Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live (20 page)

A 2011 study by Graeme Ruxton and David Wilkinson used mathematical models to determine whether it would have been feasible for early humans to lose enough heat while running to maintain a fairly high pace during persistence hunting.
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Taking into account the air and ground temperatures, the amount of heat lost from a mostly hairless body, and a few other variables, the scientists concluded that persistence hunting would have been effective only after humans had already evolved the ability to run long distances. This means that the Endurance Running Hypothesis might be putting the runner before his finish line, so to speak. Ruxton and Wilkinson caution that their results depend on several assumptions, as with all theoretical models, and that what we really need is more information about questions such as how dehydration affected running ability (it’s doubtful that early hominins stashed water to be available during the length of a hunt), or how the relatively tall, narrow bodies of humans influence heat loss.

Were we, then, lean, tireless running machines, or robust animals that ran only far enough to find a stone for constructing a spearhead? I am convinced by the data in our bones and muscles; humans possess traits that simply work better for running than walking, and these traits aren’t shared by our closest ancestors. We certainly did not evolve to be sedentary. Beyond that, it seems reasonable to suggest that we didn’t run for a set period each day, like someone training for a race, but no one knows whether humans exercised like Grok. Developing elaborate scenarios about lifting boulders or walking with weights is getting into the realm of paleofantasy, and it seems like a pointless—ahem—exercise.

Greg Downey, an anthropologist at Macquarie University in Australia, suggests a sensible compromise:

Long-range endurance running wouldn’t have just been for hunting: humans cover immense ranges, even when foraging and scavenging . . . Endurance running may have been a relatively rare, but important trick, and distance running also might be useful for drop hunting (chasing animals over cliffs), for defense (run until a predator just gives up), communication, expanding our effective scavenging range, etc. . . . From our perspective from the couch, I think it’s too easy to underestimate just how good we are as runners.
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Feet and the lawns of the Pleistocene

Regardless of whether we evolved running short distances or long ones, we certainly did not evolve to run, or walk, with shoes, and that simple observation leads to one of the biggest controversies among runners and athletes today. Part of why it is difficult for many people to imagine that the human body is “born to run” is the frequency of foot and leg pain and injuries among recreational and professional runners. A 1992 survey of the medical literature estimated that 37–56 percent of runners suffer injuries yearly,
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and a 1989 examination of 583 “habitual runners” over the course of a year found that about half reported injuries severe enough to seek medical attention, take medication, or limit their activities.
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Shoe manufacturers have risen to the challenge with ever more elaborate cushioning, lacing designs, and other scaffolding intended to keep the foot stable during motion. And people are happily, or at least willingly, going along for the race. In 2009, consumers spent $2.36 billion on jogging and running footwear, up from $987 million in 1988.
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A 2011
New York Times
article noted that even in that year’s sluggish economy, sales of running shoes were “sprinting along,” having increased as much as 18 percent over the previous year.
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But the shoes that are selling the best are those that look nothing like traditional running shoes, with their elevated heel and thick layers of padding. Instead, the new models are minimalist, including the Vibram FiveFingers, which looks more or less like a glove for the feet, with a separate slot for each toe and a very thin sole. These shoes are designed to mimic running barefoot, which Christopher McDougall and many other proponents suggest is a more natural way to run. McDougall’s website bluntly states, “The notion that the human foot is inherently flawed and automatically needs some kind of corrective device is kind of nuts.”
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Barefoot running is a logical consequence of the idea that humans evolved to run long distances; if the whole process is artificial, then wearing special gear makes sense, just as it does for ballerinas donning pointe shoes; they couldn’t perform as required without assistance. But if running is how we are built, then the fancy equipment may be superfluous, like attaching helium balloons to a bird’s wing.

McDougall points to the Tarahumara of Mexico, who run either barefoot or with very thin sandals for up to 100 miles over rocky terrain. He and others also note that little evidence exists that wearing shoes actually prevents injury.
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One study published found that shoes costing more than $90 were associated with more than two times as many injuries as the cheapest models.

