Hunter-Gatherers and Health - Part 7

Debunking the myths about sitting, sleeping, aging, and exercise

Up to now we've mainly focused on metabolism and diet. In this final entry we'll take a look at physical activity through the lens of hunter-gatherers by looking at Daniel E. Lieberman's book Exercised. Dr. Lieberman is a physical anthropologist and evolutionary biologist at Harvard University and was Herman Pontzer's thesis advisor. He has also worked extensively with the Hadza and other native peoples such as the Tarahumara.

In Exercised, Lieberman takes on a number of myths surrounding health and fitness from an evolutionary perspective: "The mantra of this book is that nothing about the biology of exercise makes sense except in light of evolution, and nothing about exercise as a behavior makes sense except in the light of anthropology." (xix)

The first myth is that what we refer to as exercise is something that we should naturally want to do. It's not. In fact, the opposite is true—it's a profoundly unnatural behavior. From an evolutionary standpoint, we're naturally inclined to rest, not to work out.

In our natural habitat calories were much harder to come by than they are today. Every calorie had to be painstakingly wrested from the surrounding countryside through laborious physical activity, whether chasing after animals or digging up tubers. As a consequence, wasting precious calories on activities not related to food procurement or reproductive success would have been a one-way ticket to extinction. We also descended from ape species who were much less active than we are on average.

Thus we evolved to be active but simultaneously to not want to expend energy on discretionary activities—what we now refer to as exercise. In fact, the word exercise originally meant ardruous physical labor like plowing a field—something we would want to avoid if possible. Later it came to mean, "to be harassed, vexed, or worried about something," hence the book’s title.

The bottom line is that humans evolved to acquire and expend much more energy than chimpanzees...by walking long distances, digging, sometimes running, processing our food, and sharing, we spend a lot more energy being active every day than chimpanzees, but that effort yields more calories that enable us to not only be more physically active but also to reproduce at about twice the rate.

The extra energy also enables us to have bigger brains, store more fat on our bodies, and do other good things. But there is a cost. The more calories we need, the more we are vulnerable to not having enough. Although the hunter-gatherer strategy is a boon to our reproductive success, it selects against wasting calories on discretionary physical activity. (E: 45)

My opinion is that while many animals are driven by deep instincts to move, sometimes causing pleasure, exercising as we define it—discretionary, planned activity for the sake of physical improvement—is a uniquely human behavior. (E: 21)

Therefore, Lieberman argues that we shouldn’t disparage people for not wanting to work out because it's a perfectly normal inclination from an evolutionary standpoint. Rather, it is those of us who are instinctively driven to work out (Lieberman calls them exercists) who are the outliers. The problem is that in our world we need to engage in voluntary physical activity if we wish to remain healthy, unlike our hunter-gatherer ancestors. They spent multiple hours every day engaged in physical labor not because they wanted to, but because they had to.

Lieberman is an enthusiastic proponent of the benefits of exercise, but he calls for compassion and understanding for those of us who are having a hard time trying to accomplish it rather than scolding and blame:

So let's banish the myth that resting, relaxing, taking it easy, or whatever you want to call inactivity is an unnatural, indolent absence of physical activity. Let's also refrain from stigmatizing anyone for being normal by avoiding physical exertion.

Unfortunately, we have a long way to go. According to a 2016 survey, three out of four Americans think obesity is caused by a lack of willpower to exercise and control appetite. Despite stereotypes of non-exercisers as lazy couch potatoes, it is deeply and profoundly normal to avoid unnecessarily wasting energy.

Rather than blame and shame each other for taking the escalator, we'd do better to recognize that our tendencies to avoid exertion are ancient instincts that make total sense from an evolutionary perspective. (E: 47)

In order to overcome our natural tendency to be lazy, he argues that we should strive to make exercise both necessary and fun. To that end, he recommends "nudges" and "shoves" to help make us more likely to work out, such as:

• Putting out exercise clothes the night before or sleeping in them.

• Setting a regular exercise schedule and using a friend or an app to remind you to exercise.

• Taking the stairs rather than an elevator or escalator and parking far away from an entrance.

• Exercising in a group context.

• Signing a binding commitment contract.

• Setting aside predetermined periods to exercise with friends who expect you to show up.

• Signing up for events that require you to train, especially where you pay money to participate.

Lieberman oddly does not mention walkable cities and neighborhoods (but I will). In many regions—Europe, for example—people can actually get around by walking. The United States is at the extreme other end of this spectrum, to the point where the built environment is expressly designed to prohibit people from walking even if they want to. The results of this are clear—there is less obesity and better overall health in European countries, even though walking burns relatively few calories. Of course, there's not much a single individual can do about this situation except move, which is not practical advice for most people.

Europeans (and other similar Old World cultures) are healthier overall because a certain amount of physical activity is built into their daily lives by design. In the U.S., we belittle Europeans for their small houses and public transportation while we sit in the drive thru in our oversized pickup trucks on the way to Walmart while guzzling a 24-ounce Faygo. Perhaps we should take a lesson. Lieberman’s insight tells us that the best way to ensure your long-term health is to structure your life in such a way that healthy habits are not a choice.

