseases directly to our children. Instead it is a form of cultural evolution because we pass on the environments and behaviors that cause them.418
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If there was any one key initial adaptation, a spark that set the human lineage off on a separate evolutionary path from the other apes, it was likely bipedalism, the ability to stand and walk on two feet.454
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the last common ancestor (LCA) of humans and the other apes. To our great frustration, this important species so far remains entirely unknown.480
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humans are a special subset of the ape family termed hominins, defined as all species more closely related to living humans than to chimpanzees or other apes.491
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the counterintuitive fact that we are evolutionary first cousins with chimps but not gorillas provides valuable clues for reconstructing the LCA,499
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gorillas and chimps walk and run in the same peculiar fashion known as knuckle walking, in which they rest their forelimbs on the middle digits of the hand.504
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Animals move about for many reasons, including to escape predators and to fight, but a principal reason to walk or run is to get dinner.640
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we can conjecture with some confidence that the first hominins probably gorged as much as they could on fruit, but natural selection favored those better able to resort to eating less desirable, tough, fibrous foods, like the woody stems of plants, which require lots of hard chewing to break down.655
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regularly standing and walking upright was initially selected to help the first hominins forage and obtain food more effectively in the face of major climate change that was occurring when the human and chimpanzee lineages diverged.666
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If, as we think, the LCA was a mostly fruit-eating ape that lived in a rain forest, then natural selection would have favored the two major transformations we see in very early hominins such as Toumaï and Ardi.684
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Being able to walk farther using the same amount of energy would have been a very beneficial adaptation713
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bipedalism initially evolved because of an improbable series of events, all of which were contingent on earlier circumstances that were driven by chance shifts in the world’s climate.739
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Darwin’s successors to argue that it was big brains rather than bipedalism that led the way in human evolution.755
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probably became upright in order to forage more efficiently and to reduce the cost of walking758
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the first hominins must have had a slight reproductive advantage from being just partly better at standing or walking upright.769
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natural selection helped hominin mothers cope with this extra load by increasing the number of wedged vertebrae over which females arch their lower spines: three in females versus two in males.784
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How the Australopiths Partly Weaned Us Off Fruit805
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If you added up the amount of time you actually spent chewing, it would total less than half an hour per day. This is odd for an ape. Every day, from dawn to dusk, a chimpanzee spends nearly half its wakeful hours chewing like a raw foodist.808
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Were it not for the australopiths, your body would be very different, and you would probably be spending much more time in trees, mostly gorging on fruit.825
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Lucy, for example, was just under 65 pounds846
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Au. boisei, Au. robustus, and Au. aethiopicus. Put crudely, these robust species are the hominin equivalent of cows.865
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“What’s for dinner?” we have an unprecedented choice of abundant, nutritious foods available to us. Like other animals, however, our australopith ancestors ate only what they could find, not in fruit-filled forests as their predecessors enjoyed, but in more open habitats with fewer trees.885
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Humans still have to eat fallback foods on rare occasions. Acorns were a common food of last resort throughout Europe during the Middle Ages, and many Dutch people resorted to eating tulip bulbs to avoid starvation during the severe winter famine of 1944.893
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underground storage organs, or USOs.915
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If chimp fruits came with nutritional labels, you’d find that they are extremely high in fiber, but they are also moderately rich in starch and protein and low in fat.924
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if there is any one defining characteristic of the australopiths it is big, flat cheek teeth with thick enamel.953
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Basically, the australopiths, especially the robust species, had giant teeth shaped like millstones, well adapted for endlessly grinding and pulverizing tough food under high pressure.965
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In addition to being large, australopith chewing muscles were also configured to generate forces efficiently.986
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the robust australopiths have faces and jaws so heavily built they resemble armored tanks.995
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australopiths, like chimps and gorillas, probably loved fruit, but they must have eaten whatever foods they could get their hands on.996
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Switching from a diet primarily of fruit to one chiefly of tubers and other fallback foods must have had an enormous impact on australopith travel needs.1010
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Experiments that measure the energy cost of walking show that a bent-hip and bent-knee gait is considerably less efficient than walking normally: a male chimp that weighs 45 kilograms (100 pounds) spends about 140 calories to walk 3 kilometers (nearly 2 miles), around three times as much as a 65 kilogram (145 pound) human requires to walk the same distance.1037
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if the australopiths had to travel long distances regularly in search of fruit or tubers, increased economy of locomotion would have been very advantageous.1083
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The final major advantage of being a biped, emphasized by Darwin, was that it freed the hands for other tasks,1094
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you are not an australopith. Compared to Lucy and her kin, your brain is three times bigger, and you have long legs, short arms, and no snout. Instead of eating lots of low-quality food, you rely on very high quality food like meat, as well as tools, cooking, language, and culture. These and many other important differences evolved during the Ice Age, which began around two and a half million years ago.1116
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Getting dinner (or, for that matter, breakfast and lunch) probably does not dominate your list of daily concerns, yet most creatures are almost always hungry and preoccupied with the quest for calories and nutrients.1129
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More than anything else, the evolution of hunting and gathering spurred your body to be the way it is.1160
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According to the best evidence currently available, H. erectus first evolved in Africa by 1.9 million years ago and then rapidly started to disperse from Africa into the rest of the Old World.1171
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If you met a group of H. erectus on the street, you’d probably recognize them as being extremely humanlike, especially from the neck down.1179
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H. erectus was the first ancestor we can characterize as significantly human.1207
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Another highly valued food that hunter-gatherers extract is honey, which is sweet, tasty, and rich in calories but difficult and sometimes dangerous to acquire.1227
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If you add it all up, she probably needed about 3,000 to 4,500 calories on a typical day. Yet studies of contemporary hunter-gatherers in Africa show that mothers are able to gather between 1,700 and 4,000 calories of plant food per day, with nursing mothers encumbered by toddlers being at the lower end of that range.1235
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meat constitutes approximately one-third of the diet among hunter-gatherers in the tropics1244
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Although males hunted and scavenged, it is unlikely that early Homo mothers who were pregnant or nursing were able to hunt or scavenge on a regular basis, especially while taking care of toddlers. We can therefore infer that the origins of meat eating coincided with a division of labor in which females mostly gathered while males not just gathered but also hunted and scavenged.1251
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The first hunter-gatherers would have benefited so strongly from sharing food that it is hard to imagine how they could have survived without both females and males provisioning each other and cooperating in other ways.1261
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Food sharing, moreover, does not occur just between mates and between parents and offspring, but also between members of a group, highlighting the importance of intense social cooperation among hunter-gatherers. One basic form of cooperation is the extended family.1263
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it has been argued that grandmothers are so important that human females were selected to live long past the age they can be mothers so they can help provision their daughters and grandchildren.1266
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hunter-gatherers are highly egalitarian and they place great stock in reciprocity, helping assure everyone a more regular supply of resources.1275
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Group cooperation has probably been fundamental to the hunter-gatherer way of life for more than 2 million years.1277
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the human genus solved the problem of “what’s for dinner?” during a period of major climate change by adopting a radical, novel strategy. Instead of eating more low-quality food, these progenitors figured out how to procure, process, and eat more high-quality food by becoming hunter-gatherers. This way of life involves traveling long distances every day to forage for food and sometimes to scavenge or hunt. Hunting and gathering also requires intensive levels of cooperation and simple technology.1302
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Apes typically walk less than 3 kilometers (2 miles) a day, but hu-mans are prodigious long-distance walkers. One extreme human, George Meegan, recently trudged all the way from the southern tip of South America to the northernmost part of Alaska, averaging 13 kilometers (8 miles) a day.1318
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the ability to walk long distances during the day without overheating was probably a critical adaptation for early hunter-gatherers in Africa, allowing them to forage when carnivores were least likely to kill them.1355
