Read an Excerpt
Chapter 1
Our Bodies Are Older Than We Think
Nothing in biology makes sense except in the light of evolution.
- Theodosius Dobzhansky
MYTH: Life spans have increased compared with decades ago.
FACT: When chronic disease and declining public health are factored in, modern life spans aren’t much longer than they used to be. By some measures, average functional life spans in the United States have started to decline.
Whether your goal is athletic dominance or simply to arrive at a healthy old age, we all share the goal of making the best of our lives while on the planet, in the healthiest and most productive way that we can.
Let’s start by inspecting the miraculous equipment we inherited, to better understand what it is that our bodies were designed to do.
Running Is Only Human
Throughout human history—for almost 2 million years as hunter-gatherers, followed by 12,000 years as pastoralists and farmers—our ability to run, to walk, and to be physically active has been essential to life. By virtue of our existence—indeed, as evidenced by our domination of the planet—humans are succeeding. So far, at least.
Our prehuman, primate ancestors were slower and weaker than many of the large animals that they eventually would learn to prey upon. Masters of agility, their bodies and limbs were adapted mainly for living in trees, where they could find forage and fruit, and were safe from nonclimbing predators that lived on the forest floor.
So how did they come to dominate these other species, prey upon them, and even drive some of them to extinction? And later, what enabled modern humans, Homo sapiens, to win the evolution race with earlier species of our genus? Was it brains over brawn, or the other way around? Or did our brawn and brains coevolve?
By nearly every metric of human strength and performance, early hominids (and even one extinct line, the Neanderthals) were superior to Homo sapiens. We made an incremental yet critical adaptation by gradually becoming able to walk and run long distances.
Scientists generally believe that the ability to walk and run on two feet was a game changer. With the rudimentary tools avail-able to early humans, it would have been difficult and dangerous to bring down an antelope. Yet there’s evidence that humans were killing and eating large prey for some time before spears and other weapons were developed.
One compelling theory proposes that early humans’ ability to walk (and occasionally run) long distances in hot climates allowed them to track large, fast prey until the animals dropped of heat exhaustion and dehydration, unable to run or to fight. Doing so at a walking pace wouldn’t have been sufficient. Early humans sprinted when escaping a predator or other imminent dangers. But when tracking game, according to the “persistence hunting” theory, they would have needed to travel only fast enough to keep their prey moving and not resting. (Most large animals shed heat by panting, yet they are unable to pant while running.)
Our ability to travel long distances in an energy-efficient manner helped us with more than hunting. It also allowed us to relocate more readily to a new water source, for instance, or travel to a more bountiful area. Essentially, we could walk away from perils such as famine and drought, sometimes to distant locations, aided by an ability to efficiently store and utilize the calories we consumed.
We Got the Right Gear
Dr. Dan Lieberman and colleagues have identified evolutionary adaptations in our anatomy and physiology that enhance our ability to walk and run long distances. Mainly, we benefited from the following features, which you may even begin to notice as you pay attention to your running:
- Springy tendons and muscles in the legs that work in efficient harmony. As the springlike, fibrous tendons stretch, they load up with potential energy. The muscles contribute to stability at the same time that the tendons spring us forward.
- Extra-large gluteus maximus, or butt muscles, that make for strong and stable hips and trunk.
- An upright posture, exceptional balance, and a stable head and neck. Notice that these features enable us, while running on two feet, to remain simultaneously aware of our surroundings and focused on a distant object. Some believe that our well-developed vestibular system (the region of the inner ear that controls balance) may have contributed substantially to our survival success.
- Sweat glands, which humans have an abundance of. Sweating provides effective evaporative cooling, or thermoregulation. We adapt to heat by perspiring more as the temperature and our activity levels rise. Our absence of fur, minimal body hair, and high surface-area-to-body-weight ratio mean that more skin is exposed to the air’s cooling effect. Also, uniquely, our breathing pattern is uncoupled from our stride, so we can unload body heat through our lungs during respiration, which four-legged mammals cannot.
- The capacity to digest, store, and utilize fat as an efficient source of fuel. Fat contains twice the calories per gram as sugar. That fat is metabolized with seven to ten times greater efficiency than sugar, too. (We’ll explore this valuable fuel source in the chapters on endurance and nutrition.)
