Why are humans hairless? Why is childbirth so painful, and dangerous? Why is the human intellect so highly developed? Because we run.
A herder from the Afar region of Ethiopia
The Perfect Runner cracks open the modern-day sport of endurance running by exploring our evolutionary past as a species formed and defined by long-distance running adaptations. New archaeological research into the physiology of early hominids and a deeper understanding of climate conditions at critical points in our evolution are now revealing that two critical adaptations occurred simultaneously to produce modern Homo sapiens. The first was the transformation between 3 and 2 millions years ago of the tree-climbing body of our Australopithecus predecessors into the bipedal body we possess today. The second was the development of the large Homo brain, and the reasoning and language abilities it enabled. The order and cause of these changes have spurred debate for decades, but now some scientists are arguing neither would have been possible without a critical third adaptation, namely a supreme advantage over other animals bestowed by our ability to run long distances.
The emergence of Homo sapiens
The famous Australopithecene skeleton we call Lucy, discovered in the Ethiopian portion of Africa's Great Rift Valley, reveals that 3.2 millions years ago, our ancestors moved in a vertical world. With short legs, a wide waist, long arms and grasping toes, Lucy would have waddled as she walked, recruiting her arms alongside her legs for faster movement. Her elongate feet and side-pointing big toes would have made running almost impossible. Yet in a tree canopy, her compact body would have given her elegance and strength.
But Lucy's world was changing. By 2.5 million years ago, the Modern Ice Age had begun, and the dense forests of sub-Saharan Africa gave way to open savannah as the climate cooled and became more arid. The protective tree-canopy environment of the African Australopethecine was disappearing, and Lucy's descendents were forced to survive on the ground or perish. At just this juncture, our hominid ancestors rapidly changed in form. A string of bipedal apes evolved along a path that led to Homo sapiens, but as they did, our ancestors' body began making a series of bizarre, counterintuitive tradeoffs – adaptations that would seem to make survival less likely.
Archaeological evidence dating to the emergence of Homo predecessors within the last two million years ago reveals that we were also becoming carnivores, feasting on bone marrow, brain, and meat. In some form, human hunter-gatherer cultures were emerging. But in the highly competitive savannah environment, teeming with predators more formidable at running down food and defending their kills than humans, how did our ancestors do it?
The perfect runner
In fact, far from maladaptating into vulnerable and underpowered land walkers, Homo had come out the trees to emerge as a masterful endurance runner. They were no rival to lions, wildebeast and kudu antelope in speed and manoeuverability, but over long distances, humans evolved to outrun any animal in their African surroundings.
The body of Homo sapiens can do two things remarkably well: stride efficiently and regulate body temperature. The human leg, from the build of the arched foot to the network of long tendons running up the calf and thigh, is a perfectly formed marriage of muscle and energy-returning "springs". The large bum muscle – the gluteus maximus – is unique to humans among the primates and propels us forward while stabilizing our torso as we stride. A large rope – the nuchal ligament – runs up the back of the head to stabilize the cranium during running. Our withered arms, in comparison to our primate cousins, are structured to swing as counterweights to our body's motion without tiring our shoulders. And our elongate form – long legs, narrow hip, tall torso – give an elite runner a stride length of 3.5 metres, much farther than any four-legged competitor.
Yet many other animals boast running mechanics just as impressive; what really sets humans apart is our ability to stay cool. In African mid-day temperatures of over 35 degrees Celsius, the upright elongate body is itself an advantage, exposing less body surface to direct sunlight and rising higher above the baking ground. With no body hair and more sweat production per unit surface area than any other animal, as well as highly vascular noses and crania, humans are exquisitely good at unloading body heat. We have even evolved to withstand a higher body temperature then our mammal competitors; the normal eutherian mammal body core temperate is 36-38 degrees Celsius, whereas humans can withstand heat stresses above 42 degrees.
Running to survive – evolutionary dimensions
If Homo emerged as the supreme endurance runner of the African savannah, how did this adaptation fit into our evolutionary history? How was it related to the emergence of human intellect, which is ultimately the supreme characteristic of modern humans?
Seboka Negusse, a human body built for running
Dan Leiberman and Dennis Bramble, two leading proponents of the "born to run" hypothesis, speculate that because the growth of the human brain proceeded after the emergence of the running body, it was not our intellect that first guaranteed our survival on the ground. On the other hand, neither was bipedal locomotion – the ability to walk – enough to protect early Homo as we shifted from forests to open savannah. Relentless natural selection promoted the survival of runners; the Homo body form emerged rapidly in response to the changed environment, a classic evolutionary "state shift".
