This book looks at human evolution with a special emphasis on the ways our bodies aren’t adapted to the modern world. It defines dysevolution as the mismatch of present day culture and circumstances interacting with the human body in a harmful way. Cultural evolution happens at an exponentially faster pace compared to biological evolution and so our bodies haven’t caught up to modern living or diets. Because of this, many of today’s most common ailments are caused by the way we live. Cancer, diabetes, heart disease, myopia, and tooth decay are all discussed, among others.
Ozzy TEDMED: The Prince of Darkness’ genome is examined.
What the professionals had to say: The Washington Post review.
Buy on Amazon: The Story of the Human Body: Evolution, Health, and Disease
Stuff of Interest:
Pangloss— The professor in Candide, who is an eternal optimist.
mellifluous—sweet or musical; pleasant to hear.
nascent— just coming into existence and beginning to display signs of future potential.
yaws—the nonvenereal precursor of syphilis, still common in tropical countries.
Sahelanthropus tchadensis—6 to 7 million year old ancestor of humanity.
australopith—4 million year old ancestor of humanity.
phenotypic plasticity—the capacity for bodies to adjust their observable characteristics (their phenotype) in response to environmental stresses. (Example: children who exercise more from an early age develop thicker bones, just as children raised in hot climates develop more sweat glands).
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. Our bodies have a story—an evolutionary story—that matters intensely. For one, evolution explains why our bodies are the way they are, and thus yields clues on how to avoid getting sick. Why are we so liable to become fat? Why do we sometimes choke on our food? Why do we have arches in our feet that flatten? Why do we have backs that ache? A related reason to consider the human body’s evolutionary story is to help understand what our bodies are and are not adapted for.
Evolution is simply change over time.
The final and most important point about adaptation is really a crucial caveat: no organism is primarily adapted to be healthy, long-lived, happy, or to achieve many other goals for which people strive. As a reminder, adaptations are features shaped by natural selection that promote relative reproductive success (fitness). Consequentially, adaptations evolve to promote health, longevity, and happiness only insofar as these qualities benefit an individual’s ability to have more surviving offspring. To return to an earlier topic, humans evolved to be prone to obesity not because excess fat makes us healthy, but because it increases fertility. Along the same lines, 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. And we not only evolved to cooperate, innovate, communicate, and nurture, but also to cheat, steal, lie, and murder. The bottom line is that many human adaptations did not necessarily evolve to promote physical or mental well-being.
Because of a massive volcanic hotspot, the entire region was pushed upward like a souffle, and then (like some souffles) the central portion collapsed, forming the Great Rift Valley. The Rift Valley created an extensive rain shadow, drying out much of eastern Africa. The Rift Valley also harbored many lakes, which to this day continue to fill up and then drain out in cycles. Although eastern Africa’s climate was constantly changing, the overall trend was that forests shrank while woodlands, grasslands, and other more arid, seasonal habitats expanded. By 2 million years ago, the region looked much more like the set of The Lion King than Tarzan.
When an ape or dog breathes in through its nose, air flows in a straight line through the nostrils and into the inner nose. But when humans inhale nasally, the air goes up through the nostrils, takes a 90-degree turn, and then goes through another pair of valves to reach the inner nose. These unusual features cause the air to swirl in chaotic vortices. Although this turbulence requires the lungs to work. Mucus holds lots of water but not very strongly. So when you inhale hot, dry air through an external nose, the resulting turbulent flow enhances the inner nose’s ability to humidify the air. Such humidification is important because inspired air needs to be saturated with water to prevent the lungs from drying out. Just as importantly, the turbulence helps the nose recapture that moisture when we exhale. The evolution of large external noses in early Homo is strong evidence for selection to walk long distances in hot, dry conditions without dehydrating.
One of the most important adaptations for human running is our unique ability to cool by sweating instead of panting, thanks to millions of sweat glands combined with a lack of fur. Most mammals have sweat glands on just their palms, but apes and Old World monkeys have some sweat glands elsewhere on their bodies, and at some point in human evolution we exuberantly augmented the number of glands to between 5 and 10 million. When we heat up, sweat glands secrete mostly water onto the body’s surface. When the sweat evaporates, it cools the skin, the blood beneath, and then the entire body. Humans can sweat more than a liter per hour, enough to cool an athlete running hard in hot conditions. Even though the temperature at the 2004 Olympic women’s marathon in Athens reached 35 degrees Celsius (95 degrees Fahrenheit), high sweat rates enabled the winner to run at an average speed of 17.3 kilometers (10.7 miles) per hour for more than two hours without overheating! 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.
In fact, a running human’s legs store and release energy so efficiently that running is only about 30 to 50 percent more costly than walking in the endurance-speed range. What’s more, these springs are so effective that they make the cost of human endurance running (but not sprinting) independent of speed: it costs the same number of calories to run five miles at a pace of either 7 or 10 minutes per mile, a phenomenon many people find counterintuitive.
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 Security Council, choking on food is the fourth leading cause of accidental deaths in the United States, approximately one-tenth the number of death caused by motor vehicles. We have paid a heavy price for speaking more clearly.
We lack accurate data on the world’s population before modern censuses, but educated guesses suggest that the number of humans living had multiplied at least a hundredfold from just 5 or6 million people at 12,000 years ago to 600 million at the time of Jesus’s birth; by the start of the nineteenth century, the world probably had approximately 1 billion people.
Consider malnutrition, a problem that confronts farmers more than hunter-gatherers, because the way farmers rely on a few staple foods decreases their diets’ nutritional diversity and quality. One example is pellagra, a horrible illness from insufficient vitamin B3 (niacin), which causes diarrhea, dementia, skin rashes, and eventually death if untreated. Pellagra is common among farmers who eat mostly corn (maize) because vitamin B3 in corn is bound to other proteins, making it unavailable to the human digestive system. Native American farmers never evolved genes that would give them resistance to pellagra, but they did learn long ago to make a special kind of corn flour, called masa flour, by soaking the corn in an alkali solution before grinding. This process (termed nixtamalization) not only liberates vitamin B3 for digestion but also increases the corn’s calcium content.
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.
History teaches us that ordinary people can grow accustomed to horrible, normally unthinkable events—what the philosopher Hannah Arendt called “the banality of evil.” Evolutionary logic suggests that humans becomes accustomed to novel, unhealthy behaviors and aspects of our environment when they become quotidian.
In the United States and many other countries, health care is partly a for-profit industry. Consequently, there is a strong incentive to invest in or promote treatments such as antacids and orthotics that alleviate the symptoms of diseases and that people have to buy frequently and for many years. Another way to make lots of money is to favor costly procedures like surgery instead of less expensive preventative treatments like physical therapy. Preventative medicine is also distorted by profit. Dieting, for example, is a multibillion-dollar industry in America and elsewhere, largely because most diets are ineffective, and overweight people are willing to keep spending lots of money on new diet plans, many of which are literally too good to be true.
Most people don’t get sick through any fault of their own, but instead they acquire chronic illnesses as they age because they grew up in an environment that encourages, entices, and sometimes even forces them to become sick. For many of these diseases, we can then only treat the symptoms. Unless we want to end up as a species ever more dependent on medicines and expensive technologies to cope with the symptoms of preventable diseases, we need to change our environments. In fact, it is questionable whether we can continue to afford the cost of our current trajectory of increased longevity and population sizes combined with increased chronic morbidity.