The Myth of the Athletic Savage

The high level of physical activity that people like hunter-gatherers engage in often gives the impression that they are all just naturally gifted superathletes, or somehow inherently physically superior to us because they lack technology and labor-saving devices.

A prime example are the Tarahumara Indians of the Copper Canyon in Mexico, among whom Lieberman has spent great deal of time over the years. This group is famous for their footraces in which they run epic distances through the hot, dry canyons of Mexico for up to fifty miles at a stretch. People like the Tarahumara give the impression that we too would be naturally able to perform superhuman feats like this if only we weren't spoiled by our modern conveniences.

Lieberman informs us that this notion is false. Taking a cue from the myth of the noble savage, he terms this, "the myth of the athletic savage:" "The myth of the athletic savage mistakenly suggests that humans uncorrupted by civilization can easily run ultramarathons, scale enormous mountains, and perform other seemingly superhuman feats without training." He argues that this notion actually dehumanizes native peoples, akin to the myth that African slaves did not experience pain, or that so-called "primitive" people did not think or feel the same way we do and therefore could be exploited at will.

The reality is that the people living in these societies have to engage in copious amounts of physical labor every single day as a basic condition of survival. This leads to a certain level of physical fitness even without "training," giving the erroneous impression that all “noncivilized” peoples are somehow natural born athletes. Instead, their abilities are just a natural outcome of their lifestyle. What we call "training" is just their everyday life—it’s not a discretionary activity that one must carve out time for or go to a separate place like the gym to engage in while wearing special clothing.

In addition, many of the reasons people in engage in strenuous physical activities in these societies are cultural rather than individualistic. These activities are built in to the fabric of their culture such that individual motivation is not required to the same degree as it is in ours:

The reason some Tarahumara run fifty miles or more on rare occasions is not much different from the reason Ironmen do triathlons: they think it is worth it.

However, whereas Ironmen subject themselves to full triathlons to test their limits (Anything is Possible!), Tarahumara run rarájiparis because it is a deeply spiritual ceremony that they consider a powerful form of prayer. Many Tarahumara I have interviewed say that the ball-game race makes them feel closer to the Creator. To them, chasing that unpredictable ball for mile upon mile is a sacred metaphor for the journey of life, and it induces a spiritual, trancelike state. It is also an important communal event that brings money and prestige.

Lastly, I think the rarájipari once had a vital practical function…it struck me that the ball game is a terrific way to learn how to track while running—an essential skill for the way the Tarahumara used to hunt deer on foot.

The myth of the athletic savage...trivializes the physical and psychological challenges faced by all athletes everywhere, the Tarahumara included. I have observed several rarájiparis and arivetes and seen how Tarahumara runners struggle just as much as the Ironmen of Kona to overcome cramps, nausea, bloody toes, and other forms of physical pain. They also suffer mentally and, like other athletes, draw strength from bystanders who urge them on.

It's time to discard one and for all ancient, insidious stereotypes about the physical superiority and virtuousness of people who don't grow up surrounded by laborsaving machines and other modern comforts. (E: 12-14)

Hunter-gatherers: they're just like us!

One traditional form of communal exercise done by people all over the world is dancing. Dancing is basically same activity as walking or running—hopping from one foot to the other. Every native society around the world has practiced some form of ritual dancing as an intrinsic part of their culture. Trance dances were used since prehistory to reinforce social bonds, and even as a form of ritual healing:

...imagine a world with no doctors, organized religion, television, radio, books, or any of the other institutions and inventions we depend on to minister to our physical and spiritual needs as well as entertain and educate us. Yet in every nonindustrial society ever studied, including the San, dancing helps people do these things and more...dances were not just enjoyable social gatherings that united everyone in the group but also important, frequent, and physically intense rituals that helped ward off evil and heal the sick...The San don't dance to get fit, but dancing all night once a week requires and develops phenomenal endurance.

Further, their dancing traditions are the rule, not the exception. I know of no nonindustrial culture in which men and women didn't dance for hours on a regular basis. The Hadza, for example, sometimes dance joyfully after dinner until the wee hours, doing line dances that involve some of the most sexually suggestive moves I have ever seen. On dark moonless nights the Hadza also perform the sacred epeme dance to heal social rifts and bring good hunting luck.

The Tarahumara have three or four different kinds of dances that often last between twelve and twenty-four hours and in some communities happen as much as thirty times per year...Even the famously repressed English used to dance much more than they do now. In Jame Austen's time, balls could go on all through the night. In Sense and Sensibility, Mr. Willoughby danced "from eight o'clock till four, without once sitting down…"

One rarely considered parallel between running and dancing is how both can induce altered states. Long periods of vigorous exercise stimulate mood-enhancing chemicals in the brain including opioids, endorphins, and, best of all, endocannabinoids (like the active compound in marijuana). The result is a runner's or dancer's high...The San believe there is great power in this half-conscious state, which frees the medicine men's spirits to communicate between this and other worlds, to draw out manifest sickness and as yet unrevealed ills, and to protect people from unseen but lurking dangers. (E: 221-223)

So those all-night raves turn out to have deep evolutionary roots. No wonder they call it trance music. Perhaps Zumba deserves more respect.