The archaeological record shows that by this point, 2.4 million years ago, humans were consuming a high-protein diet of meat, bone marrow and brain. Although this diet was costly, in terms of the energy required to hunt or scavenge, our ancestors were now up to the challenge. Most likely, we became highly efficient scavengers, running after fresh kills when circling carrion birds alerted us to their existence. But a high-protein diet also set the stage for another evolutionary leap. Now the Homo brain, whose tissue per gram demands 24 times energy than skeletal muscle, was free to develop and expand. Human intellect rewarded us with language and reasoning ability, which when paired with our ability to outrun other animals allowed us to move beyond scavenging. For the past 2 million years, humans have proactively hunted the four-legged animals in our environment, and it appears we did it by running. Using a practice called "persistence hunting", hunters tracked and ran their prey to exhaustion. We can infer this because while we were eating meat from our first days as Homo, sophisticated tool cultures emerged only about 200,000 years ago; before this, the human body itself was our primary weapon.
Anthropologists know of persistence hunting by its survival until recently in cultures ranging from the Tarahumara of northern Mexico to the Bushmen of the Kalihari to the Aborigines of northern Australia. South African anthropologist Louis Liebenberg was able to study Kalihari persistence hunting in the 1980s, and his account provides a critical corroboration of the theory of endurance running in human evolution. Bushmen hunters operated in teams of 3-5 men, all expert trackers possessing a high level of accumulated knowledge of both the behaviour of their various prey species and the landscape they hunted within. The hunt would begin in the heat of the day, typically in temperatures of 39 degrees or higher. Choosing prey like zebra, duiker, eland or even cheetah, they would force the animal to run without rest for up to 35 kilometres, eventually causing it to collapse with heat exhaustion. The kill, when the animal reached this state, was simple; the animal was already nearly dead.
In the 1980s, Liebenberg documented the last known persistence hunts anywhere on the planet. We now live in a world that rewards the accomplishments of intellect rather than the ability to run down animals. Nevertheless, we possess the same Homo body, more or less, that emerged millions of years ago on the African savannah. Although in the ways we live our lives very few of us acknowledge it, we are still runners.
Our running past in the present day
As we become increasingly divorced from our essence as a running animal, we are plagued with "diseases of affluence." Our bodies are evolved to manage, and in fact require, extended periods of intense cardiovascular stress. Sedentary lifestyles have spawned epidemics of heart disease and diabetes, the limits of which we have yet to reach. The lesson, as health professionals know, is that the one kind of behaviour our bodies cannot withstand is inactivity. It is the daily routine of urban office workers that is extreme, not the life of a long-distance runner.
But as if we can sense an echo in our own bodies of our hunter-gatherer past, more of us are taking up the running all the time. And herein lies a paradox: we hear the call of our running past, yet we treat running as a modern invention, requiring highly engineered shoes. We wonder how runners coped before the arrival of the cushioned running shoe in the 1970s. But research is now revealing that cushioned running shoes, and the practice of striking the ground heel-first that they encourage, is contributing to running injuries, not preventing them.
Before the invention of cushioned running shoes, runners typically adopted a forefoot or midfoot strike. This is the running style the body automatically assumes when its feet are unprotected. In developing countries like Ethiopia, most runners still spend their early years running barefoot or sandaled, and use the same forefoot-strike technique. Research by Harvard professor Daniel Lieberman published in Nature has revealed that the impact force absorbed by the body is considerably higher when heel-strike running, regardless of shoe protection, than when forefoot-strike running. He believes this accounts for the spiralling incidence of repetitive stress injuries among runners today.
Despite the promotion of "correcting" running shoes by a multi-billion dollar industry, two million years of evolutionary success as an endurance-running species have given our feet and ankles extraordinary natural shock resistance. The arched structure of the foot and the flexion abilities of the ankle joint work together to absorb the impact of the foot strike while maintaining a natural leg position. This force is then partially returned as the foot propels off the ground. The heel strike, in contrast, transmits impact force straight up the leg to the knee and hips while braking the forward momentum of the runner. As medical research catches up with the biomechanical advantages of "natural running", more and more specialists are advising runners to turn away from highly engineered running shoes and return to the forefoot-strike technique in more minimal footwear. The boom in "barefoot running" is one reflection of this trend.
Meanwhile, in the world of elite endurance running, coaches have been taking cues from natural runners for decades, learning from the success of the Ethiopian, Kenyan and Moroccan athletes who dominate the international top ranks. At North America's Athletics Coaching Centre at the University of Alberta, a long-standing collaboration with Ethiopian runners, including the legendary Haile Gebreselassie, has insured that the rising generation of North American athletes emulates the best African runners. Coaches eschew cushioned running shoes, concentrate on foot strength, use barefoot running as a training method, and always promote forefoot-strike technique.
The rest of us, encouraged by "advances" in running shoe technology, have adopted a running style humans were never evolved to withstand. Once again, we are paying a steep price for ignoring our evolutionary hardwiring; we should run as our ancestors did, with as little on the foot as possible.
- Niobe Thompson