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 abou.