Sitting: Not the New Smoking

Another thing hunter-gatherers do a lot is sitting, often around a campfire. As we saw earlier, like all animals we are hard-wired to conserve energy as much as possible. Hunter-gatherers are no exception. To that end, they are not continually active from sunup to sundown, but spend a good amount of time sitting around resting and socializing just like everyone else. In fact, the amount of time they spend inactive isn’t all that different from those of us in industrial societies:

The typical Hadza adult spent nearly 10 of their waking hours without having any detectable motion. That's more than the Netherlands and US, which are closer to nine hours, and over a full hour more of sedentary time than the average Australian.

The Hadza had, on average, somewhat longer stretches of inactivity and made more transitions between upright and resting than Europeans, but there was a lot of variation among individuals, so these latter differences weren't statistically significant.

Modern hunter-gatherers are just as sedentary as we are (Ars Technica)

Why then, Lieberman asks, is sitting considered to be so extremely unhealthy—even potentially deadly—for us? A number of studies have correlated high amounts of sitting with a whole raft of pathological conditions, and it's even been associated with premature death! The press is full of alarmist stories about how "sitting is the new smoking." Yet smoking is a profoundly unnatural activity; sitting is not. To paraphrase a statement from earlier in this series: "Is mother nature a psychopath? Why would she deliberately design a normal daily activity to shorten the lifespan of the human race?"

Lieberman fortunately sheds some much-needed light on this issue. Sitting is not the new smoking, he assures us. It's yet another myth. Hunter-gatherers demonstrate that it's not the number of hours sitting per day that's bad for us. Rather it's the way we sit in Western societies that can be harmful for us.

The first problem is that we tend to sit for long, uninterrupted stretches of time. While hunter-gatherers do spend a decent amount of time sitting, it is parceled throughout their day rather than a single block like with our "desk jobs." Instead, periods of inactivity are interspersed with periods of light, moderate, and even vigorous physical activity. There seems to be something about sitting for long uninterrupted stretches of time that encourages inflammation. By interrupting long periods of sitting with frequent breaks we mitigate some the bad effects of sitting and make it more similar to what hunter-gatherers do.

The other factor is that hunter-gatherers are more likely to squat or kneel than sit in a chair. For most of human history, people have squatted, knelt or sat on the ground¹. The Hadza spend about 30 per cent of their "inactive" time in a squat or kneel. Stress marks on bones indicate that squatting has been a regular human activity for millions of years: "Because squatting creates tiny smoothed regions on ankle bones known as squatting facets, we can see that humans for millions of years, including Homo erectus and Neanderthals, regularly squatted." Even in farming cultures people usually sat on wooden stools and benches most of the time rather than in chairs with backs. Chairs as we know them are fairly recent².

Sitting in seats without backs engages our core muscles to keep us upright and stable. We cannot slouch or go limp the way we can when sitting in a chair. Squatting also engages leg muscles such as the calves and thigh. These large muscles in the leg utilize a good portion of our blood sugar intake. By keeping them engaged while squatting we more effectively regulate glucose metabolism. When these muscles are inactive that sugar can remain in our bloodstream for longer periods of time where it can cause more damage.

Hadza adults...accumulate the same amount of resting time as Westerners do during the day, hanging around in camp or resting on a foray. But in the industrialized world, we spend far too much of our lives in comfy chairs and sofas that leave our muscles limp. Hadza men and women use more active resting postures, like squatting, that engage the core leg muscles. That low level of muscle activity helps reduce circulating levels of glucose, cholesterol, and triglycerides. (B: 251-252)

All in all, assuming that what hunter-gatherers do is evolutionarily "normal," then comprehensive studies of contemporary foraging populations from Africa, Asia, and the Americas indicate that a typical human workday used to be about seven hours, with much of that time spent on light activities and at most an hour of vigorous activity.

To be sure, there is variation from group to group and from season to season, and there is no such thing as vacation or retirement, but most hunter-gatherers engage in modest levels of physical effort, much of it accomplished while sitting. (E: 18)

Also there is the simple fact that in industrialized cultures any time we are not physically active we are typically sitting. That's another reason why sitting is so closely correlated with bad health outcomes—it's not the activity itself is somehow harmful to us the way that smoking is. Sitting for us usually equates to time not spent exercising—something that is not the case with hunter-gatherers. And if being inactive were inherently bad for us, then why is sleeping not considered harmful as well?

Sleeping: Not Eight Hours

Another normal activity that people in industrial societies frequently struggle with is sleeping. We're told we must get at least eight hours of uninterrupted sleep every night—or else. Breathless news stories assure us that not getting enough sleep—just like sitting too much—is tantamount to digging our own grave.

Given that hunter-gatherers live in environments free from electric lights, Netflix, and alarm clocks, we would surely expect them to get their eight hours, right? But it turns out that the eight hour requirement is a myth.

Just like with diet and exercise, researchers have studied hunter-gatherer sleeping patterns. What they found was there was no natural length of time, nor any specific set of hours, that people slept. Other than the fact that people tend to sleep when it's dark and are mostly active during the day, there was no clear pattern:

The most electrifying study by far was by the UCLA sleep researcher Jerome Siegel and his colleagues, who affixed wearable sensors to ten Hadza hunter-gatherers from Tanzania, thirty San forager-farmers from the Kalahari desert, and fifty-four hunter-farmers from the Amazon rain forest in Bolivia. None of these populations have electric lights, let alone clocks or internet access. Yet to Siegel's astonishment, they slept less than industrialized people did.

