Wednesday, April 28, 2010

Long Distance Running in Human Evolution

Human omnivory is a touchy subject. With the increasing popularity of vegetarianism, an odd mythology has crept into the human culture arguing that human beings are actually more herbivorous than omnivorous, or that vegetarianism is more ‘natural.’ However comforting this may be in a world where violence has become so random and uncontained, the truth is that human beings evolved as hunters. Consider this: Each of us has our own sequence of ancestors going back into history to the time of the first fully-upright, stone tool makers. It’s akin to our own personal family tree. To take our father’s father’s father, etc., all the way back to those makers of the early hand axes, we’d have quite a long line of ancestors, roughly 125,000 of them, assuming a new generation is born about every 20 years. Of these ancestors, only 600 have lived since the time of agriculture. Over 99% of them were nomadic hunter-gatherers who lived in small tribes. To compress this number of ancestors to just 200, we alone would be the first and only ones to not live as a nomadic hunters. We are the embodied product of a sequence of evolutionary events that included a long tenure as hunters. Much of our physical morphology and many of our psychological mechanisms are a result of having evolved as predatory hunters. I believe we will all be better off if we can embrace this truth about ourselves, and further, if we can accept that hunting itself is not necessarily a kind of barbarism or wayward atavism. To dismiss hunting as just more human violence, is to negate who we are and where we came from. Many people, especially urban dwellers, regard the hunting of animals as a chilling reminder of humankind’s less admirable traits. This is perhaps a consequence of a glorification of killing evident in ‘trophy’ hunting, and the popularization of sportsman programs and publications. It may be because of the blood spilled in hunting, or the result of a deep desire to remove ourselves from death and from nature.

A healthier, or more ‘natural’ hunting is expressed in a subtle predator-prey relationship steeped in a rich and complex symbolism. It is something very different from random or gratuitous violence. We must acknowledge that no life is sustained by ingesting inorganic matter. Even vegetarians kill in order to live. This is a fundamental truth of the biosphere on planet earth; all life consumes life. Of course the killing of animals is more messy than uprooting asparagus. Also, we easily feel that the intelligence and physical complexity of animals makes their life more precious than the life of plants whose consciousness –if they have any at all- must be far different from ours. There is also the idea that plants were simply made to be eaten, as if this functionality precludes carnivory. There is a spiritual side to hunting that is not simply an approbation to justify the killing of animals. And this does not mean that all hunters are spiritual.

Physically speaking, probably the most striking evidence of our hunting past is one of the least obvious. Indeed, it has been overlooked until very recently. For centuries, when a biologist would distinguish the human species from all other animals, she would discuss our large brains, describe how we can walk on two legs, and reference our impressive tool making abilities. But dolphins have large brains, birds walk on two legs, and monkeys fashion tools. What really distinguishes humans, at least in a physical sense? What evolved morphological features most set us apart from the entire animal kingdom? The simple answer is: our ability to run long distances. With regular training, humans can outrun any animal on the planet in an endurance race. We can even best horses and dogs, two avid long-distance runners. Ultramarathoners run 100-mile races. Pam Reed, at age 42, ran 300 miles without stopping.

We now know that running evolved separately from walking. Running requires a kind of locomotion completely distinct from walking, meaning that different features in the body allow for running while others provide for the mechanics of walking. And human beings don’t only run, we run far. We have spring-loaded tendons which compress on the downstride to give tremendous propulsion on extension. We are covered in sweat glands and have evolved a remarkable hairlessness, both physical features which strongly inhibit hyperthermia. Unique among higher primates, our skulls are oddly detached skeletally from our shoulders, and we have an unusual ligament on the back of out necks (the nuchal ligament), long dismissed as relatively functionless. We now know that the free skull supported in the back by the nuchal ligament, is a critical adaptation for keeping our heads level and sustaining our visual acuity while running. Our waists are oddly narrow in relation to our shoulders, a unique feature among primates and important to balance in running. We have a very large gluteus maximus muscle, necessary for supporting the trunk while running. We have one of the strangest respiratory systems among mammals in that we can synchronize our breathing with our stride, fully oxygenating our blood on the fly. Nearly all quadrupeds cannot sprint while breathing through their mouths like humans, and must rest regularly to regain their necessary blood oxygen levels. When quadrupeds enter a full run, they go anaerobic.

Our running abilities have always been made light of. Even apes and chimps can outsprint us, and compared with the other great predators –the wolves and large cats- we are very slow runners. It has always been assumed that we became successful hunters because we had such large brains and were able to outsmart our prey –using the elements of surprise, ingenious traps, or powerful weapons. Indeed, these are all important features in the successful enterprise of hunting, but they are not critical. Our brains did not become married to surprise, traps and weapons to bring down large predators. Rather we used our cunning, our wits, our tenacity, and our ability to track, together with our unprecedented physical stamina and endurance capabilities, to engage in what we call now the ‘persistence hunt.”

Paleontologists have long been curious how human ancestors consumed animal meat before the invention of large projectile spears. Such weapons appeared just 200,000 years ago, but the bones of large animals show signs of scraping fully 2 million years ago. Also, to grow and sustain large brains required huge amounts of high-quality protein. We didn’t evolve these brains overnight during just the last 200,000 years of evolutionary history. So it has puzzled paleontologists how we managed to eat meat and evolve large brains –clearly a response to a diet rich in animal protein- if we were simply scavenging the corpses of big game, or nibbling rabbit bones and eating bugs and lizards. Where did we find an abundant source of protein-rich meat for those nearly 2 million years that we lived without throwing spears and without bows and arrows? We now know that humans evolved the capacity to run long distances, to follow game for hours on end, to chase them repeatedly during the course of many hours under a bright, hot sun. Humans evolved endurance running capabilities as an adaptation to the demands of a protein-hungry brain, and during the course of 2 million years of our history we brought down large game by chasing those ungulates and other quadruped to exhaustion. This was the persistence hunt. The Kalihari San Bushmen of Africa, the Australian Aborigines, and certain Native Americans living in the mountainous areas of northern Mexico, still regularly engaged in the persistence hunt during this past century, though only recently have we come to appreciative the role of this type of hunting in propelling our uniquely human evolution.

Click here to watch a short BBC video about persistence hunters.

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