- Feet that are uniquely adapted to walking and running, with their springlike arches and short toes. Each foot is an orchestra of 26 bones, 33 joints, 107 ligaments, and 19 muscles and tendons, providing cushioning, spring, and control in three planes simultaneously. Chapter 4 is devoted to this remarkable appendage.
Slow, But Smart
Despite all of our evolutionary adaptations, humans would appear to be physiologically flawed. Raising our young to adulthood requires (nonproductive) years of nurturing and training, and our top speed is slow when compared to similar-sized wild animals.
Natural selection entails trade-offs and compromise. Humans have developed great endurance, but we aren’t very fast. (The fastest land animal, the cheetah, is specialized for catching prey with speed but has little endurance.) And the human ability to efficiently store fat is useful for surviving famines, yet comes with a high risk of obesity. Even brain size offers a trade-off: the large human brain is a hungry organ, consuming about a quarter of the body’s resting energy demand—diverting calories that might be more productively dedicated to strength and speed.
Nonetheless, our brains have served us well. Our evolving brains led to the harnessing of fire, and the cooking, grinding, and mashing of foods with tools. Softening tough plant and animal fibers sped up the process of chewing and digestion, so greater quantities of protein and fat can be metabolized by the body. (Cooked foods yield more than twice the usable nutrition of raw foods: cellulose and the proteins of muscle fiber denature at high temperatures, making them softer and easier for the body to digest.)
The nutritional boost from consuming higher-quality food supported the development of more brain power. As humans grew smarter, their socialization, hunting skills, and tool-making abilities improved. Meanwhile, the control of fire helped with more than cooking: the deterrent effect of fire on wild animals allowed humans to sleep longer without fear of predators. Deeper REM sleep further aided brain function and growth.
Along the way, humans became fat-storing and fat-burning machines. Fats and proteins offer the critical building blocks for brain and muscle, and fat is more energy- and essential nutrient–dense than carbohydrates. The Inuit, for example, remained healthy without consuming any carbohydrates. Humans cannot survive without fat.
Early humans also developed an ability to store (energy-poor) carbohydrates by efficiently converting them to (energy-rich) fat, with the help of insulin. In times of plenty we could accumulate fat, then metabolize it in times of need—drawing upon it over periods without food, if necessary, before needing to “refuel.”
Nature or Nurture?
Individual performance varies, and this variation can be partly explained by genes. But lifestyle, diet, and behavior matter, too. A journalist named Adharanand Finn observed the strenuous, physically active lives of rural Kenyan children, many of whom chase goats and livestock at home, then run long distances to and from school. These children have little access to television or computers, and virtually all of them are barefoot. One Kenyan tribe in particular has consistently produced running champions—the Kalenjin. Their steely determination and active rural lifestyle appear to have converged to make them the fastest endurance runners in the world.
Similarly, the Tarahumara of Mexico are famous for covering extraordinary distances wearing sandals made of old tires and rope. When Tarahumara legend Arnulfo Quimare spoke at the 2016 Boston Marathon, a runner in the audience asked about his “training” regimen. Through a translator (who had to pause to find the suitable word), Arnulfo replied that his “training” consisted mostly of walking from village to village.
When it comes to running, there’s no evidence that the Tarahumara or the Kenyans are genetically superior to anyone else. Harvard evolutionary biologist Daniel Lieberman points out that people in these groups are prone, like all of us, to habits that can lead to illness and poor running technique, especially when they adopt Western diets and modern running shoes.
Competing Evolutionary Intentions
We evolved to run, to walk, and to remain active. At the same time, we were born to conserve energy whenever possible—to rest and relax. In the calorie-shy world of our ancestors, the ability to reduce caloric expenditure, and to store that energy through periods of no food, conferred survival advantages. For modern humans, however, this genetic tendency to pack away calories has created something of an evolutionary dilemma. Researcher James H. O’Keefe and his colleagues describe a “millennia-old connection—the balance between energy expenditure, calorie ingestion, and appropriate hormonal responses.” In other words, the connection between our inner nature and the environment we live in has largely been severed. “Until a century or so ago,” O’Keefe says, “never before in history have humans been routinely exposed to high caloric, highly processed foods in excess of the calories needed to function.” (This may have been true for most, but not all. Dr. Michael Eades often speaks of the mummified evidence and artistic renditions of the farinaceous Egyptian culture. A high body weight may have been a sign of wealth and status, though it appears that a far smaller percentage of people were overweight in earlier times.)