In warmer months, these foragers slept on average 5.7 to 6.5 hours a day, and during colder months they slept on average 6.6 to 7.1 hours a night. In addition, they rarely napped. Studies that monitored Amish farmers who shun electricity as well as other nonindustrial populations such as rural Haitians and subsistence farmers in Madagascar report similar average sleep durations, about 6.5 to 7.0 hours a day.

What's more, when you look closely, there is little empirical evidence that average sleep duration in the industrial world has decreased in the last fifty years. The more we look, the less we can profess eight hours to be normal. (E: 81-82)

Even studies of people living in contemporary societies don't show that eight hours of sleep is necessary. Instead, they find that too much sleep can be just as harmful as too little. Studies indicate that the ideal amount of sleep is actually closer to seven hours. People who slept more than eight hours a night actually had an increased chance of dying compared to those who slept less:

...a massive study by Daniel Kripke and colleagues...examined the health records and sleep patterns of more than one million Americans. According to these data, Americans who slept eight hours a night had 12 percent higher death rates than those who slept six and a half to seven and a half hours. In addition, heavy sleepers who reported more than eight and a half hours and light sleepers who reported less than four hours had 15 percent higher death rates.

Critics pounced on the study's flaws: the sleep data were self reported; people who sleep a lot may already be sick; correlation is not causation. Yet since then, numerous studies using better data and sophisticated methods to correct for factors like age, illness, and income have confirmed that people who sleep about seven hours tend to live longer than those who sleep more or less. In no study is eight hours optimal, and in most of the studies people who got more than seven hours had shorter life spans than those who got less than seven hours. (E: 82)

Just like with sitting, what is unnatural about sleep is not so much the length of time, but rather they way we do it. We try as much as possible to sleep alone on soft cushions in a deathly quiet, dark, and temperature-controlled atmosphere. This has been called the "lie down and die" model of sleeping because it resembles lying in a coffin. But that's not how humans slept for the vast majority of our existence! Rather, "We evolved to sleep communally in chaotic noisy contexts." (E: 88) Paradoxically, the “lie down and die” model may be actually making it harder for us to fall asleep:

As a rule, foragers sleep in conditions that border on bedlam. People sleep in groups usually near a fire in relatively busy environments with no barriers to block out noise or light...To modern sensibilities, the chaos of Stone Age sleeping conditions seems antithetical to a good night's rest, but the anthropologist Carol Worthman has proposed that the reverse may be true.

As we go through the initial stages of NRAM sleep, we become gradually less aware of our environment. This progressive tuning out may be adaptive because our brain is monitoring the world around us as we fall asleep, possibly to assess whether it is dangerous to sleep. Slowly receding perceptions of nearby friends and family talking, a crackling fire, infants crying, and the fact that those hyenas are far away signal to the brain that it is safe to enter a deeper, unconscious stage of sleep. Ironically, by insulating ourselves so effectively from these comforting stimuli, we may be making ourselves more prone to becoming stressed about sleep. (E: 86)

And the idea that we are supposed to sleep continuously through the night without interruption has also been called into question. A couple of researchers claimed to have found evidence that people everywhere in the past used to have "biphasic" sleep patterns where sleep was divided into two segments. In between these periods people would get up in the middle of the night and do whatever activity was most convenient. Although they claimed that this pattern was more-or-less universal in preindustrial societies, it instead seems to be culturally determined. Nevertheless, it has been found that some cultures do indeed engage in segmented sleep:

Debate over the normality of [sleeping] patterns was triggered by the anthropologist Carol Worthman and the historian Roger Ekrich. These scholars argued that it was normal prior to the Industrial Revolution for people to wake up for an hour or so in the middle of the night before going back to sleep. In between "first sleep" and "second sleep," people talk, work, have sex, or pray. By implication, electric lights and other industrial inventions might have altered our sleep patterns.

However, sensor-based studies of nonindustrial populations reveal a more complex picture. Whereas most foragers in Tanzania, Botswana, and Bolivia sleep through the night, subsistence farmers in Madagascar often divide their sleep into first and second segments. In truth, most biological phenomena are highly variable, and sleep is no exception. (E: 83)

The forgotten medieval habit of 'two sleeps' (BBC Future)

Another unnatural phenomenon is forcing all of us into the same sleeping pattern in terms of the hours in which we sleep—that is, the time we go to bed and wake up set by the clock. We have artificial set sleeping hours that we're all expected to follow. Industrial capitalist societies gang-press everyone into an early-bird regime. Waking up early is considered the height of virtue and discipline—admiring stories abound of people hitting the gym at 4:30 AM, or heroic CEOs who are in their office before dawn every morning. By contrast, people whose natural inclination is to go to bed and wake up later are universally derided as "lazy" and have all sorts of negative personal and professional outcomes.

But in tribal societies people are naturally divided into "larks" and "owls." It's thought that these staggered sleeping patterns developed to ensure that someone in the group was awake and alert at all times in order to defend against potential threats. The fact that people tend to sleep less as they age may also be an outcome of this requirement:

When the anthropologist David Samson measured sleep activity in a camp of twenty-two Hadza hunter-gatherers for twenty days, he found so much variation in terms of who was asleep at different times that he estimated that at least one person in the camp was awake for all but eighteen minutes per night.