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Standing and walking upright greatly decreases how much of the body’s surface gets maximally exposed to direct solar radiation, lessening how much the sun heats us up.1359
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humans, even amateur athletes, are among the best long-distance runners in the mammalian world.1387
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Today, humans run long distances to stay fit, commute, or just have fun, but the struggle to get meat underlies the origins of endurance running.1387
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even though zebras and wildebeest can gallop much faster than any sprinting human, we can hunt and kill these swifter creatures by forcing them to gallop in the heat for a long period of time, eventually causing them to overheat and collapse. This is just what persistence hunters do.1416
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No other mammal can do that because they lack sweat glands, and because most mammals are covered with fur. Fur is useful to reflect solar radiation, as a hat does, to protect the skin, and to attract mates, yet fur keeps air from circulating close to the skin, preventing sweat from evaporating. Humans actually have the same density of hairs as a chimpanzee, but most human hair is very fine, like peach fuzz.1438
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the gluteus maximus, the largest muscle in the human body. This enormous muscle is barely active during walking but contracts very forcefully during running to prevent the trunk from toppling forward with every step.1469
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Only humans can do this. Chimps and other primates sometimes toss rocks, branches, and nasty stuff like feces with reasonable aim, but they cannot throw anything with a combination of speed and accuracy. Instead, they hurl clumsily with a straight elbow,1528
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We are the only snoutless primates, in part thanks to tools.1551
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Most often you think with your brain, but sometimes the digestive system seems to take over and makes decisions on behalf of the rest of the body. Gut instincts are actually more than just urges or intuitions, and they highlight vital links between the brain and the gut that changed critically in the genus Homo following the origins of hunting and gathering.1553
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brains and guts each consume about the same amount of energy per unit mass, each expend about 15 percent of the body’s basal metabolic cost, and each requires similar amounts of blood supply to deliver oxygen and fuel and to remove wastes.1557
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Your guts also have about 100 million nerves, more than the number of nerves in your spinal cord or your entire peripheral nervous system.1560
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humans have relatively small guts and big brains.1565
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Effective hunting and gathering requires intense cooperation through sharing food and information and other resources. Further, cooperation among hunter-gatherers occurs not just among kin but also among unrelated members of the same group.67 Everyone helps everybody.1576
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Since these hunter-gatherers did not live in towns or cities, the only way a population could grow while staying at an appropriately low density would be for overly populous groups to split and disperse into new territories.1669
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Cooking, when it did catch on, was a transformative advance. For one, cooked food yields much more energy than uncooked food and is less likely to make you sick.1761
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in the 1950s, many paleontologists classified Neanderthals as a human subspecies (a geographically isolated race) rather than as a separate species. Recent data, however, show that Neanderthals and modern humans were indeed separate species that diverged genetically at least 800,000 to 400,000 years ago.21 Although there was a modicum of interbreeding between the two species, they are really close cousins, not ancestors.1778
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when modern humans did arrive in Europe starting about 40,000 years ago, they mostly replaced the Neanderthals.1799
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brain size nearly doubled in the human genus over the Ice Age, and species such as the Neanderthals had brains that were actually slightly larger than the average brain size of people today.1802
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This relationship between brain and body size turns out to be highly correlated and consistent. Therefore, if you know a species’ average body mass, you can compute its relative brain size by dividing its actual brain size by the size you would predict from its body mass. This ratio, known as the encephalization quotient (EQ), is 2.1 for chimps and 5.1 for humans.1814
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After accounting for slight differences in body weight, an average modern human is just a tiny bit brainier than an average Neanderthal.1832
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If bigger brains make you smarter, then Neanderthals and other big-brained archaic humans were pretty intelligent.1846
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Even though your brain constitutes only 2 percent of your body’s weight, it consumes about 20 to 25 percent of your body’s resting energy budget, regardless of whether you are sleeping, watching TV, or puzzling over this sentence.1847
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In absolute numbers, your brain costs 280 to 420 calories per day, whereas a chimpanzee’s brain costs about 100 to 120 calories per day.1849
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If you add up all the costs, it’s no wonder that most animals don’t have very large brains. Big brains may make you smarter, but they cost a lot and cause many problems.1867
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The biggest benefits of bigger brains were probably for behaviors we cannot detect in the archaeological record. One set of added skills must have been an enhanced ability to cooperate. Humans are unusually good at working together:1870
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apparent benefits of bigger brains is to help humans interact cooperatively with one another, often in large groups.1878
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Robin Dunbar showed that the size of the neocortex among primate species correlates reasonably well with group size.37 If this relationship holds true for humans, then our brains evolved to cope with social networks of about 100 to 230 people, which is not a bad estimate of how many people a typical Paleolithic hunter-gatherer might have encountered in a lifetime.1879
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The skills used to track an animal may underlie the origins of scientific thinking.1890
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Whatever the initial advantages of big brains, they must have been worth the cost or they wouldn’t have evolved.1891
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we can thank archaic Homo for the fact that we spend so much extra time and energy growing up.1901
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Adolescence is essentially that awkward, usually infertile period between the start of puberty and the end of skeletal growth, when reproductive maturity occurs.1908
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FIGURE 13. Different life histories. Humans have a more prolonged life history with an added stage of childhood and a longer period of being a juvenile prior to adulthood. Australopiths and early Homo erectus had a generally chimplike life history. Life history probably slowed down in species of archaic Homo, but exactly when and how much is still unclear.1922
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infer that early H. erectus matured only slightly slower than chimps, which means that prolonged juvenile and adolescent periods developed more recently in human evolution.1956
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Although fat and weight have probably obsessed humans for millions of years, until recently our ancestors mostly obsessed about not having enough fat in their diets and insufficient weight on their bodies. Fat is the most efficient way of storing energy, and at some point our ancestors evolved several key adaptations for amassing larger quantities of fat than other primates.1978
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All animals need fat, but humans have a special need for lots of fat right from the moment of birth, largely because of our energy-hungry brains. An infant’s brain is a quarter the size of an adult’s, but it still consumes about 100 calories per day, about 60 percent of the tiny body’s resting energy budget (an adult’s brain consumes between 280 and 420 calories per day, 20 to 30 percent of the body’s energy budget).1990
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(your total energy expenditure, TEE) versus how much energy you acquire (your daily energy production, DEP).2032
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once you take care of your body’s basic needs, you can spend surplus energy in four different ways. You can use it to grow if you are young, you can store it as fat, you can be more active, or you can spend it on having and raising more offspring.2057
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the most illustrative example of how our dependence on energy can backfire is the case of Homo floresiensis, otherwise known as the Hobbit, a dwarfed species of archaic humans from Indonesia.2079
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in 2003, a team of Australian and Indonesian researchers digging in the cave of Liang Bua made headlines around the world when they found a partial skeleton of a tiny fossil human dated to between 95,000 and 17,000 years ago. They named it H. floresiensis and proposed that it was the remnant of a dwarfed species of early Homo.64 The media quickly nicknamed the species the Hobbit.2097
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H. erectus got to the island at least 800,000 years ago and was driven by natural selection to become small-brained and small-statured in order to cope with a lack of food.2105
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Culture is roughly anything we do and the monkeys don’t. —FITZROY SOMERSET (LORD RAGLAN)2148
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Tasaday had no words for violence or war. If only more people were like the Tasaday… Unfortunately, the Tasaday were a hoax. The tribe’s existence was apparently staged by its “discoverer,” Manuel Elizalde, who is alleged to have paid a handful of nearby villagers to swap their jeans and T-shirts for orchid leaf loincloths and to eat bugs and frogs instead of rice and pork for the TV cameras.2154
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what is most profoundly different about modern humans compared to archaic humans is our capacity for cultural change. We have a unique and totally unprecedented ability to innovate and transmit information and ideas from person to person.2186
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the best answer to the question of what makes Homo sapiens special and why we are the only human species alive is that we evolved a few slight changes in our hardware that helped ignite a software revolution that is still ongoing at an escalating pace.2191
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modern humans evolved from archaic humans in Africa at least 200,000 years ago.2198
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all living humans can trace their roots to a common ancestral population that lived in Africa about 300,000 to 200,000 years ago, and that a subset of humans dispersed out of Africa starting about 100,000 to 80,000 years ago.2201