As McDougall and others, including Lieberman, who is also a barefoot-running aficionado, are quick to point out, the real difference is not so much the shoe as the technique one uses while wearing (or not wearing) it. Shod runners tend to strike the ground more heavily, with their heel first, while barefoot runners land more springily, on the mid- or forefoot. It is this gentler method that seems to be the key to avoiding injury. In keeping with this idea, a 2011 study of women runners who tried out minimalist shoes found that if they didn’t change their form to land on the ball of the foot, they still had hard landings and high impact.
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Lieberman and a host of colleagues set out to examine this idea by comparing the gaits of both barefoot and shod runners in Kenya and the United States.
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They calculated the collision strike force for five groups of people who all ran at least 20 kilometers each week: athletes from Kenya’s Rift Valley, who had grown up without shoes but now ran with them; two groups of schoolchildren from the same place, one of which had never worn shoes and one of which were mostly shod; American athletes who had once run in standard shoes but who now ran either with minimalist shoes or barefoot; and American athletes who routinely wore shoes. The barefoot runners tended to hit the ground with the forefoot, with occasional midfoot or heel strikes, whereas the shod runners were primarily heel strikers, with more impact and jarring of the body. It’s that forceful collision, Lieberman and his coworkers claim, that causes runners the most harm. If a runner takes off his or her shoes but doesn’t adjust technique, injuries are still likely.

Interestingly, the forefoot- and midfoot-striking runners in Lieberman’s research had softer landings even on hard surfaces. In many discussions of barefoot versus shod running, contributors on either side point out that going without shoes was fine back when our ancestors were doing it, but we did not evolve to run on concrete or other hard surfaces. But as McDougall states on his website, “What soft, grassy fantasy land did they come from? Check out the sun-baked African savannah sometime: hard as cement. Or the stone trails of Mexico’s Copper Canyons, or the packed dirt roads of Ancient Greece.”
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Certainly some runners simply want a bit of protection to keep their feet away from broken glass or burning cigarette butts, unarguably not Pleistocene hazards. Nevertheless, the argument that barefoot running was all well and good back in the day when the soft Paleolithic soil yielded under our feet, but not now, is, well, a paleofantasy.

A 2011 review from the
Journal of the American Podiatric Medical Association
was fairly noncommittal on the topic of barefoot running but noted that “many of the claimed disadvantages to barefoot running are not supported by the literature.”
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The authors found no increase in shin splints and other injuries among barefoot runners, for example.

People who take up barefoot running seem to become evangelical about it, touting the joy of feeling the trail under their bare feet. One commentator on the
New York Times
Well
health blog said, “Running on a regular basis may not work out for you, but never forsake the barefoot experience . . . except in restaurants and the Opera/ballet, and presidential luncheons.”
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In the meantime, sales of minimalist “barefoot style” shoes were up 283 percent in 2011 over the previous year, and the arguments continue to rage. As another
Well
blog reader said, “I’d like to see scientists measure levels of smugness and self-righteousness in barefoot vs. shod runners.”
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The real problem with trying to characterize the natural foot or its gait, however, is that feet, like other components of our bodies, do not develop in a vacuum. If you put those adorable tiny shoes on a toddler’s feet, the shoes alter the growth pattern of those feet. If you don’t put shoes on them, the growth pattern is still altered—by the surface the child walks on, by the amount of time the child spends doing different activities, and so on. Downey points out that feet can perform all kinds of tasks, including painting or typing on a keypad, by people whose arms or hands are disabled. “The fact that skills like foot painting or feeding oneself with one’s feet are rare does not mean that our feet were not ‘designed’ to do them,” he says.
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Even with the same genes, one person’s foot can become adept at running, another’s can learn to excel at playing an instrument, and yet another’s can become atrophied if it is bound according to ancient Chinese practice. Our genes had this responsiveness in the Pleistocene as well, making it impossible to isolate a single “most natural” exercise pattern.