From an evolutionary perspective, such variation is probably adaptive because we are most vulnerable when asleep in the dangerous night. Having at least one alert sentinel, often an older individual, would have reduced the dangers of sleep in a world full of leopards, lions, and other humans who wish us harm. (E: 83)

Another highly unnatural habit in modern societies is parents and children sleeping in separate rooms. For all of human history co-sleeping was the norm, even in peasant farming societies. Ours is the first to isolate babies in cold, dark rooms and to deliberately ignore their desperate pleas for reassurance and comforting—in other words, to let them "cry it out." Is it any wonder our society tends to produce so many psychologically damaged individuals?

I can think of no peculiarity of modern sleeping culture that more counterproductively promotes privacy at the expense of stress than banishing children from beds and bedrooms. In every culture until recently, infants slept with their mothers. Many cultures consider not sleeping with your child a form of child abuse...Co-sleeping not only helps mothers and infants sleep better; it helps mothers and infants coordinate their sleeping and feeding and provides a wealth of positive, nurturing interactions. (E: 88-89)

The Way We Walk

Walking is the quintessential human activity. It's literally what we evolved to do. Habitual, obligatory, bipedal locomotion is the most distinctive trait of our particular branch of the primate family tree. It's what distinguishes the genus Homo from earlier tree-climbing ape species even before brain growth, fire, carnivory, or tool use.

Therefore it makes sense that the most common physical activity that hunter-gatherers do is walk. A lot.

If there is one physical activity that most fundamentally illustrates the central point of this book—that we didn't evolve to exercise but instead to be physically active when necessary—it is walking. Average hunter-gatherer men and women (Hadza included) walk about nine and six miles a day, respectively, not for health and fitness but to survive. Every year the average hunter-gatherer walks the distance from New York to Los Angeles. Humans are endurance walkers. (E: 173)

Pontzer tells a story in Burn about following the Hadza around on their daily routine. As an anthropologist, he was instructed to speak into a recorder every five minutes describing what the Hadza were up to. He found himself repeating "walking... walking... walking…" into the recorder over and over again like some sort of broken record. Upon returning to the camp, one of the other anthropologists took him aside and informed him that this was not necessary. The default activity for a Hadza person is walking, therefore it's simply assumed that walking is what they are doing unless noted otherwise:

Brian [Wood] explained how he did it: any time a five-minute check-in was skipped in the notes, it could be assumed that you were walking. Walking was the default activity, like breathing. It didn't hurt to note when someone was doing it, but it was much more important and useful to note when they stopped. To a seasoned field guy like Brian, the logic was obvious.

"When you're out with the Hadza, you're always walking." (B: 73)

The problem with walking as a form of exercise, however, is that we're too good at it. Walking evolved as the most energetically efficient form of locomotion allowing humans to cover long distances in search of food and prey in the grasslands of Africa. Because of this we expend very little energy walking compared to other activities like running, swimming or climbing.

While ten thousand steps a day has entered into the popular imagination as a goal to strive for, it turns out that—like the 2,000 calorie diet and sleeping eight hours a night—it's not based on any scientific evidence but was rather a marketing ploy by a pedometer company:

In the mid-1960s, a Japanese company, Yamasa Tokei, invented a simple, inexpensive pedometer that measures how many step you take. They company decided to call the gadget Manpo-kei, which means "ten-thousand-step-meter," because it sounded auspicious and catchy. And it was. The pedometer sold like hotcakes, and ten thousand steps has since been adopted worldwide as a benchmark for minimal daily physical activity. (E: 193)

Despite its dubious origins, Lieberman still sees 10,000 steps per day as a decent goal to strive for. It’s enough to push us out of the “sedentary” category. In contrast to Pontzer, Lieberman argues that walking can indeed help us to lose weight if we manage to do enough of it:

...because walking is so energy efficient, it takes months or years for small doses of exercise to add up to substantial weight losses. But it's possible. Just as the daily four dollar cup of coffee adds up to nearly fifteen hundred dollars a year, someone who manages to talk an hour a day without compensating by eating more calories could theoretically lose an impressive forty pounds in two years. (E: 191)

Running is also an activity that we have evolved to do. Lieberman is perhaps most famous for co-developing with Dennis Bramble the "Running Man" hypothesis—the idea that humans initially evolved bipedal locomation as way of hunting prey by pursuing it to exhaustion. This method predated tool use and may have even helped facilitate the expanding brains that made subsequent tool use and big game hunting possible. Lieberman and Bramble extensively documented all of the anatomical changes in human physiology that took place from head to toe which make us uniquely adapted to long-distance running.

In addition to being able to run long distances relatively fast, humans are unusual in habitually running long distances in the the first place. Have you ever seen a wild animal run several miles on its own for no apparent reason? With the exception of social carnivores like wolves, dogs, and hyenas which run up to ten miles to hunt, few animals willingly run more than a hundred yards or so without being forced to. (E: 205)

Running has all sort of clear physiological benefits, probably due to its deep evolutionary legacy. Why then, if we truly were “Born to Run,” does it slowly wear down and destroy the cartilage in our ligaments and knees?