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all human beings were Africans. These studies also reveal that all living humans are descended from an alarmingly small number of ancestors. According to one calculation, everyone alive today descends from a population of fewer than 14,000 breeding individuals from sub-Saharan Africa, and the initial population that gave rise to all non-Africans was probably fewer than 3,000 people.2204
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human and Neanderthal DNA are extremely similar:2218
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although the Neanderthals are extinct, a little bit of them lives on in me.2229
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evidence suggests that as modern humans spread rapidly throughout Europe, Neanderthal populations dwindled2245
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it is unclear why only modern humans have chins,2275
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the first modern humans who inhabited Africa at this time were trading over long distances, suggesting large and complex social networks.2292
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Evidence for symbolic behavior among Neanderthals is exceedingly rare.2296
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starting about 50,000 years ago, something extraordinary happened: Upper Paleolithic culture was invented.2301
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the most profound transformation evident in the Upper Paleolithic revolution is cultural: people were somehow thinking and behaving differently. The most tangible manifestation of this change is art.2318
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if there is anything most different about modern humans compared to our archaic cousins it is our remarkable capacity and proclivity to innovate through culture.2328
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Hundreds of archaeological sites testify that the Neanderthals lacked modern humans’ tendencies to invent new tools, adopt new behaviors, and express themselves as much using art. Was this lack of cultural flexibility and inventiveness the reason we survived and they went extinct? Or did we simply outbreed them?2332
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Brains don’t fossilize, and we have yet to find a frozen Neanderthal deep within a glacier.2337
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most obvious and significant difference in the neocortex of modern and archaic humans is that the temporal lobes are about 20 percent bigger in just H. sapiens.2356
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reasonable to hypothesize that enlarged temporal lobes may help modern humans excel at language and memory.2361
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Brain surgeons have discovered that stimulating the temporal lobe during surgery in alert patients can elicit intensely spiritual emotions even in self-described atheists.2363
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Another part of the human brain that appears to be relatively bigger in modern humans is the parietal lobes.35 This pair of lobes plays key roles in interpreting and integrating sensory information from different parts of the body.2364
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the prefrontal cortex helps you to cooperate and behave strategically.2378
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rounder brains not only helped us look more modern, they also helped us behave more modernly.2395
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My guess is that Neanderthals were extremely smart, but that modern humans are more creative and communicative.2417
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Neanderthals surely had language, the uniquely short and retracted face of modern humans would have made us better at uttering clear, easy-to-interpret speech sounds at a very rapid rate. We are a uniquely silver-tongued species.2422
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the human configuration allows you to be a little sloppy when speaking yet still produce discrete vowels that your listener will recognize correctly without having to rely on context.2454
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By dropping the larynx low in the neck, humans lost the tube within a tube and developed a big common space behind the tongue through which food and air both travel to get into either the esophagus or the trachea. As a result, food sometimes gets lodged in the back of the throat, blocking off the airway.2463
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Humans are the only species that risks asphyxiation when we swallow something too large or imprecisely. This cause of death is more common than you may think. According to the National Safety Council, choking on food is the fourth leading cause of accidental deaths in the United States, approximately one-tenth the number of deaths caused by motor vehicles. We have paid a heavy price for speaking more clearly.2465
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Next time you have a meal and chat with friends, consider that you are probably doing two unique things: speaking with great clarity and swallowing a little dangerously.2468
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once the Upper Paleolithic was in full force, it helped modern humans spread rapidly around the globe, and our archaic cousins vanished whenever and wherever we arrived.2474
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Many theories exist. One possibility is that we simply outbred them, perhaps by weaning our children younger or having lower mortality rates.2477
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Other, nonexclusive hypotheses are that modern humans outcompeted our cousins because we were better at cooperating, that we foraged and hunted for a wider range of resources, including more fish and fowl, and that we had larger, more effective social networks.2483
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Culture is a term with multiple meanings, but it is most essentially a set of learned knowledge, beliefs, and values that cause groups to think and behave differently,2490
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the archaeological record associated with modern humans indicates unambiguously that we have an extraordinary and special capacity and proclivity to innovate and to transmit new ideas. H. sapiens is a fundamentally and exuberantly cultural species.2493
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cultural traits, known as “memes,” differ from genes in several key respects.56 Whereas new genes arise solely by chance through random mutations, humans often generate cultural variations intentionally.2500
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these differences make cultural evolution a faster and often more potent cause of change than biological evolution.57 Culture itself is not a biological trait, but the capacities that enable humans to behave culturally, and to use and modify culture, are basic biological adaptations that appear to be specially derived in modern humans.2506
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The most basic interactions between culture and your body’s biology are the ways that learned behaviors—the foods you eat, the clothes you wear, the activities you do—alter your body’s environment, thus influencing how your body grows and functions. The effects don’t cause evolution per se (that would be Lamarckian), but over time some of these interactions do make possible evolutionary change in populations.
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Sometimes cultural innovations drive natural selection on the body. A beautifully studied example is the ability to digest milk sugar as an adult (lactase persistence), which evolved independently in Africa, the Middle East, and Europe among peoples who consumed animal milk.2512
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there was strong selection for dark pigmentation near the equator, where ultraviolet radiation is intense year-round, but populations who moved into temperate zones were selected to have less pigmentation to ensure sufficient levels of vitamin D.2551
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if there is any special adaptation of modern humans that accounts for our evolutionary success (so far) it must be our ability to be adaptable because of our extraordinary capacities to communicate, cooperate, think, and invent.2559
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of all the qualities that make modern humans special, our cultural abilities have been the most transformative and the most responsible for our success.2568
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human evolution appears to be, first and foremost, a triumph of brains over brawn.2573
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I think it is not just incorrect but also dangerous to view modern human evolution as solely a triumph of brains over brawn.2581
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As modern hunter-gatherers colonized the planet, they invented a stunning array of technologies and strategies to cope with diverse new conditions.2602
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In truth, there is no single hunter-gatherer diet, just as there was no one system of kinship or religion, no one mobility strategy, division of labor, or group size.2609
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Farming has been around for just a few hundred generations,2617
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Thoreau’s hut was a several-mile walk from the center of Concord, Massachusetts,2634
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Almost every major infectious epidemic, such as smallpox, polio, and the plague, happened after the Agricultural Revolution began.2655
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the human species has achieved considerable progress over the last few thousand years since we ceased to be hunter-gatherers, but how and why has some of this progress been bad for our bodies?2673
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the Agricultural Revolution has been an especially powerful force for evolutionary change.2691
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although natural selection has not ceased to act, we know that it has had only limited, regional effects on human biology over the last few thousand years.2721
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If you were to raise a Cro-Magnon girl from the Upper Paleolithic in a modern French household, she would still be a typical modern human girl except for some modest biological differences, probably mostly in her immune system and her metabolism.2722
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As cultural evolution is accelerating, environmental changes that affect how our bodies grow and function are also accelerating.2739
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not all evolution occurs through natural selection, and interactions between genes and the environment have been changing rapidly, sometimes radically, primarily because of changes in our bodies’ environments caused by rapid cultural evolution.2752
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knowing your body’s evolutionary history helps to evaluate why your body looks and works as it does, hence why you get sick.2773
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cancerous cells are nothing more than abnormal cells with mutations that enable them to survive and reproduce better than other cells. If we hadn’t evolved to evolve, we would never get cancer.2781
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Overusing antibiotics not only promotes the evolution of novel superbugs but also alters the body’s ecology in ways that may contribute to new autoimmune illnesses, such as Crohn’s disease2789
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sometimes get sick because natural selection generally favors fertility over health, meaning we didn’t necessarily evolve to be healthy.2803