Genes, muscles, and a race for the future

Finally, what about our running future? Is our ability to exercise itself able to evolve? Scientists are finding intriguing hints of the kind of genetic variation that is the fodder for evolutionary change. Assuming, of course, that we can overcome the sedentary siren call of our couches.

Athletic ability hasn’t shown the kind of clear-cut, widespread genetic shifts in distinct populations that lactose tolerance has, but people obviously differ in their ability to perform physical tasks, and at least some of that ability is founded in the genes. And while parents who gaze admiringly on a tot as she flings strained peas have always dreamed of the WNBA, now they can actually test the genes of their tiny would-be athlete to see if those dreams are likely to be realized. Or, to be more accurate, a test is available. Whether it really guarantees a career on the court is another matter.

The gene in question is called
ACTN3
, and it is responsible for the production of a protein that controls fast-twitch muscle fibers. Muscle tissue exists as strings of molecules that can contract quickly or slowly; the fast-twitch type is important in activities requiring bursts of power, such as sprinting. Some people have a variant of the gene that disables such fast-twitch fibers, and if they have two copies of the variant, they tend to have slightly weaker muscles and run slightly slower, though the variant is also more likely to be found in endurance athletes such as marathon runners. The gene variant influences the muscles by making them more efficient at aerobic metabolism, the kind of metabolism used during endurance activities. The variant is present at different frequencies in people from different parts of the world, with, for example, about 18 percent of those from European ancestry but only 10 percent of Africans possessing it.
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Australian researcher Daniel MacArthur and his colleagues studied
ACTN3
both in humans and in mice that they genetically engineered to lack the protein.
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The mice without the protein could run 33 percent farther than mice with the more normal gene configuration, which presumably would correspond to mice that were better at running the rodent equivalent of a marathon. Mice with the variant also had 6–7 percent less grip strength, though they were still well within normal mouse capacity.

The scientists then reasoned that if variation in the type of
ACTN3
present influenced running performance, and the percentage of people with the variant differed across the globe, it should be possible to determine whether
ACTN3
evolved recently because of natural selection on muscle ability. To test their hypothesis, they did the same analysis of the genes surrounding the
ACTN3
gene that I described for lactose tolerance in Chapter 4, looking to see whether the neighboring genes were swept along as selection for the chunk of DNA containing
ACTN3
was favored. Indeed, the gene variant seems to have become much more common over a relatively short period in European and Asian populations.
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As might be expected, Olympic sprinters were less likely to have the variant than Olympic endurance athletes, though the athletes did not show a single genetic profile even for
ACTN3
. Studies of a handful of other genes have suggested a disproportionate frequency in elite athletes, leading a group of Spanish researchers to ask whether there is an optimal genetic profile for such people. Led by Jonatan Ruiz and Alejandro Lucia, the Spanish team examined 46 “world-class endurance athletes,” including both endurance runners and professional cyclists, all of whom had participated in either an Olympic final event or a Tour de France, and 123 “non-athletic (sedentary) controls.”
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Although the athletes tended to be more likely to have favorable genes for performance, no one had the perfect profile, and the authors suggest that genetic variants “yet undiscovered as well as several factors independent of genetic endowment may explain why some individuals reach the upper end of the endurance performance continuum.”

This conclusion should come as no surprise to anyone who has trained for an athletic event or watched someone else do so. Which brings us back to the idea of whether it is worth testing little Sally to see if she should be sent to Olympic summer camp. In MacArthur’s opinion, the answer is a flat-out no. In an article on Wired.com, he says, “
This is not a test that can tell parents whether or not their kid will be able to become an elite athlete in general.
No matter what your
ACTN3
genotype is, there is a wide range of sports that you could theoretically excel in” (emphasis in the original).
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Too many genes, not to mention environmental factors, contribute to athleticism to make testing for a tiny variation productive.