It turns out that it doesn't. Lieberman tells us that the idea that running inevitably destroys your knees is yet another myth:

Despite what many doctors and others assume, more than a dozen careful studies show that nonprofessional runners are no more likely to develop osteoarthritis than non-runners. In fact, running and other forms of physical activity help promote healthy cartilage and may protect against the disease.

A study from my lab showed that people's chances of getting knee osteoarthritis at a given age and weight have doubled over the last two generations as we have become less, not more active. (E: 216)

Why, then, do we hear about so many injuries from running?

One reason is that hunter-gatherers run and walk daily throughout their entire lives, building up the tendons and muscles required for healthy running. By contrast, in today’s world many people take up running after being sedentary for a long time. This means that certain parts of their bodies have not had sufficient time to adapt to the rigors of running, leading to injuries. This is especially true if we push ourselves too hard in the beginning:

The problem is that connective tissues like bones, ligaments, and tendons adapt considerably more slowly than muscles and stamina. Novice runners, especially first-time marathoners, risk injury because they can increase their mileage or speed (or both) faster than their shins, toe bones, Achilles tendons, IT bands, and other vulnerable tissues can adapt. Many experts thus advocate increasing mileage only 10 percent a week. (E: 217)

Another is the fact that hunter-gatherers don't run on paved surfaces and usually run barefoot or with minimal footwear. Hard surfaces increase the impact stresses on the bones and joints. Athletic footwear prevents the body from receiving the necessary feedback from the feet and legs which naturally forces us into a more ergonomic running posture that prevent injuries.

Finally, running is usually a group activity in hunter-gatherer societies, probably the same as it was for our remote ancestors. Hunter-gatherers consider proper running technique to be a learned skill, just like hunting itself. They are able to learn proper form and technique by emulating the more experienced runners in the group which helps keep them injury-free.

When I ask runners from different cultures if there is a best way to run, they invariably tell me they consider running a learned skill...Tarahumara runners tell me they learn to run properly by following champions of the ball game races. Kenyan runners do the same, often honing their skills in groups...

Watch ten Americans training and you'll generally see ten different running styles, but a group of Kenyans often looks more like a flock of birds with the leader not just setting the pace but also modeling how to run so that the runners appear to move in unison, adopting the same cadence, arm carriage, and graceful kick. (E: 218-219)

Lieberman offers the following advice to those of us trying to do more running in modern societies:

1) Avoid overstriding. Get your knees up when you swing your legs forward so you land vertically with the foot below the knee.

2.) Taking 170-180 steps per minute, regardless of speed. Increase speed by widening your stride rather than taking more steps.

3.) Don’t lean forward too much at the waist. Too much leaning encourages overstriding.

4.) Land gently with a nearly horizontal foot. Land on the ball of the foot before letting down the heel. (pp. 219-220)

Any amount of running linked to significantly lower risk of early death (Science Daily)

Aging and Death

Most animals don't live very long past their prime reproductive years. They enter what's been called "the shadow of natural selection."

Humans are an exception to this rule. We live a long time beyond our prime reproductive years, unlike most other animals and even close relatives like chimps and bonobos. Why is that?

One reason is because the foraging lifestyle means that humans can continue to bring home surplus calories long after their reproductive years have passed, and the fact the we share our food means that those calories benefit the whole group. In fact, in hunter-gatherer societies like the Hadza, grandmothers are actually more active than their nursing daughters. Hence the trend for longer lifespans has been dubbed the grandmother hypothesis. The idea is that by surviving into old age, grandparents could continue provisioning and looking after their offspring. Natural selection therefore favored individuals who lived long enough to be able to provide assistance to their children and grandchildren which allowed them to have more surviving descendants.

This also explains how humans are able to reproduce so much faster than other apes. A chimp mother can only forage enough food for herself and a single offspring, thus she has to wait until her child is grown and can forage for himself or herself before she can have another baby—around four to five years.

But in human groups based on foraging and sharing, other relatives—including older ones—can help feed and look after the young children. This allows mothers to have more of them without having to wait for the earlier ones to become independent permitting offspring to be spaced closer together—a difference that adds up over time. We think of this just as normal behavior, but in fact it's highly unusual in the animal kingdom.

Also, in human cultures social learning is paramount. We pass down accumulated knowledge to subsequent generations, and this knowledge is absolutely essential for our survival—to a greater degree than even raw intelligence or cooperation. Therefore having elderly around who could serve as repositories for knowledge and wisdom was more beneficial for human groups than for other animals.

Anthropologists have shown that grandmothers, grandfathers, aunts, uncles, and other older individuals in foraging populations from Australia to South America remain active throughout life, gathering and hunting more calories every day than they consume, which they provide to younger generations. This surplus food helps provide other calories to children, grandchildren, nieces and nephews and reduces how much work mothers have to do.

