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.

Tuesday, April 20, 2010

My Use of Timelines in the Classroom

For much of my life, I have been fascinated by human prehistory. I don’t know when this started. It may have been a result of my reading Jacob Bronowski’s The Ascent of Man, a pun on Darwin’s famous Descent of Man. I read that book in high school, which traced humanity’s development of knowledge through science and was based on a 13-part BBC series which I never saw. I did very little reading of any kind in high school, but I remember that my father gave me that book and I couldn’t put it down. It was fascinating. During college a few years later, I took a course in human evolution and at one point while reading about the evolution of the remarkable human hand, I stopped what I was doing and stared in wonder at my own hand. I graduated from college with a topical bachelor’s degree in “Prehistoric Studies,” something which embarrassed me and which I therefore conveniently changed to “Cultural Anthropology” when anybody asked about my college major. Once while living in Peru, I stayed up late with a couple of friends who shared the pension with me in downtown Lima. As the evening wore on, I eventually launched into a very animated lecture about human prehistory, physically acting out all the stages of human evolution from Ramapithecus to the present. It may have been my very first successful lecture on the subject. My small audience talked about that incident for weeks. (Here's a short, 4-minute lecture on human prehistory using a timeline analogy:

When I taught 5th grade in 2003, I had to delve a little into prehistory to introduce my class to the early Native Americans of California. We made a timeline beginning with the earliest human settlement in our local community of Topanga Canyon, something we discovered while reading about an archaeological spot called the ‘Tank Site.’ The dig took place in the late 1940s, and was situated only a few miles from our school. We read about it in a chapter from our local historical society’s book, The Topanga Story. The Tank Site was first inhabited by native peoples over 7,000 years earlier. I wanted our class timeline to begin with those first known inhabitants of Topanga, continue up through the earliest Europeans to homestead in the area (the Santa Maria family), and end with the present era. I determined that I would need enough space on the timeline to plot important historic events such as the Revolutionary and Civil wars, as well as Westward Expansion, since these were also required subjects for 5th-grade social studies. I figured that 10 feet of timeline would suffice to chart these latter historical events. However, I wanted the timeline to be accurately ‘to scale,’ meaning it didn’t compress time at any point like so many timelines found in textbooks. As a math assignment, I had students calculate the total length of the timeline from the present back to the Tank Site, with at least 10 feet reserved for the most recent 200 years of our history. This meant that each foot had to represent 20 years of history, which is roughly one human generation. Several days were devoted to planning this timeline, determining its length, assembling materials (stacks and stacks of old homework were creatively glued together by teams of students), and figuring out how to hang this long timeline from the walls our room. In the end, the timeline was over 350 feet long, and spiraled a couple of times around the high walls in our large brick classroom. It was a dramatic sight, and impressive to see how the native peoples had inhabited the timeline for over 340 feet, while Europeans only begun homesteading within the last 7 feet of the timeline. The timeline created quite an impression about the longevity of the native population when compared to the recent European settlers. Sometimes we would play the ‘foot’ game, where we would randomly mark a short foot-long section of the timeline at any point along its 350-foot length. We would then make up a story about a group of native peoples who lived during that 20 year period, what adventures they had, what animals they hunted and plants they gathered, who grew up into what kind of person, what stories were told, what difficulties were encountered, and what dreams and visions were held. This helped us to give life to the timeline and the people who lived for so many generations before European contact.

The following year, when I taught 6th grade, timeline activities became more dramatic. Social Studies for 6th grade requires more than just a look at Native Americans, but involves the study of human prehistory back through our split from the apes. Suddenly a 7,000 year timeline was replaced with a 3.7 million year-long timeline. This ancient date marked the moment when two bipedal (fully upright) early hominids (human ancestors) left very human-looking footprints in some fresh volcanic ash in what is now Laetoli, Tanzania, Africa. Because those Australopithecine footprints were so well-preserved and carefully photographed when they were discovered in 1976, I knew that such an event would make a dramatic visual beginning for our human evolution timeline in 6th grade. On this timeline, I planned to have students plot the first stone tools (about 2.5 millions years ago), the discovery of fire (700,000 years ago), the emergence of modern humans (200,000 years ago), the earliest cave paintings (about 40,000 years ago), the first farming communities and civilizations (beginning about 11,000 years ago), the discovery of coal power (the Industrial Revolution), and up to the present day. As 6th-grade prehistory covered a much greater period of time, with a total span of years much longer than it had been in 5th grade, the students’ ability to conceptualize these numbers and to construct an accurate timeline, represented an immense challenge.

In much of my work with 6th graders, conceptualizing numbers of great size has always been extremely difficult. Whether we are making timelines of human history, studying the distance to ‘nearby’ stars, or discussing the numbers of casualties from disasters like the South-Asian tsunami, large numbers are simply too hard to fathom. Yet in spite of the difficulty, I have discovered that challenging ourselves to make these leaps of mind, to represent these models of size and distance, is intellectually enabling, cognitively captivating, and emotionally stimulating. If we were to take the previous year’s 350-foot timeline -which stretched almost three times around my room winding for 7,000 years down to the prehistoric Tank Site natives- and continued that timeline back to the fossilized African footprints of early ancient humans, the timeline would obviously be much, much longer. But just how long? This is where numbers become hard to grasp. Keeping the timeline to scale, it would now stretch over 185,000 feet in length, continuing on for 35 miles! This means that a timeline of human history -in which the last 200 years compressed to 10 feet of timeline- would have to be 35 miles long in order to trace our history back to our earliest upright ancestors, 24 miles long to go back to the first stone tool makers, and 7 miles long to take us back to the controlled use of fire by Homo erectus. It was clearly impossible to make a 35-mile timeline, but the message was clear; human beings and their most recent upright ancestors, inhabited the earth for far longer than most of us had ever been able to appreciate. As a class, we ended up making a more compressed timeline in our room that stretched just 120 feet around the room, and upon which all of human history back to Africa’s “Lucy” (Australopithecus) was contained. On such a timeline, each foot of distance now represented 30,000 years of history. On this timeline, the emergence of farming, human settlements, and all of human civilization was contained within the last four inches. On this timeline, the industrial revolution occurred within the last one-tenth of an inch. A new and dramatic message emerged from this timeline; During 120 feet of the timeline, human ancestors lived in nomadic, hunting-and-gathering groups, but such a tribal, foraging lifestyle was abandoned during only the last few inches of human history. Industrialization and environmental destruction had only begun within the last fraction of an inch. Such a timeline revealed some compelling truths about our species, illustrating how recently we have dramatically changed have the way we relate to the earth, to nature, and to each other.