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These illnesses are mismatch diseases, defined as diseases that result from our Paleolithic bodies being poorly or inadequately adapted to certain modern behaviors and conditions.2823
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You are most likely going to die from a mis-match disease. You are most likely to suffer from disabilities caused by mismatch diseases. Mismatch diseases contribute to the bulk of health-care spending throughout the world.2825
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everyone in every generation inherits thousands of genes that interact with his or her environment, and most of these genes were selected over the previous few hundreds, thousands, or even millions of generations because they improved their ancestors’ ability to survive and reproduce under certain environmental conditions. Therefore, thanks to the genes you inherited, you are adapted to varying extents for certain activities, foods, climatic conditions, and other aspects of your environment. At the same time, because of changes to your environment, you are sometimes (but not always) inadequately or poorly adapted for other activities, foods, climatic conditions, and so on. These maladaptive responses can sometimes (but again, not always) make you sick.2830
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mismatch diseases occur when a common stimulus either increases or decreases beyond levels for which the body is adapted, or when the stimulus is entirely novel and the body is not adapted for it at all. Put simply, mismatches are caused by stimuli that are too much, too little, or too new.2845
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is that there is no straightforward answer to what humans are adapted for.2873
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absence of evidence isn’t always evidence of absence.2898
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TABLE 3. Hypothesized Noninfectious Mismatch Diseases2910
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cavities are the price we pay for cheap calories.2952
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In the case of cavities, I didn’t pass on my cavities to my daughter, but I did pass on a diet that causes them, and she is likely to do the same to her children.2959
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“palliative” (first used in the fifteenth century) was to refer to care that “relieves the symptoms of a disease or condition without dealing with the underlying cause.”2962
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we lack a good term for the deleterious feedback loop that occurs over multiple generations when we don’t treat the causes of a mismatch disease but instead pass on whatever environmental factors cause the disease, keeping the disease prevalent and sometimes making it worse. I am generally averse to neologisms, but I think “dysevolution” is a useful and fitting new word because, from the body’s perspective, the process is a harmful (dys) form of change over time (evolution).2967
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When you have a cold, you don’t complain about the viruses in your nose and throat, you complain about the fever, cough, and sore throat that make you miserable.2988
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sometimes so effective at treating a mismatch disease’s symptoms that we reduce the urgency of treating its causes. I suspect this is the case for cavities,2993
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A second characteristic of dysevolution is that one expects the process to apply mostly to mismatch diseases that have a low or negligible effect on reproductive fitness.3005
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The hypothesis of dysevolution predicts that as long as we accept or cope with the symptoms of the problems these products create, often thanks to other products, and as long as the benefits exceed the costs, then we will continue to buy and use them and pass them on to our children, keeping the cycle going long after we are gone.3018
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According to Jared Diamond, farming was the “worst mistake in the history of the human race.”1 In spite of having more food, hence more children, than hunter-gatherers, farmers generally have to work harder; they eat a lower-quality diet; they more often confront starvation because their crops occasionally fail from floods, droughts, and other disasters; and they live at higher population densities, which promote infectious diseases and social stress. Farming may have led to civilization and other types of “progress,” but it also led to misery and death on a grand scale. Most of the mismatch diseases from which we currently suffer stem from the transition from hunting and gathering to farming.3052
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A far more important factor that spurred on the origin of farming in different parts of the globe was population stress.3072
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But then crisis struck 12,800 years ago. All of a sudden, the world’s climate deteriorated abruptly, perhaps because an enormous glacial lake in North America emptied suddenly into the Atlantic, temporarily disrupting the Gulf Stream and wreaking havoc with global weather patterns.8 This event, called the Younger Dryas,9 effectively plunged the world back into Ice Age conditions for hundreds of years.3114
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Man’s best friend, the dog, was actually the first domesticated species. We bred dogs from wolves more than 12,000 years ago, but there is much debate over when, where, and how this domestication occurred (and to what extent dogs actually domesticated us).3150
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regardless of how farming originated, it then spread like contagion. A major reason for this rapid spread was population growth.3154
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the rate of population growth fluctuated after farming began, and was sometimes even higher, but there is no question that it launched the first major population explosion in human history.3165
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farming did begin to generate a series of mismatch diseases and other problems because millions of years of adaptations for Paleolithic life did not fully prepare the human body to be farmers.3202
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the first farmers could double their family size.3223
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blight, a funguslike microorganism, spread throughout the potato fields in 1845, wiping out more than 75 percent of the harvest for four years in a row and causing more than a million deaths.3253
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a hunter-gatherer’s chances of dying from starvation must be orders of magnitude lower than any farmer’s.3258
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After a meal, starches and sugars stick to your teeth and attract bacteria that multiply and combine with proteins in your mouth to form plaque, a whitish film surrounding the tooth. As the bacteria digest sugars they excrete acid, which is trapped by the plaque and then dissolves the enamel crown, causing cavities. Cavities are rare among hunter-gatherers but extremely common in early farmers.3275
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Farmers—even Neolithic pioneers who lacked fertilizers, irrigation, and plows—can grow much more food than hunter-gatherers can acquire, but a farmer’s diet is generally less healthy and more risky.
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Farmers consume foods that are starchier and contain less fiber, less protein, and fewer vitamins and minerals. Farmers are also more susceptible to eating contaminated food, and they risk famine more regularly and intensely than hunter-gatherers. In terms of diet, humans have paid a high price for the pleasure of enjoying a yearly harvest feast.3297
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Although hunting and gathering is not easy, nonfarming populations like the Bushmen or the Hadza generally work only five to six hours a day.3303
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Farming involves endless physical toil, sometimes from dawn to dusk.3310
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One very simple way to compare the workloads of farmers, hunter-gatherers, and modern postindustrial people is to measure physical activity levels (PALs).3315
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A PAL score measures the number of calories spent per day (total energy expenditure) divided by the minimum number of calories necessary for the body to function (the basal metabolic rate, BMR). In practical terms, a PAL is the ratio of how much energy one spends relative to how much one would need to sleep all day at a comfortable temperature of about 25 degrees Celsius (78 degrees Fahrenheit).3316
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Evidence that subsistence farming involves amounts of overall physical labor similar to or slightly higher than hunting and gathering should not be surprising if one considers the kinds of physical activities that farmers did before the invention of mechanized machines such as tractors.3326
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child labor has an ancient agricultural history because children are needed for their substantial contributions to a family’s economic success, especially on a farm.3335
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Of all the advantages of farming, the most fundamental and consequential is that more calories allow people to have bigger families, leading to population growth.3338
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One prerequisite of plagues is large populations, which didn’t happen until farming.3342
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Another prerequisite of plagues are permanent settlements with high population densities.3357
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Living in larger, denser communities is socially stimulating and economically profitable, but such communities also pose life-threatening health hazards.3366
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By aggregating many potential hosts in close contact with one another, villages and towns become ideal places for infectious diseases to thrive,3370
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epidemics could not exist prior to the Neolithic because hunter-gatherer population densities are below one person per square kilometer, which is beneath the threshold necessary for virulent diseases to spread.3379
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All told, there are probably more than one hundred infectious mismatch diseases that were caused or exacerbated by the origin of agriculture. Fortunately, in the last few generations modern medicine and public health have made great strides in preventing and combating many of these diseases.3419
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Farming not only allowed people to have bigger families but also to settle down in villages, towns, and cities, causing a massive, still ongoing shift in human settlement patterns. Farming was also a precursor to surpluses, which made possible art, literature, science, and many other human achievements. In effect, farming made civilization possible.
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The other side of the coin, however, is that farming surpluses also made possible social stratification, hence oppression, slavery, war, famine, and other evils unknown to hunter-gatherer societies.
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Farming also ushered in many mismatch diseases that range from cavities to cholera. Hundreds of millions of people have died from plagues, malnutrition, and starvation—deaths that would not have occurred had we remained hunter-gatherers. Yet, despite these many deaths, there are nearly six billion more people alive today than would be the case had the Agricultural Revolution never begun.
