📖 Notes & Highlights

• As more people are living longer and fewer are dying young from diseases caused by infections or insufficient food, exponentially more middle-aged and elderly people are suffering from chronic noninfectious diseases that used to be rare or unknown.

• Lower mortality is being replaced by higher morbidity (ill health).

• Evolution is simply change over time.

• Our species’ proclivities to be worried, anxious, and stressed cause much misery and unhappiness, but they are ancient adaptations to avoid or cope with danger.

• Becoming bipedal creatures separated the human lineage off on a separate evolutionary path from other apes.

• One major drawback of becoming bipedal is coping with pregnancy. The extra weight in the mother’s abdomen shifts her center of gravity well in front of the hips and feet. This causes her to lean backward, shifting her center of mass back over her hips. This places extra shearing stresses on the lumbar vertebrae.

  • Being biped also costs humans speed. Not being able to gallop limited our early ancestors to being about half as fast as a typical ape when sprinting. In addition, two limbs are much less stable than four and make it harder to turn quickly when running.

• During walking, legs function like pendulums that alternate their center of rotation. When the leg is swinging forward, the center of rotation is the hip. But when the leg is on the ground and supporting the body above, it becomes an upside-down pendulum whose center of rotation is the ankle. This reversal allows us and other mammals to save energy with a clever trick.

• Wide hips that face sideways allow the muscles along the side of the hip to stabilize the upper body when only one leg is on the ground. Without this shape, we’d always be in danger of falling sideways, and we’d have to waddle awkwardly like a chimp.

• In terms of advantages, tramping around upright makes it easier to carry food, and a vertical posture exposes less surface area to the sun, which means that bipeds heat up less than quadrupeds from solar radiation.

• You have a long, flexible lower back, an arch in your foot, a waist, a big knee, and many other features that help make you an excellent long-distance walker.

• Hunting and gathering is an integrated system with four essential components: gathering plant foods, hunting for meat, intensive cooperation, and food processing.

• The advantages of eating plants are that one can reliably predict where to find them, they are often relatively abundant, and they don’t run away. A big disadvantage of plant foods, especially non-domesticated plants, is that they are high in undigestible fiber and have a comparatively low nutrient density.

• Archaeological sites dated to at least 2.6 million years ago, possibly older, include animal bones with cut marks that were created when simple stone tools were used to cut the flesh away. We therefore have irrefutable evidence that hominins started to consume meat at least 2.6 million years ago.

• Since the cost of moving the body a given distance is priced by the step, longer legs reduce the cost of walking.

• Since bipedal hominins cannot sprint very fast, the ability to walk long distances during the day without overheating was probably a critical adaptation for the early hunter-gatherers in Africa, allowing them to forage when carnivores were least likely to kill them.

• 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.

• Humans can run long distances at speeds that require quadrupeds to switch from a trot to a gallop. Running humans cool by sweating, but four-legged animals cool by panting, which they cannot do while galloping. Therefore, 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.

• Around 500,000 years ago archaic Homo invented a new and ingenious method of fabricating very thin stone tools with predetermined shapes, including triangular points.

• A human brain is full-sized by six or seven years, but obviously, a six-year-old child’s brain and body require another dozen years or more to develop completely.

• There is good reason to hypothesize that without our ability and proclivity to stockpile fat, archaic humans could never have evolved big brains and slow-growing bodies.

• Only one out of every six hundred of your base pairs differs from Neanderthal DNA.

• There is good reason to believe that modern environments contribute to a sizeable percentage of mental illnesses, such as anxiety and depressive disorders.

• Although scientific fields such as physiology and biochemistry can help us understand the proximate mechanisms that underlie a disease, the burgeoning field of evolutionary medicine helps us make sense of why the disease occurs in the first place.

• More food is good, but agricultural diets can provoke mismatch diseases. One of the biggest problems is a loss of nutritional variety and quality.

• 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.

• Living in larger, denser communities is socially stimulating and economically profitable, but such communities also pose life-threatening health hazards. The biggest peril is contagion.

• The Industrial Revolution was an economic and technological revolution in which humans started to use fossil fuels to generate power for machines to manufacture and transport things in massive quantities.

• Sugar has become so superabundant and so cheap that the average American consumes more than 100 pounds a year.

• You probably take for granted the use of a flush toilet, but until the late nineteenth century, clean places to defecate were luxuries, and the technology to keep human waste away from drinking water was primitive and ineffectual.

• Unlike glucose, which can be metabolized by cells throughout the body, fructose is almost entirely metabolized by the liver. The liver, however, can burn only so much fructose at once, so it converts any excess fructose into fat, which again is either stored in the liver or dumped into the bloodstream.

• Fiber makes up the walls of the cells that encase the sugars in the apple, slowing the rate at which you break down carbohydrates into sugar.

• 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.

• Because of fiber, a raw apple’s fructose is digested gradually and thus arrives more slowly at the liver. As a result, the liver has plenty of time to cope with the apple’s fructose and can readily burn it at a leisurely pace. However, when processed foods deluge the liver with too much fructose too quickly, the liver is overwhelmed and converts most of the fructose into fat (triglycerides).

• Dark skin prevents your skin from burning, but limits how much vitamin D you synthesize.

• Tooth shape is mostly controlled by genes, but proper tooth position in the jaw is heavily influenced by chewing forces.

• Humans have been walking and running on their bare feet for millions of years, and many people still do.

• Beyond considerations of style, the most important function of shoes is to protect the soles of your feet. The feet of unshod people and other animals accomplish this function with calluses, which are made of keratin, a flexible hairlike protein that also makes up rhino horns and horse hooves.

• 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 injury when you sense something sharp, uneven, or hot underfoot.

• Many of the world’s best and fastest runners forefoot strike even when they are wearing shoes.

• Heel striking is easier on the Achilles tendon.

• The bottom line is that whether you forefoot strike or heel strike, you should do so gently, and being barefoot gives you less choice. Runners who generate higher, more rapid impact peaks are significantly more likely to accumulate repetitive stress injuries in their feet, shins, knees, and lower back.

• Just as a neck brace relieves your neck muscles from supporting your head, an arch support in your shoe relieves the foot’s ligaments and muscles from having to hold up the arch. Arch supports are therefore built into many shoes because they lessen how much work the foot’s muscles have to do.

• Some people’s genes may predispose them to getting flat feet, but the problem is mostly caused by weak foot muscles, which otherwise help create and maintain the shape of the arch. Studies that compare habitually barefoot and shod people have found that barefoot people almost never have flat feet but instead have much more consistently shaped arches, neither low nor high.

• Strong, flexible feet are healthy feet, but instead of strengthening their patients’ feet, many podiatrists prescribe orthotics and advise patients to wear comfortable shoes with arch supports and stiff soles.

• Narrow toe boxes unnaturally scrunch the front of the foot and contribute to common problems such as bunions, misaligned toes, and hammertoes.

• In short, many people suffer from foot problems because our feet evolved to be bare.

• Most cases of nearsightedness occur when the eyeball grows too long. When this happens the lens can still focus on nearby objects by contracting the ciliary muscles, which allows the lens to become more convex. However, when someone with an overly long eyeball tries to focus on a distant object by relaxing the ciliary muscles, the focus point of the flattened lens falls short of the retina.

• Eyeglasses are just simple lenses that bend waves of light before they hit the eyeball, moving the point of focus back onto the retina.

• Squatting and sitting on the ground or even on a stool requires more postural control from a variety of muscles in the back and abdomen, helping to maintain their strength.

• A healthy back requires an appropriate balance between how much you use your back and how well your back functions.