Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live (19 page)

How did early humans use their flexibility in running speed, good endurance, and a superior ability to shed heat? According to the Endurance Running Hypothesis, the point wasn’t running Stone Age marathons but hunting prey. When they are first startled by a predator, most prey animals sprint away, relying on speed to escape. But they tire after a relatively short period, and if they have not shaken the predator, the hunter can start to close in. Furthermore, most prey animals start to overheat after they have been running for a while, and will attempt to rest. If the hunter can keep after the prey, and not overheat itself, eventually it can catch up to its quarry, not because it is faster, but because the prey animal has started to develop heat exhaustion. So, humans evolved to be long-distance runners as a way to get food, and many of the other adaptations, such as our superior sweating ability, followed. Bramble and Lieberman conclude their paper by suggesting that endurance running allowed humans to acquire the protein- and fat-rich diet that many anthropologists believe allowed the evolution of our big brains.
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The process, logically enough called persistence hunting, actually sounds rather diabolical. Carrier points out that if early humans had the same cost of transport at various speeds, then they could “have picked the speed least economical for a particular prey type. This would have forced the prey to run inefficiently, expediting its eventual fatigue.”
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Keeping after an animal and not allowing it to rest when its temperature rises too much is more important, and more feasible, than overtaking it. In other words, running fast is not enough; you have to also run smart.

Running smart includes more than running; if you aren’t at the heels of your prey every instant, you need to be able to track it, and tracking is a skill that comes only with long experience. It involves not only tracing the signs of an animal’s passage through the wilderness by detecting subtle changes in soil or vegetation, but predicting where the animal is likely to go and keeping it away from shelter or even the safety of its fellow group members. Such tracking ability, not to mention persistence hunting itself, is rare among modern people, but Louis Liebenberg, a scientist and tracking expert from South Africa, has documented it in the Kalahari bushmen.

Over a six-year period, Liebenberg worked with several hunters in central Botswana, participating in some hunts and assisting filmmakers on others. When they were chasing large antelopes such as kudus, three or four men would drink as much water as they could and then set out while the air temperature was between 39°C and 42°C (102°F–107°F). They would then “run up to the animal, which quickly flees, and track its footprints at a running pace. Meanwhile, the animal will have stopped to rest in the shade. The hunters must find the animal and chase it before it has rested long enough. This process is repeated until the animal is run to exhaustion.”
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Not all the hunters who began the hunt completed it, though the tracking skills of the older members of the group proved essential to success even when they did not keep up with the swiftest members. Hunts lasted approximately two to five hours, with an average running speed of 6.3 kilometers (about 4 miles) per hour, though the different hunters varied their speed. As Liebenberg points out, although this doesn’t sound very fast, the process involved carefully observing the animal’s movements and planning the approach—not simply head-down, ground-pounding forward motion.

The success rate of such persistence hunting is difficult to gauge, since so few hunts were recorded, but Liebenberg suggests that it may be about 80 percent, which compares very favorably with other hunting methods, such as hunting with clubs and spears or using dogs. The latter technique is the one that seems to have yielded the highest amount of meat per unit of effort, though again the number of documented hunts was relatively small. Such a success rate is also considerably higher than that obtained by mammalian predators such as lions or raptorial birds, which miss far more prey than they actually capture; one survey of raptors found that the birds managed to catch a meal only one out of five times.

After becoming infatuated with tracking and its effects on other parts of his life, Liebenberg developed software called CyberTracker designed to help record information from the environment in a user-friendly way, on handheld devices that can be taken into the field. The system can be used to monitor endangered wildlife, and Liebenberg even suggests its application to tracking criminals in remote areas. In a 2006 interview, he says, “With tracks and signs, you have to create hypothetical, causal connections between them, because you didn’t see what the animal did. You have to visualize what the animal did.”
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The increase in tracking skills with age and experience fits well with another observation about endurance running in humans: it is one of the only sports in which practitioners can improve with age and still compete effectively, well past the usual “prime” age of twenty to twenty-five. (Swimmers are said to hit their peak even earlier, at about age twenty-one.) In
Born to Run
, McDougall recounts a conversation with Bramble in which they calculated the decline of speed for marathon completion by men after the peak at age twenty-seven; the conclusion was that a sixty-four-year-old could run as well as a nineteen-year-old.
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Whether that is strictly true or not, many people continue to run marathon distances into their seventies, eighties, and even, for a few, their nineties. What’s more, women are extremely good at endurance running; in 2011, Amber Miller gave birth shortly after completing the Chicago Marathon, which is at least evidence that marathons are not something that only elite athletes with no other physically compromising conditions can master. Women also exhibit an extremely slow decline in their abilities. While these observations are not proof for the Endurance Running Hypothesis, they are certainly consistent with it.

To our prehistoric forebears, endurance running may also have been useful for obtaining food in another way besides hunting: scavenging carcasses that had either died of natural causes or been killed by other predators. Although the degree to which early hominins relied on such opportunities is debated by anthropologists, being able to outcompete either rival groups of humans or animals such as hyenas on their way to a fresh kill would obviously have been advantageous. Bramble and Lieberman point out that hyenas and wild dogs seem to detect their prey by smelling it or noting the circling of vultures overhead.
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While humans might have relatively poor senses of smell, the ability to reach a distant carcass quickly after seeing vultures at a distance could have given our ancestors an edge.

If humans evolved as long-distance runners, then, why do most of us moan at the suggestion of even walking a mile or two? Despite the popularity of running as exercise and the recent upsurge in marathon participation, few of us regularly log scores of miles a week. Certainly some people enjoy it; in
Born to Run
, McDougall rhapsodizes about the joy and ease of running long distances, particularly without shoes, about which I will have more to say later in the chapter.