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Although farming has been a boon for the human species as a whole, it was a mixed blessing to the human body.3432
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With few exceptions, people shrank as agricultural economies intensified.3456
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the unfortunate irony of agricultural intensification is that even though farmers produced more food overall, the energy available for each child to grow diminished, probably because they were spending relatively more energy fighting infections, coping with occasional shortages of food, and toiling long hours in the fields.3460
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Other types of data confirm that the transition to farming generally challenged people’s health.3462
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Simply put, over time, farming life generally became nastier, more brutish, shorter, and more painful.3468
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Milk contains a special form of sugar, lactose, which is broken down by the enzyme lactase. Preagricultural humans never had to digest milk after they stopped nursing, and as most humans mature, their digestive system naturally stops producing lactase by the time they are five or six years old.3502
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recent genetic adaptations that have evolved independently in different parts of the New and Old Worlds are modest compared to the scale and degree of cultural innovation that humans have cooked up over the same time frame.3514
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Many of these cultural innovations—the wheel, plows, tractors, writing—have improved economic productivity, but quite a few were responses to mismatch diseases caused by the farming way of life. Stated more precisely, many of these innovations have acted as cultural buffers that have insulated or even protected farmers from the dangers and drawbacks of agriculture, which would otherwise have resulted in even stronger selection than we can detect.3515
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Children born today are far less likely to die from infectious mismatch diseases caused by the Agricultural Revolution and they are much more likely to live longer, grow taller, and be generally healthier than children born in my grandfather’s generation.3572
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on the other hand, our bodies face new problems that were barely on anyone’s radar screen a few generations ago. People today are much more likely to get sick from new mismatch diseases such as type 2 diabetes, heart disease, osteoporosis, and colon cancer, which were either absent or much less common for most of human evolutionary history, including most of the agricultural era.3575
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We have even industrialized exercise: more people get pleasure from watching professional athletes compete in televised sports than by participating in sports themselves.3602
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Regardless of whether you think the industrial era has been good or bad, three profoundly fundamental shifts underlie this revolution. The first is that industrialists harnessed new sources of energy, primarily to produce things.3606
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A second major component of the Industrial Revolution was a reorganization of economies and social institutions.3613
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Finally, the Industrial Revolution coincided with a transformation of science from a pleasant but nonessential branch of philosophy into a vibrant profession that helped people make money.3623
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In short, the Industrial Revolution was actually a combination of technological, economic, scientific, and social transformations that rapidly and radically altered the course of history and reconfigured the face of the planet in less than ten generations—a true blink of an eye by the standards of evolutionary time. Over the same period, the Industrial Revolution also changed everyone’s bodies. It changed what we eat, how we chew, how we work, and how we walk and run, as well as how we keep cool and warm, give birth, get sick, mature, reproduce, grow old, and socialize.3631
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In a typical day, a receptionist or bank clerk who spends an eight-hour day seated in front of a computer expends about 775 calories while doing her job, a worker at an automobile factory spends about 1,400 calories, and a really hardworking coal miner could spend a whopping 3,400 calories.3663
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Nothing over the last few million years of human history has changed human energetics as much as the low cost of working at a desk using machines run by electric power.3677
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Less than 3 percent of shoppers in an American mall voluntarily take the stairs when an escalator is available to make their journey easier (the percentage doubles with signs that encourage stair use).3692
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Sugar has become so superabundant and so cheap that the average American consumes more than 100 pounds (45 kilograms) a year!3742
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If you were to walk into an American fast-food restaurant in 1955 and order a hamburger and fries, you’d consume about 412 calories, but today for the same price (in inflation-adjusted dollars) the same order would have double the amount of food, totaling 920 calories.3749
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Such foods (termed high glycemic foods) are quickly and easily broken down, but our digestive systems are not well adapted to the rapid swings in blood sugar levels they cause.3790
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In short, the invention of agriculture caused the human food supply to increase in quantity and deteriorate in quality, but food industrialization multiplied this effect.3800
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The number of lives that have been saved by penicillin is too great to count, but it must be in the hundreds of millions.3864
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A typical American spends an average of 7.5 hours in bed every night but sleeps for only 6.1 hours, 1 hour less than the national average from 1970, and between 2 and 3 hours less than 1900.40 In addition, only a third of Americans take naps.3921
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A typical Hadza hunter-gatherer wakes up every morning at dawn (always between 6:30 and 7:00 a.m. at the equator), enjoys a one- to two-hour nap at midday, and goes to bed around 9:00 p.m.42 People also didn’t usually sleep in a single bout but considered it normal to wake in the middle of the night before having a “second sleep.”3929
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During normal sleep, the body is at rest, causing levels of one hormone, leptin, to rise, and another hormone, ghrelin, to fall. Leptin suppresses appetite and ghrelin stimulates appetite, so this cycle helps you avoid getting hungry in your sleep.3957
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Was it worth it? From the perspective of the human body, the answer to this question must be “very much so—but not much at first.”3970
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the three most predictable consequences of the Industrial Revolution on the human body are bigger bodies, more babies, and greater longevity.3990
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In short, the combined effects of lower infant mortality, higher longevity, and increased fertility have fueled an explosion in the world’s population,4058
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the global growth rate peaked in 1963 at 2.2 percent per year and has since declined to about 1.1 percent per year,4062
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In the fifty years between 1960 and 2010, the world’s population more than doubled, from 3 to 6.9 billion people.4064
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In 1800, only 25 million people lived in cities, about 3 percent of the world’s population. In 2010, about 3.3 billion people, half the world’s population, are city dwellers.4070
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lower rates of mortality have been accompanied by higher rates of morbidity4083
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By the year 2015, there will be more people over the age of sixty-five than under the age of five, yet nearly half of those above the age of fifty will be in some state of pain, disability, or incapacity that requires medical care.4128
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Hunter-gatherers who survive childhood typically live to be old: their most common age of death is between sixty-eight and seventy-two,4144
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several studies consistently rank the following factors as especially important causes of morbidity among people in developed nations (in rough order): high blood pressure, tobacco smoking, overuse of alcohol, pollution, a diet low in fruit, high body-mass index, high fasting levels of blood glucose, physical inactivity, high sodium, diets low in nuts and seeds, and high cholesterol.4171
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none of these risk factors were common before the Agricultural and Industrial Revolutions.4177
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An evolutionary perspective confirms that humans are exquisitely adapted to gain weight and that storing a relatively large quantity of body fat is normal.4228
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Whenever you do anything, such as grow, walk, digest, sleep, or read these words, you spend energy. Almost all of the energy that your body uses to fuel activities is stored in a tiny ubiquitous molecule called ATP (adenosine triphosphate). ATPs are like minuscule batteries that circulate in your body’s cells, giving off energy when needed. In turn, your body synthesizes and recharges ATP molecules by burning fuels, mostly carbohydrates and fats. You eat not just to replenish these energy stores but also to create an energy reserve so you never run out of ATP, even for an instant. ATP thus functions in your body like money that you acquire, use, and save.4240
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A typical adult’s resting metabolism requires about 1,300 to 1,600 calories a day,4254
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breaking down the food into its basic components: proteins, carbohydrates, and fats. Proteins are coiled chains of amino acids; carbohydrates are long chains of sugar molecules; fats are made of three long molecules called fatty acids held together by a single colorless, odorless molecule known as glycerol4260
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There are many different kinds of sugars, but the two most common basic forms are glucose and fructose.4281
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Glucose, which is not very sweet, is the essential sugar that makes up starch, so all the flour from your cake is quickly broken down to glucose.4284
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Insulin has several other jobs, but its most critical function is to keep glucose levels from rising too high,4291
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The other kind of sugar in your cake is fructose, which tastes sweet. Fructose, which is often paired with glucose, is naturally present in fruit and honey, as well as table sugar (sucrose, which is 50 percent fructose).4298
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the bottom line is that your body functions like a fuel bank, storing energy after you eat food and withdrawing energy for use during times of need. This exchange, which is mediated by hormones, occurs through an endless flux of fat and carbohydrates to and from the liver, fat cells, muscles, and other organs.4311