We’re beginning to see that this inborn proclivity to take the path of least resistance and eat as much as we desire plays a major role in the health woes and rising health care costs beleaguering modern people. Obesity and high-sugar diets create fertile ground for a variety of modern diseases, especially type 2 diabetes. We’ll address this in the chapters on nutrition and diet.
Therein lies the inspiration for this book: the hope that we can become better, more functional, healthier humans—and restore and nurture our connection to who we are and to how we were meant to live. This doesn’t mean finding a place of stasis and comfort. It demands that we actively resist the inborn desire to remain on the couch and eat whatever is within reach.
We’re living in a unique time in human history, one in which we have a choice of lifestyles. Our bodies didn’t evolve to sit all day at a desk, though many of us do. Nor, admittedly, did we evolve to be ultra-marathon-running machines, though I have occasionally aspired to be such, and have enjoyed the adventure. Our goal should be to find a place in between, and to adopt a lifestyle that matches what our bodies were designed for. Homeostasis with hormesis as the path to excellence.
New Old Routines
The daily routines we have fallen into over the past several generations have perpetuated a number of habits that are harmful to our health. Not only have our diets, sleep patterns, and anxiety levels changed, but the ways we move our bodies (or don’t move them) have drifted from the natural, ergonomically efficient patterns of our ancestors. One example is sitting, which I discuss in chapter 3, on posture and walking. If we sit in a slumped position— head and shoulders forward, hips flexed, and glutes overstretched—we develop a muscle memory that disrupts our standing posture. We become misaligned, and all of our movements suffer.
Technological aids and interventions don’t help. Drugs, orthotics, gimmicks, supplements, and fads that promise to compensate for our declining mobility and health mainly serve to accelerate our bodies’ physiological drift. These expensive “fixes” seldom correct the underlying problems, which often originate in poor posture, incorrect movement, and unhealthy behavior. Many of the mod-ern medical interventions, too, merely accommodate our ancient human bodies to a very different modern world. We end up with growing instances of what Dr. Lieberman has termed “mismatch diseases,” afflictions resulting from behavior, movement patterns, and diet that don’t match the physiology (and psychology) of the bodies and minds we inherited from our ancestors.
Quality of Life: More Important than Quantity
Despite all this medical attention, the disability-adjusted life expectancy (DALE) and the health-adjusted life expectancy (HALE) for Americans is only seventy years, which doesn’t even figure into the global top twenty. And if you discount only two developments of the last century—the significant reduction in infant mortality, and the singular lifesaving qualities of antibiotics—life spans today aren’t all that much longer than they were generations ago.
By some measures, average functional life spans in the United States have started to decline. This refers to the length of one’s healthy, active life, in contrast to the total number of years that one has been alive. In light of this, Orville Rogers, a one-hundred-year-old Masters record holder in the 200-meter run, quipped that our goal should be to “live long and die short.”
How do we do that? Researcher James O’Keefe points out that the daily physical activity pattern of hunter-gatherers forms an ideal template from which to design a modern exercise regimen—one that works to realign our daily movement with the archetype encoded within our genome. Indeed, the drills at the end of each chapter have premodern counterparts. For instance, endurance training (long, slow runs) was essential for persistence hunting; interval training (jogging punctuated with short sprints) corresponds to fighting and fleeing; strength training (such as lifting weights) replicates house building or handling large game; and mobility training (moving the body through its full range of motion) reproduces a variety of movements needed for survival. Rest and recovery is included front and center in this template: hunter-gatherers spent plenty of time relaxing, too.
I’m convinced that to avoid the tantalizing perils of the convenient modern age, we need to reclaim a bit of our evolutionary past—by eating simple, natural foods, and by regularly putting our bodies through a wide range of movements. Throughout, hopefully, we’ll also experience a sense of enjoyment and play. (In recent generations, this has been re-created in the context of sports.)
Fortunately, even low to moderate levels of exercise, sports, or exertion at your job can improve your health. This simple message isn’t always self-evident in a society that assumes more is better and faster is best. As a doctor attempting to reintroduce the concepts of simplicity, consistency, and modest effort, I sometimes feel “old school,” swimming against a tide of fads, assumptions, quick fixes, hacks, New Age remedies, and popular theories.
You’re about to learn more about the miracle of human mechanics and enjoy the art, the mechanics, and the plain old addictive pleasure of walking and running, which is ingrained in our DNA.
Let’s get started.