Elderly hunter-gatherers also help younger generations by contributing knowledge, wisdom, and skills for about two to three decades beyond childbearing years. Contrary to the notion that hunter-gatherers die young, foragers who survive the precarious first few years of infancy are most likely to live to be sixty-eight to seventy-eight years old. That's not far off from the life expectancy in the United States, which is currently between seventy-six and eighty-one. (E: 230)

Because it was not just the existence of grandparents but active grandparents that was beneficial for offspring, Lieberman sees this as the reason why exercise is so effective at warding off the most severe effects of aging. Exercising turns on all sorts of physiological repair mechanisms to help us live longer and healthier lives. He calls this the active grandparent hypothesis. By this reasoning, we are not naturally designed to become less active as we age. Rather, it is inactivity that accelerates the deleterious effects of the aging process, not too much physical activity:

Although elderly hunter-gatherers are afforded great respect, those who can't walk long distances, dig tubers, collect honey, and schlep stuff home presumably become burdens when food is limited. It follows that if humans were selected to live long after we stopped having babies, we were probably not selected to live those years in a state of chronic disability.

From a Darwinian perspective, the best strategy is to live long and actively and then die fast when you become inactive. An even better strategy, however, would be to avoid any deterioration with age in the first place. (E: 234)

Assuming that this thesis is correct, it’s a myth that chronic diseases are just a natural outcome of old age.

To make this point, Lieberman helpfully distinguishes between lifespan and healthspan. Lifespan is the number that ultimately winds up on the death certificate. Healthspan is the number of years of robust physical health that we enjoy during our lifetime. For hunter-gatherers, lifespan and healthspan basically coincide: "two thirds of older hunter-gatherers remain at functional capacity with limited morbidity until just before death, which most often occurs in the seventh decade. Accordingly, their health span and life span are very similar..."

In industrialized societies, by contrast, this is not the case. Lifespan and healthspan are diverging ever more in modern societies. More and more people today live with chronic illnesses and suffer with adverse health conditions for a long time before they finally croak, drastically undermining their quality of life.

It’s often argued that people simply didn't live long enough to get these problems in the past. But once again, as we saw above that’s simply not true. Hunter-gatherers did not live only until around forty, rather they lived nearly as long as we do without suffering with the sorts of chronic health conditions that are endemic in our society. These diseases, then, are not the inevitable consequence of aging but are caused by our modern lifestyle including exercise and diet:

This shift, in which more of us live longer but die from chronic rather than infectious diseases, thus extending morbidity, is known as the epidemiological transition and is widely hailed as medical progress. By not dying rapidly from smallpox in our youth, aren't we fortunate to die slowly from heart disease at an older age?

The thinking is mistaken. My last book...made the case that many of the diseases that kill us slowly today are mismatch diseases caused by our bodies being imperfectly or inadequately adapted to modern environmental conditions like smoking, obesity, and physical inactivity.

Although these diseases are commonly classified as diseases of aging because they tend to arise when we are middle aged, they are not caused by age, nor should they be considered inevitable consequences of aging. Plenty of people live to old age without getting these diseases, which rarely if ever afflict elderly hunter-gatherers and many ages people who live in subsidence societies. If many so-called diseases of aging are preventable, it follows that a slow demise at the end of life is not inevitable. (E: 245-247)

What Kind and How Much?

So, based on everything we've learned, how much should we exercise to be like hunter-gatherers?

Lieberman explicitly denies that there is any optimal dose or type of exercise. Nevertheless, based on the current medical research, he advises:

In the final analysis, exercising a minimum of 150 minutes per week is a good prescription as any and has the advantage of being a clear, attainable dose. But there is no optimal, most beneficial dose of exercise. People who exercise the least have the most to gain from just modest added effort, more is better and the benefits of additional exercise gradually tail off. (E: 285)

He recommends a combination of aerobic activity with some strength training, but to especially focus on aerobic activities because of their demonstrated health and anti-aging benefits. Of course, running is big part of that. He is also very complementary towards what's known as High Intensity Interval Training, or HIIT. This combination of aerobic activity with short bursts of maximum all-out effort seems to provide clear physiological benefits and mimics the kinds of activities our hunter-gatherer ancestors would have engaged in, as he illustrates using an old documentary:

In the extraordinary 1957 documentary The Hunters, John Marshall followed and filmed a group of desperately hungry San hunters in the Kalahari who were having no luck hunting until they encountered a herd of giraffes. In a riveting scene, one of the hunters dashed full speed, barefoot, for about a minute through the grass after the giraffes in order to get a decent shot with a poison-tipped arrow.

His shot succeeds, but he and his companions must track the wounded and poisoned giraffe for more than thirty miles as the suffering giraffe tries to flee. The initial sprint illustrates unforgettably how occasional sort bursts of high intensity were vitally important complements to more usual low- to moderate-intensity aerobic activities... (E: 294)

…After they finally killed [the] giraffe, they had to butcher it, but giraffes are heavy. The film shows how strenuously they labor to cut the enormous animal into pieces, remove its thick skin, and then carry hundreds of pounds of meat. Other common resistance exercises in the Stone Age included digging and climbing.³ (E: 296)

Fortunately, we don't have to hoist giraffe carcasses like the San or run fifty miles at a stretch like the the Tarahumara in order to replicate the exercise habits of the average hunter-gatherer. Activity levels approaching those of the Hadza are fully achievable even for those of us living in sedentary industrial societies: “if you are a typical person who barely exercises, it would take you just an hour or two of walking per day to be as physically active as a hunter-gatherer." (E: 19)

Hunting and gathering is hard work, but it's not the Tour De France. Our research with the Hadza shows that men and women rack up about five hours of physical activity each day. A third of that—around one to two hours—is what physiologists call "moderate and vigorous" activity like fast walking or digging tubers, the kind of exertion that really gets your heart rate up. The rest is "light" activity, like strolling around camp or picking berries. Daily workloads for groups like the Tsimane and Shuar are similar.