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Humans, like other animals, are therefore marvelously adapted to remaining active even during long periods of negative energy balance.4313
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Other primates generally average about 6 percent body fat when they are adults, and their infants are born with about 3 percent body fat, but the percentage of body fat among human hunter-gatherers is typically 15 percent in newborns, rises to about 25 percent during childhood, and then falls to about 10 percent in males and about 20 percent in females.4339
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Hunter-gatherers thus profit immensely from having plentiful energy reserves to forage and feed their kids during inevitable times when they don’t have enough food to maintain a constant body weight. Having a few pounds of extra body fat can make the difference between life and death, strongly affecting reproductive success.4349
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Because women who have stored up more energy as fat are more likely to have more surviving offspring, natural selection favored 5 to 10 percent more body fat in women than men.13 The bottom line is that fat is vital for all species, but especially for humans.4358
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Genes do matter, but diet and physical activity are far more potent predictors of obesity and illness.4374
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famines became much more common and severe after farming began.4378
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the key point is that excessive weight gain relative to height during childhood is a strong risk factor for future diseases associated with metabolic syndrome.4407
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The “calories in versus calories out” explanation for the obesity epidemic is not entirely wrong, but the situation is more complicated because we have also changed what we are eating.4427
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when we compare the two apple products, the real apple not only supplies less sugar, but it makes you feel more sated and causes you to digest those sugars at a much more gradual rate. In contrast, the fruit rolls are termed high glycemic because they rapidly and markedly elevate blood sugar levels (a condition known as hyperglycemia).4450
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When you eat the apple, your insulin levels rise, but they rise gradually because the apple’s fiber slows the rate at which you extract the glucose. As a result, your body has plenty of time to figure out how much insulin to make to keep your blood glucose levels steady. In contrast, the fruit roll’s double load of glucose passes rapidly into your bloodstream, causing your blood sugar levels to skyrocket, in turn causing your pancreas to frantically pump out lots of insulin, often too much. This overshoot commonly causes your blood sugar levels to subsequently plummet, and you then become ravenous, causing you to crave more fruit rolls or other calorie-dense foods to raise your blood sugar quickly back to normal again.4454
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Put simply, foods rich in rapidly digested glucose supply lots of calories and make you hungrier sooner. People who eat meals with a higher percentage of calories from protein and fat are less hungry for longer and thus eat less food overall than people whose calories come mostly from sugary and starchy foods.4460
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Less processed food with more fiber also induces hunger less quickly because the food remains longer in the stomach, which releases appetite-suppressing hormones.4463
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Why is the fructose in raw fruit less likely to promote obesity than the fructose in the processed fruit or other fructose-laden foods like soda and fruit juice? The answer again has to do with the combination of the quantity and the rate at which the fructose is handled by the liver.4468
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almost all the fruits our ancestors ate were about as sweet as carrots—hardly4472
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If fructose sounds dangerous, it can be, but only in fast and large doses. For most of human evolution the only big, rapidly digestible source of fructose that our ancestors could acquire was honey.4482
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the chief reason why more people are getting fatter, especially in our bellies, is that processed foods are supplying them with too many calories, many from sugar—both glucose and fructose—in doses that are both too high and too rapid for the digestive systems we inherited.4487
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The most potent gene so far discovered, FTO, affects how the brain regulates appetite.4503
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for thousands of generations, almost all the people who carried these genes had normal body weights, emphasizing that what has most changed are environments, not genes. It follows that if we are to quell this epidemic, we need to focus not on genes but on environmental factors.4509
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Cortisol doesn’t make you stressed; it is released when you are stressed. Among its many functions, cortisol gives you needed, instant energy: it causes your liver and fat cells, especially visceral fat cells, to release glucose into the bloodstream, it increases your heart rate and increases your blood pressure, and it makes you more alert and inhibits sleep.4516
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Insufficient sleep also elevates levels of yet another hormone, ghrelin. This “hunger hormone” is produced by your stomach and pancreas and stimulates appetite.4532
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our evolutionary history did not adapt us well to cope with relentless, endless stress and sleep deprivation.4534
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Diabetes is actually a group of diseases, all of which are characterized by the inability to produce enough insulin.4569
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blood glucose levels rise as you digest a meal, providing fuel for your cells to burn.4596
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When obese adolescents with high levels of insulin resistance are enticed to exercise moderately (thirty minutes a day, four times a week, for twelve weeks), their insulin resistance decreases to nearly normal levels.53 Stated simply, increasing levels of physical activity and decreasing levels of visceral fat can reverse early type 2 diabetes.4634
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Many studies have consistently found that even moderate levels of physical activity such as walking fifteen miles a week substantially raises levels of HDLs and lowers levels of triglycerides in the blood—both of which lower the risk of heart disease.4727
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In general, the duration of activity appears to have more beneficial effects on these risk factors than the intensity of activity.4731
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The worst of all possible fats are unsaturated fats that have been industrially converted into saturated fats under high heat and pressure. These unnatural trans fats don’t go rancid (hence their use in many packaged foods), but they wreak havoc on the liver: they raise LDLs, lower HDLs, and interfere with how the body uses omega-3 fats.66 Trans fats are essentially a form of slow-acting poison.4753
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Although unsaturated fats are generally healthier than saturated ones, saturated fat may not be as evil as some think.4774
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salt—the only rock we eat.4784
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Moderate alcohol consumption lowers blood pressure and improves cholesterol ratios, but overconsumption damages the liver, which then ceases to function properly to regulate fat and glucose levels.4793
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All cancers, however, start from chance mutations in some errant cell.4820
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large-scale studies that showed that a woman’s chances of developing breast, ovarian, or uterine cancer increase significantly with the number of menstrual cycles she experiences and decrease with the number of children she bears.4842
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the more energy your body spends on physical activity the less it can spend on pumping out reproductive hormones. Women who are physically active have estrogen rates about 25 percent lower than those who are sedentary.91 These differences may partially account for why several studies have documented that just a few hours a week of moderate exercise substantially lowers the rates of many cancers,4881
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three characteristics of such mismatch diseases. First, they tend to be chronic, noninfectious diseases with multiple interacting causes that are difficult to treat or prevent. Second, these diseases tend to have a low or negligible effect on reproductive fitness. Third, the factors that contribute to these diseases have other cultural values, leading to trade-offs between their costs and benefits.4917
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About one-third of people who are overweight show no sign of metabolic disturbance, perhaps because they have genes that adapt them to being heavy.4950
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Even more important predictors of health and longevity are where you store your body fat, what you eat, and how physically active you are.4952
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One landmark study, which followed nearly 22,000 men of all weights, sizes, and ages for eight years, found that lean men who did not exercise had twice the risk of dying as obese men who engaged in regular physical activity4953
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diseases of disuse. These illnesses are caused by too little, rather than too much, of a good thing.4959
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Osteoporosis causes more than one-third of elderly women in the United States to fracture bones, but the disease was rare among the elderly until recently.4977
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As we age, the genes we inherited interact intensely and constantly with the environment to affect how our bodies grow and develop.4986
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Humans are born with millions of sweat glands, but the percentage of glands that actually secrete sweat when you get hot is influenced by how much heat stress you experienced in the first few years of life.5008
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The capacity for bodies to adjust their observable characteristics (their phenotype) in response to environmental stresses is formally known as phenotypic plasticity.5013
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By favoring mechanisms that adjust phenotypes to particular environments, natural selection helps bodies find the right balance between diverse tasks and attain the right level of function: enough but not too much.5027
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People who played lots of tennis as youngsters have bones in their dominant, racket-swinging arm that are up to 40 percent thicker and stronger than in their other arm.5062
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once the skeleton stops growing up, bones can no longer grow much thicker. If you start whacking lots of tennis balls as an adult, your arm bones might get a little thicker but not as much as a teenage tennis player’s would.5068
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your skeleton attains its peak size soon after you become an adult, between eighteen and twenty years in girls and between twenty and twenty-five years in boys.9 After then, there is little you can do to make your bones bigger, and soon thereafter your skeleton starts to lose bone for the rest of your life.5070