McDougall talks about running the way foodies talk about a new source of heirloom tomatoes, or wine enthusiasts extol their favorite vintage. He is not really a fan of formally organized marathons, preferring trail runs with “no fees, no awards, no whining.”
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Yet even he acknowledges that the appeal is far from universal. The answer to the paradox, he and Bramble suggest, is that in addition to an ability to run far and well, we have urges that tell us to conserve our energy—urges that functioned beautifully when a certain amount of activity was inescapable. Reminiscent of Levine’s ideas about NEAT, the problem now is that we can easily give in to those urges, since we never have to go after that gazelle or compete with another tribe for a half-rotten carcass.

Our evolutionary exercise heritage may even suggest a way to fend off psychiatric disorders and Alzheimer’s disease. A protein called BDNF (brain-derived neurotrophic factor) is essential to proper functioning of the prefrontal cortex, a brain region that also is impaired with mental illness. The protein increases during exercise, and scientists Timothy Noakes and Michael Spedding suggest that if our ancestors had evolved as endurance runners, their levels of BDNF would also have increased. In turn, the protein would have become a key element in the further evolution of the human brain areas important in human attributes such as complex decision making, spatial mapping, and emotional control.
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Running down endurance

It should come as no surprise that the Endurance Running Hypothesis is not universally accepted. The proponents of the paleo lifestyle are, as I mentioned, often critical of the carbohydrates many runners eat to fuel their exercise. Some also scoff at the hypothesis itself. Mark Sisson is the author of
The Primal Blueprint
, as well as a website called
Mark’s Daily Apple
, which features a character called Grok, “an inclusive, non-gendered representative of all our beloved primal ancestors.” Grok purportedly would have spent his or her (but really, from later remarks, his) days “hunting game and gathering all manner of roots, shoots, seeds and fruits for both himself and his family/small band.”
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But apparently not running. Sisson says, “We did NOT evolve to run long distances. Sure, early humans were all-around fit enough and capable of the occasional long easy jaunt after an animal, but to think that natural selection redesigned our simian shapes to run the Boston Marathon is, in my opinion, ludicrous.”
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Taleb, the proponent of fear as the motivator for exercise, says, “Nobody in the Pleistocene jogged for forty-two minutes three days a week; lifted weights every Tuesday and Friday with a bullying (but otherwise nice) personal trainer, and played tennis at eleven on Saturday mornings . . . Marathon running is a modern abomination.”
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Among the main scholarly critics of the hypothesis are Henry Bunn from the Institute for Human Evolution at the University of the Witwatersrand in South Africa and Travis Pickering, an anthropologist at the University of Wisconsin. The two are in favor of the idea that increased ability to hunt and procure meat was instrumental in human evolution, but they are more skeptical about the importance, and feasibility, of persistence hunting by our ancestors.
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They argue that the kind of tracking essential to successful persistence hunting is most easily accomplished in dry, open areas with little vegetation, but these were not the habitats most common where early
Homo
lived. They also doubt that those impressive tracking skills even existed in the hominins of the time, with their smaller brains and presumably more limited cognition. Furthermore, they do not think that running was necessary to scavenge carcasses, pointing out that equally effective ways of getting to and monopolizing recently dead animals might have included “power scavenging,” or simply confronting a rival predator, human or otherwise, until it backed down.

Citing the foraging Hadza people of Tanzania, Bunn and Pickering say that while “they occasionally run toward perceived scavenging opportunities, the Hadza run more commonly to avoid approaching rain showers, stinging bees, and marauding elephants than to benefit any meat foraging by persistence hunting or scavenging.”
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The scientists also used the age and size of animal bones from archaeological sites, as well as the marks of tools on those bones, to deduce which individuals were selected as prey (old versus young, or large versus small) and how those prey were killed. They concluded that early humans were far more likely to have been ambush predators, like cheetahs, that lie in wait for prey and then kill it quickly, than either scavengers or persistence hunters.

Biologists Karen Steudel-Numbers and Cara Wall-Scheffler examined another assumption of the Endurance Running Hypothesis: the lack of a single optimal running speed in humans, which leads to an ability to adjust that speed for best exploitation of the prey.
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They measured the metabolic output of nine volunteers who ran on a treadmill at various speeds, and then did further calculations about how many calories would be expended in a persistence hunt of the distance Liebenberg had found to be the average in the Kalahari hunters. The runners turned out not to be as flexible in their use of energy at different speeds as the hypothesis supposes, and the energy consumption would have been considerable, meaning that early hunters would have needed to bring down a fairly large animal to make the effort worthwhile. Steudel-Numbers and Wall-Scheffler suggest that a mixture of walking and running might have made for a more efficient persistence hunt, particularly when water was at a premium.

Bramble, Lieberman, and their colleagues counter many of these objections, pointing out, for example, that just because modern hunters use sophisticated cognitive skills and have big brains does not mean that early hunters had to have the same qualities to be effective trackers; after all, mammals like the big cats can track quite well without a humanlike brain.
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And Lieberman’s most recent study, of the heel bones in Neandertals compared to those of
Homo sapiens
, led by David Raichlen and assisted by Hunter Armstrong, lends further support to human running as an adaptation.
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The fossil heels of ancient
Homo sapiens
, like those of modern people, had bones that allowed the Achilles tendon to become taut, while Neandertals had longer heel bones that would have been less energetically efficient during running. The efficiency of the shorter heel bones was further demonstrated by engaging volunteers to run on a treadmill while their oxygen consumption was recorded and then using an MRI scanner to measure the runners’ heel bones and Achilles tendons. The individuals who ran most efficiently also had shorter heel bones, suggesting that such bones evolved in humans as running became essential.