Living hunter-gatherers and other small-scale societies are culturally diverse, of course, but it's reasonable to take five hours of physical activity, with one or two hours in the "moderate" or "vigorous" range, as a reasonable guideline for the amount of physical activity our hunter-gatherer ancestors typically got each day. If we want to think of this in terms of steps per day, we'd be well north of 10,000. Hadza men and women average around 16,000 steps per day. (B: 249)

At first pass, then, we might aim to be on our feet for around five hours a day, with an hour or so of structured exercise or other activity where we get our heart rates up...With a little luck, we'll grow old with strong hearts, fresh legs, and clear minds. Healthy as a Hadza. (B:250)

We should intersperse light or moderate activities with more vigorous activities, but we don't have to overdo it or go full out for hours every day to get the benefits. Normal activities can fit the bill just fine:

Vigorous activity, defined as anything demanding 6 METS or more, has positive effects all over the body. These are activities like jogging, playing soccer or basketball, backpacking, or bicycling that really get your heart rate up. Vigorous exercise gets the blood rushing through your arteries, triggering the release of nitrous oxide, which keep them open and elastic.

Pliable vessels keep blood pressure low and are less likely to clog or burst, the catastrophes that cause heart attacks and strokes. Moderate activity (3 to 6 METS, things like a brisk walk, and easy bike ride, or gardening) is great too, It helps with the trafficking of glucose out of the blood and into the cells, and it is known to improve mood, stress, and can even help treat depression.

Is there such a thing a too much exercise? It turns out that there is—it's when we are burning so much energy relative to our intake that the body has trouble keeping up with basic metabolic maintenance tasks which manifests itself as "overtraining syndrome." In this case, the immune system may be suppressed, resulting in things like colds that won't go away or injuries taking longer to heal. Pontzer has shown that the limit of human endurance is around 2.5 times the body’s resting metabolic rate, or about 4,000 calories a day for the average person. He has found that our endurance is not limited by our muscular output, but rather by the amount of calories our digestive systems can extract from food in the long term.

But, of course, only the professional athletes among us are likely to come anywhere close to those levels of physical activity. For the rest of us normal humans, both Pontzer's and Lieberman’s prescription for exercise is simply: more is better.

So how much exrcise is best? More is the simple answer. The vast majority of us are far too chimpanzee-like in our daily activity, burning too many calories on nonessential (and potentially harmful) tasks like inflammation instead of exercise. Unless you're already pushing your physical limits on a regular basis, you really can't go wrong spending more time in motion, and your body will thank you. We should be cognizant of our inactive behavior as well, avoiding long periods of sitting in chairs and aiming to keep a regular sleep routine. And if you're one of he few who already spend hours exercising each day, look out for the warning signs of overtraining, like constant fatigue or colds that won't go away. (B: 252)

In the spirit of Michael Pollan's famous dictum: "eat food; not too much; mostly plants," Lieberman offers his own summary advice regarding exercise: "make exercise necessary and fun; exercise several hours a week, mostly cardio but also some weights; some is better than none; and keep it up as you age." (E: 297).

That's the end of this series! The BBC created a great short film featuring both Lieberman and Pontzer covering a lot of the information we’ve talked about. It’s not on YouTube so I can’t embed it, but you can watch it here: How exercising doesn't mean you burn calories.

1. Squatting is also the natural posture to take a dump. It's understood that our bowels are more fully evacuated in this posture rather than sitting on the porcelain throne, hence the benefits of squatting toilets. Regular squatting also keeps your legs strong and supple as you age, which unfortunately declines precipitously in cultures where people sit mostly on furniture.

2. "One place where people did not often sit was in chairs. The Pharaonic Egyptians had used chairs, and the ancient Greeks refined them to elegant and comfortable perfection in the fifth century B.C. The Romans introduced them to Europe, but after the collapse of their empire—during the so-called Dark Ages—the chair was forgotten. Its reappearance is difficult to pinpoint, but by the fifteenth century, chairs started to be used again. But what a different chair! The Greek klismos had a low, concave backrest that was shaped to the human body, and splayed legs that allowed the sitter to lean back. The comfortable posture of a lounging Greek, with his arm bent casually over the low chair back and his legs crossed, is recognizably modern. No such position was possible in a medieval chair, which had a hard, flat seat and a tall, straight back whose function was more decorative than ergonomic. During the Middle Ages, chairs—even the boxlike armchairs—were not intended to be comfortable; they were symbols of authority. You had to be important to sit down in a chair--unimportant people sat on benches. As one historian put it, if you were entitled to a chair you sat up in it: nobody ever sat back." Witold Rybczynski, Home: A Short History of an Idea, page 26.

3. You can watch this documentary on Archive.org:

https://archive.org/details/huntersfilmpart1

https://archive.org/details/huntersfilmpart2