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osteoporosis afflicts at least a third of all women over the age of fifty and at least 10 percent of similarly aged men,5090
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Osteoporosis-related fractures, however, are exceedingly uncommon in the archaeological record, even after farming began.12 Instead, the evidence suggests that osteoporosis is a mostly modern mismatch disease caused by interactions between the genes you inherited and several risk factors: physical activity, age, sex, hormones, and diet.5094
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skeleton mostly forms before one’s early twenties, lots of weight-bearing activity during youth—especially during puberty—leads to greater peak bone mass.5127
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A body needs abundant calcium to function properly, and one of bone’s many jobs is to serve as a reservoir of this vital mineral.5135
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keep in mind that merely getting enough calcium and vitamin D is not enough to prevent or reverse the disease. You still need to load your skeleton to stimulate your osteoblasts to use that calcium.5143
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millions of years of natural selection did not gear our skeletons to mature in the absence of plentiful physical activity along with lots of calcium, vitamin D, and protein. Also, until recently, women did not go through puberty until they were sixteen, giving them several extra years to build a larger, stronger skeleton.5149
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impacted wisdom teeth are another example of an evolutionary mismatch.5174
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most of the hunter-gatherers had nearly perfect dental health.5178
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Just as your limbs and spine will not grow strong enough if you don’t sufficiently stress your bones by walking, running, and doing other activities, your jaws won’t grow large enough for your teeth and your teeth won’t fit properly if you don’t stress your face sufficiently from chewing food.5182
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a childhood spent chewing on hard, tough food helps your jaws grow big and strong.5191
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Tooth shape is mostly controlled by genes, but proper tooth position in the jaw is heavily influenced by chewing forces.5198
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If you don’t chew enough, your teeth are more likely to be misaligned.5200
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If you don’t chew forcefully enough when you are young, your teeth won’t be in the right position, and your jaws may not grow large enough to accommodate your wisdom teeth.5206
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Try eating like a caveman for a few days: eat only roasted game, roughly chopped vegetables, and nothing that has been ground, pureed, boiled, or softened using modern technologies. Your jaw muscles will fatigue because they are not used to working that hard.5214
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over the last few thousand years human faces have become about 5 to 10 percent smaller after correcting for body size, about the same size reduction we see in the faces of animals fed cooked, softened food.5219
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if we could reduce the incidence of orthodontic problems by encouraging children to chew more gum? Many grown-ups consider chewing gum to be unaesthetic and annoying, but dentists have long known that sugar-free gum reduces the incidence of cavities.25 In addition, a few experiments have shown that children who chew hard, resinous gum grow larger jaws and have straighter teeth.5224
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Like any other system of the body, the developing immune system needs to interact with the environment in order to match capacity appropriately with demand.5247
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If you were breast-fed, you were also kept healthy by your mother’s milk, which is loaded with antibodies and other protective factors, providing an immunological umbrella.5255
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The idea that a certain amount of filth is both normal and necessary to develop a healthy immune system has come to be known as the hygiene hypothesis.5259
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Ever since bleach, sterilization, and antibiotic soaps made our environments more germ-free, children’s immune systems have had more unemployed T-helper 2 cells swimming about, increasing the likelihood that one of them will make a terrible mistake and wrongly target a harmless substance as an enemy. Once this happens, an allergy develops.5300
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In the not-too-distant future, your doctor may prescribe you worms or feces.5321
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there is good reason to believe that asthma and other allergies are mismatch diseases in which too little exposure to microorganisms contribute to an imbalance that, paradoxically, causes too much of a response to otherwise harmless foreign substances.5322
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Just as children need the right kinds of food and exercise, it appears that they also need the right kinds of microorganisms in their guts and respiratory tracts. Further, when they get sick and require antibiotics (which do save lives), perhaps the antibiotic prescriptions should always be followed by probiotic prescriptions to restore old friends and help keep their immune systems appropriately occupied.5332
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we have become reasonably proficient at treating or coping with most of their symptoms, but we do little to prevent their causes, sometimes because of ignorance.
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none of the mismatch diseases discussed above normally affect people’s reproductive fitness (the one exception is an extreme untreated allergic reaction). One can live for years with osteoporosis, bad teeth, and certain allergies.
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for all these diseases, the relationship between the environmental causes of the mismatch and the physiological effects are gradual, obscure, delayed, marginal, or indirect, and many of them are promoted to some extent by cultural factors we value, such as eating delicious processed food, minimizing toil, and being clean.5349
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many of these problems stem from a basic, common urge to avoid stress and mess.5354
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just because we can live lives of exceptional cleanliness and comfort doesn’t mean they are good for us, especially children. To grow properly, almost every part of the body needs to be stressed appropriately by interactions with the outside world.5357
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Consider any individual at any period of his life, and you will always find him preoccupied with fresh plans to increase his comfort. —ALEXIS DE TOCQUEVILLE, Democracy in America5380
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We habitually value costs and benefits more highly in the near term than in the future (economists call this behavior hyperbolic discounting), allowing us to appear more rational about our long-term goals than our less rational immediate desires, actions, and pleasures. As a result, we tolerate or take pleasure in potentially harmful things because they enhance our lives now more than what we judge to be their eventual costs or risks.5394
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none of these conditions, including the fact that you are sitting and reading, are actually normal for a human being,5415
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our bodies aren’t well adapted for novelties such as reading, sitting too much, and drinking soda.5416
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the second evolutionary explanation for why humans often do novel, potentially harmful things: we frequently mistake comfort for well-being.5420
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Comfort is also profitable.5431
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the drawback of thick-soled shoes is that they limit sensory perception. You have a rich, extensive network of nerves on the bottom of your feet that provides vital information to your brain about the ground beneath you and that activates key reflexes that help you avoid injury5470
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you can actually avoid any impact peak at all if you land on the ball of the foot before bringing down the heel, in what is known as a forefoot strike.5490
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running, which is really just jumping from one leg to the other.5495
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Many of the world’s best and fastest runners forefoot strike even when they are wearing shoes.5501
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Harvard cross country team who heel strike are injured more than twice as frequently as those who forefoot strike.5513
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I have almost never seen a flat arch in any habitually barefoot person, reinforcing my belief that flat feet are an evolutionary mismatch.5532
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In short, many people suffer from foot problems because our feet evolved to be bare. Minimal shoes have been around for many thousands of years, yet some modern shoes designed for a combination of comfort and style can interfere substantially with the foot’s natural functions.5563
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it is healthy to encourage infants and children to go barefoot and to ensure that children’s shoes are minimal so their feet develop properly and become strong.5568
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In the United States and Europe, nearly a third of children between the age of seven and seventeen become nearsighted (myopic) and need glasses to see properly; the percentage of myopic people is higher in some Asian countries.5583
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rates of myopia are less than 3 percent among hunter-gatherers and in populations that practice subsistence agriculture.5587
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myopia among Europeans used to be uncommon except among the educated upper classes.5588
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the recent worldwide epidemic of myopia must result primarily from environmental shifts. Of all the factors identified, the most commonly identified culprit is close work: intent focusing for long periods of time on nearby images such as sewing and words on a page or screen.5601
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important cause may be a lack of sufficiently intense and diverse visual stimuli during childhood and adolescence.5607
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children who spend more time inside than outdoors are more likely to get myopia.5658
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hypothesis that eyeglasses have caused coevolution. As a reminder, this kind of evolution occurs when cultural developments actually stimulate natural selection on genes,5673
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two facts are clear. First, myopia is a formerly rare evolutionary mismatch that is exacerbated by modern environments. Second, even though we don’t entirely understand which factors cause children’s eyeballs to elongate too much, we do know how to treat the symptoms of myopia effectively with eyeglasses.5695
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For every hour you sit at a desk, you spend about 20 fewer calories than if you were to stand, because you are no longer tensing muscles in your legs, back, and shoulder, as you support and shift your weight.5736
