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Comparison between walking and running of mechanical energy expended. Credit: Daniel Lieberman
Ann Trason, Scott Jurek, Matt Carpenter. These are the megastars of ultra-distance running, athletes who pound out not just marathons, but dozens of them back-to-back, over Rocky Mountain passes and across the scorching floor of Death Valley. If their names are unfamiliar, it’s probably because this type of extreme running is almost universally seen as a fringe sport, the habit of the superhumanly fit, the masochistic, the slightly deranged.
But a handful of scientists think that these ultra-marathoners are using their bodies just as our hominid forbears once did, a theory known as the endurance running hypothesis (ER). ER proponents believe that being able to run for extended lengths of time is an adapted trait, most likely for obtaining food, and was the catalyst that forced Homo erectus to evolve from its apelike ancestors. Over time, the survival of the swift-footed shaped the anatomy of modern humans, giving us a body that is difficult to explain absent a marathoning past.
Our toes, for instance, are shorter and stubbier than those of nearly all other primates, including chimpanzees, a trait that has long been attributed to our committed bipedalism. But a study published in the March 1 issue of the Journal of Experimental Biology, by anthropologists Daniel Lieberman and Campbell Rolian, provides evidence that short toes make human feet exquisitely suited to substantial amounts of running. In tests where 15 subjects ran and walked on pressure-sensitive treadmills, Lieberman and Rolian found that toe length had no effect on walking. Yet when the subjects were running, an increase in toe length of just 20 percent doubled the amount of mechanical work, meaning that the longer-toed subjects required more metabolic energy, and each footfall produced more shock.
“If you have very long toes, the moment of force acting on the foot’s metatarsal phalangeal joint becomes problematic when running,” explains Lieberman. Our hominid ancestors, Australopithecus, of which Lucy is the most famous specimen, had significantly longer toes than humans. “Lucy could have walked just fine with her long toes,” says Lieberman. “But if she wanted to run a marathon, or even a half-marathon, she’d have had trouble.”
The March study is the first attempt to assess the ER hypothesis using an experimental approach, but the idea that humans have a marathoning past first surfaced more than two decades ago, when David Carrier, a runner and grad student in the lab of evolutionary biologist Dennis Bramble, convinced his mentor that running ability might explain a number of unique human features. Over the years, Bramble’s team at the University of Utah and Lieberman’s team at Harvard have amassed a small ream of physiological and morphological evidence that they believe points to a distance-running legacy. In 2004 the groups copublished a list of 26 such markers on the human body, including short toes, a hefty gluteus maximus and Achilles tendon, springy tendon-loaded legs, and the little-known nuchal ligament that stabilizes the head when it’s in rapid motion.
The paper earned the cover of Nature and generated quite a stir within bio/anthro circles. But it did nothing to answer a fundamental question: What good would endurance running have been to primitive man? On an evolutionary battleground — where the struggle is to eat or be eaten — speed, and not endurance, should be the prized trait. If a tiger in high gear could outpace Homo erectus within 10 seconds and a deer in 20, being able to run at a modest pace for hours at a time does not seem like an evolutionary advantage.
shoothead via Flickr
Christopher McDougall came up against this very conundrum in his spirited book Born to Run (Knopf, May 2009). McDougall, neither anthropologist nor biologist, is a journalist originally given an assignment for Runner’s World that morphed into a consuming fascination with feats of high mileage, particularly with that of the Mexican Tarahumara Indians, reclusive canyon dwellers reputed to be the best endurance athletes on earth. Wearing shoes fashioned from tire strips to cushion their feet, the Tarahumara cover up to 400 miles in festive, multiday events drawing runners and spectators from multiple villages. They are also the picture of health, enjoying almost total immunity to cancer and the diseases that plague modern society. For McDougall, the Tarahumara seem to confirm what Lieberman has been arguing all along, that humans are built for running. To find out why, McDougall inevitably found his way to the Harvard researcher, who shared with him an intriguing theory.
We know that roughly 2 million years ago, Australopithecus, with its tiny brain, hefty jaw and diet of rough, fibrous plants, evolved into Homo erectus, our slim, long-legged ancestor with a big brain and small teeth suited for tearing into animal and fruit flesh. Such a transformation almost certainly involved a reliable supply of calorie-laden meat, yet according to the fossil record, spear points have been in use for 200,000 years at most, and the bow and arrow for only 50,000 years, leaving an enormous stretch of time when early humans were consuming meat without the use of tools. Lieberman believes they ran their prey to death, often called “persistence hunting.”
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