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Standing for eight hours a day adds up to 160 calories, the equivalent of a half-hour walk.5738
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back pain around the world consistently find that back pain is twice as high in developed versus less developed countries; further, within low-income countries, the incidence is roughly twice as high in urban versus rural areas.5781
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hunter-gatherers use their backs moderately—neither as intensively as subsistence farmers nor as minimally as sedentary office workers.5793
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the relationship between physical activity levels and back injury. Individuals with very low and high levels of activity have higher risk of injury but for different reasons.5808
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therapies that improve back strength, including low-impact aerobic exercise, appear to be effective ways to improve back health.5820
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cultural selection does not always operate with the same criteria as natural selection. Whereas natural selection only favors novel mutations that enhance an organism’s abilities to survive and reproduce, cultural selection can promote novel behaviors simply because they are popular, lucrative, or otherwise beneficial.5836
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Our bodies were simply not adapted by millions of years of evolution to handle many modern technologies, at least not in extreme quantities or degrees. Consider the three examples highlighted in this chapter: wearing shoes, reading, and sitting in chairs.5845
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we might be able to avoid some foot problems by encouraging people—especially children—to go barefoot more often and to wear more minimal shoes (this hypothesis has yet to be tested).5861
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The last few thousand years of cultural evolution have significantly altered the human body’s condition, sometimes for the worse (especially initially), but eventually and mostly for the better. Because of farming, industrialization, sanitation, new technologies, improved social institutions, and other cultural developments, we have more food, more energy, less work, and additional blessings that immeasurably enrich and improve our existence. Billions of people now take for granted a long life and good health.5880
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the rate and power of cultural evolution has vastly outpaced the rate and power of natural selection, and the bodies we inherited are still adapted to a significant extent to the various and diverse environmental conditions in which we evolved over millions of years.5900
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The principal trade-off between the novel environments we have created and the bodies we inherited has been mismatch diseases.5908
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The next generation of Americans risks being the first generation to live shorter lives than their parents.5921
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In 1209, a Catholic army massacred between ten and twenty thousand people in the city of Béziers, France, in an effort to stamp out heresy. Since it was not possible to distinguish the faithful from the heretics, the slaughterers were reportedly told to “kill them all and let God sort them out.”5949
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natural selection is basically the inevitable outcome of two phenomena that still exist: heritable variation and differential reproductive success.5954
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Human evolution is not over, but the chances of natural selection adapting our species in dramatic, major ways to common noninfectious mismatch diseases are remote unless conditions change dramatically.
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One reason is that many of these diseases have little to no effect on fertility. Type 2 diabetes, for example, generally develops after people have reproduced, and even then, it is highly manageable for many years.8
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Another consideration is that natural selection can act only on variations that affect reproductive success and that are also genetically passed from parent to offspring. Some obesity-related illnesses can hinder reproductive function, but these problems have strong environmental causes.9
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Finally, although culture sometimes spurs selection, it is also a powerful buffer. Every year new products and therapies are being developed that allow people with common mismatch diseases to cope better with their symptoms. Whatever selection is operating is probably occurring at a pace too slow to measure in our lifetimes.5966
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Quick fixes for complex diseases may be a dangerous form of science fiction,5982
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Good old-fashioned diet and exercise are not panaceas, but dozens of studies unambiguously prove they substantially reduce the rate of most common mismatch diseases.6002
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Prevention really is the most powerful medicine, but we as a species consistently lack the political or psychological will to act preventively in our own best interests.6008
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long-term intervention study showed that adult Americans who were unfit but then improved their level of fitness halved their rates of cardiovascular disease.15 Because it costs an extra $18,000 a year to treat an American with heart disease, one can estimate that persuading just 25 percent more of the population to become fit could save in excess of $58 billion per year for just heart disease care alone.6015
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a 2008 study estimated that spending $10 per year per person in community-based programs that increase physical activity, prevent smoking, and improve nutrition would save the United States more than $16 billion per year in health-care costs within five years.6022
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Americans know they should be physically active and eat a healthy diet, yet only 20 percent of Americans meet the government’s recommendations for physical activity, and fewer than 20 percent meet government dietary guidelines.6031
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It does not take a multimillion-dollar study to know that we should not have unrealistic expectations about behavioral changes even if we improve the quality and reach of health education.6074
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children and adults instinctively prefer foods that we evolved to crave (sweet, starchy, salty, and fatty) and that factors such as advertising, range of available choices, peer pressure, and cost strongly affect modern foraging decisions.6078
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When I can choose between taking an escalator or the stairs, I almost always prefer the escalator. I am in the majority. Moreover, banners and posters in malls designed to encourage shoppers to take stairs instead of escalators increase stair climbing by only 6 percent, which is about as effective as mass media campaigns that try to promote physical activity.6080
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Numerous experiments have proved that humans behave in many ways that are beyond our conscious control. We react through instinct. These snap judgments tend to be for common, repetitive, instantaneous decisions such as whether to eat the chocolate cake or the celery, or whether to take the stairs or the elevator.6084
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we consistently discount the value of rewards in the present (such as one more cookie) relative to rewards in the distant future (such as health during old age) in proportion to the length of the delay.6088
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we constantly make irrational decisions through no fault of our own.6091
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1. For the foreseeable future, people will continue to get sick from mismatch diseases.
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2. Future advancements in medical science will continue to improve our ability to diagnose and treat the symptoms of mismatch diseases but will not devise many actual cures.
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3. Efforts to educate people about diet, nutrition, and other ways to promote health will have limited effects on their behavior in current environments.6099
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Freedom is more precious than good health,6112
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since all diseases result from gene-environment interactions, and we cannot reengineer our genes, the most effective way to prevent mismatch diseases is to reengineer our environments.6114
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“You are free to do as you wish as long as I don’t have to pay for it.”)6142
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if cultural evolution got us into this mess, then shouldn’t cultural evolution be able to get us out?6177
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Today we need to innovate and cooperate in new ways to avoid eating too much food, especially excess sugar and processed industrial foods, and to survive in cities, suburbs, and other unnatural environments.6179
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For millions of years, our ancestors were required to consume a naturally healthy diet and to be physically active.6187
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Some people erroneously think that natural selection means “survival of the fittest.” Darwin never used that phrase (it was coined in 1864 by Hebert Spencer), nor would he have, because natural selection is better described as “survival of the fitter.” Natural selection doesn’t produce perfection; it only weeds out those unlucky enough to be less fit than others.6196
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“Nothing in biology makes sense except in the light of evolution.”6201
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if there is any one most transformative human adaptation that we evolved it must be our ability to evolve through culture rather than just natural selection.6207
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Today, cultural evolution is outpacing and sometimes outwitting natural selection.6208
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culture does not allow us to transcend our biology.6216
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Like it or not, we are slightly fat, furless, bipedal primates who crave sugar, salt, fat, and starch, but we are still adapted to eating a diverse diet of fibrous fruits and vegetables, nuts, seeds, tubers, and lean meat. We enjoy rest and relaxation, but our bodies are still those of endurance athletes evolved to walk many miles a day and often run, as well as dig, climb, and carry. We love many comforts, but we are not well adapted to spend our days indoors in chairs, wearing supportive shoes, staring at books or screens for hours on end. As a result, billions of people suffer from diseases of affluence, novelty, and disuse that used to be rare or unknown. We then treat the symptoms of these diseases because it is easier, more profitable, and more urgent than treating their causes, many of which we don’t understand anyway. In doing so, we perpetuate a pernicious feedback loop—dysevolution—between culture and biology.6219
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Daniel Lieberman is professor of Human Evolutionary Biology, and the Edwin M. Lerner II Professor of Biological Sciences, at Harvard.11103
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(earning him the nickname the Barefoot Professor).11105
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