Harvard professor Daniel Lieberman is one of the world's leading experts on the human body, and kick-started the cult of ultra long-distance running. Which makes it all the more surprising that he now says that we were born to be lazy. Rhys Blakely finds out more.
Daniel Lieberman has just returned from his morning run when we meet via Zoom, which means that his cells will be undergoing the "afterburn". The term is used to describe a heightened metabolic state that can endure for hours after physical exertion. Dozens of repair mechanisms are said to kick in, at a microscopic level, to reverse some of the biological damage that accumulates with age. As he sits in his home office in Cambridge, Massachusetts, it seems fitting that Lieberman, a lithe 56-year-old Harvard professor and avid marathon runner with a resting heartbeat in the forties, should be found in this restorative condition.
Over the past two decades, few academics have done more to shape the way the western world views athleticism. Lieberman studies how and why the human body is the way it is. His research has combined paleontology, anatomy, anthropology and experimental biomechanics and today he's best known for his work explaining how we came to run.
A paper he co-authored in 2004 – Endurance Running and the Evolution of Homo – proposed that early humans prospered because they developed an ability to cover fantastically long distances more efficiently than rival species. His ideas would become massively influential, providing a jolt of new energy to the cult of ultra long-distance racing. The barefoot running craze was built on experiments by Lieberman and his colleagues, which suggested that foregoing trainers could improve an athlete's gait.
Along the way, Lieberman decided that he couldn't study running without participating. He became, he'll admit, mildly obsessive and he now competes in the Boston marathon every year. He can finish it in a respectable 3 hours 30 minutes. "Today was sort of a recovery run – five miles (8km)," he tells me.
All of which makes the message of his new book something of a surprise. We were born to be lazy, it argues, and exercise is entirely unnatural. Those who peddle it as a panacea should be viewed with suspicion.
The elite athletes that the sports industry promotes as paragons of human achievement often make poor biological role models, he says. A host of unhelpful myths have sprouted that distort discussions of physical activity and health. The idea that you need eight hours' sleep a night? It's nonsense.
The notion that sitting is intrinsically unhealthy? Not really. The idea that humans in their primal state were strapping, buff specimens built for ambushing mammoths? Nope. The rule that to shed weight one must exercise? It depends.
If exercise really is a "magic pill" that will cure or prevent most diseases, then why, Lieberman asks, are more people living longer than ever, despite being more physically inactive than ever?
"We oversimplify things, and biological problems aren't simple – and the result is that people become distrustful of science," he says. We are bombarded with conflicting inaccuracies on how to stay fit. People are confused and feel embarrassed and they hate being nagged – I mean, I'll tell you: my family hates being nagged to exercise."
He'd like to set us on a new footing, based on a better understanding of how our bodies came to be. He pauses and looks at me through the prism of Zoom. "For me," he says, "the biggest myth is that we evolved to exercise in the first place."
The first plank of his argument is this: as we wrestle with how to be healthy, we should acknowledge our evolutionary backstory. This means recognising how, for millions of years, it paid to dodge physical activity wherever possible. The invisible laws of natural selection, he wants us to realise, do not care whether or not we lead happy lives. They are oblivious to whether we enjoy fruitful retirements and avoid bad backs and creaky knees caused by morbid obesity. All that matters is that we pass on our genes. "Life is really a very simple equation," he says. "Energy in; babies out."
Westerners who guzzle cheap junk-food calories are acting on ancient Stone Age impulses.
At this primal level, success means surviving long enough to create offspring who can fend for themselves. And for aeons, the secret to making it that far was being as inactive as possible. Calories were scarce in the Stone Age. Funnelling energy into processes that did not somehow support reproduction – including what we now know as recreational exercise – made no sense.
As Lieberman sees it, westerners who loaf and guzzle cheap junk-food calories are acting on these ancient impulses. "Hunter-gatherers don't exercise," he says – by which he means that they never burn calories purely in the name of staying fit. "They're physically active – but they'd be just like us if you put them in our world."
So if we were born to run, we were also built to be lazy. As Lieberman sees it, admonishing people for not exercising makes no sense. Our species evolved to conserve energy wherever possible. Why besmirch somebody who would rather sit on the couch than go for a jog? "That's normal and you're not lazy and there's nothing wrong with you. We should stop shaming and blaming people."
We should also be vigilant against hyperbole. Take the idea that "sitting is the new smoking". One American professor of medicine at a top-class research institute has warned that chairs are "out to get us, harm us, kill us" and that "for every hour we sit, two hours of our lives walk away – lost for ever".
It's not true, says Lieberman – or, at least, the truth is more complicated. Sitting is an ancient pastime and entirely natural, though chairs are, admittedly, a very recent invention. "If our ancestors from generations ago behaved like today's hunter-gatherers and farmers, then they likely sat for five to ten hours a day, as much as some but not all contemporary Americans and Europeans," he writes in his new book, Exercised: The Science of Physical Activity, Rest and Health.
So vilifying sitting makes little sense. Studies find that westerners with desk jobs tend to live longer than manual workers, who are on their feet for longer. And standing desks are not automatically a healthier option – the marketing that pushes them "deceptively confuses not sitting with physical activity".
What does matter, he argues, is a bit more nuanced – how you sit. Very long periods of inactivity are not good for you, in part because they seem to be linked with harmful low-grade inflammation. So "sit actively" – which, simply put, means fidget and get up regularly.
You may wonder why anybody ever sets foot in a gym. Being very strong is overrated and abnormal, he adds. Measurements of the grip strength of the Hadza tribe of hunter-gatherers – a community in Tanzania that are often studied as the best proxy that still exists to a truly ancient way of life – as well as estimates of their overall upper-body strength and muscle size, put them squarely within western norms, he writes.
Gym bunnies are unnatural beasts. Ancient humans could not access the calories required to preserve lots of muscle bulk. And being inordinately strong means that you sacrifice power (strength is how much force you can produce; power is how rapidly you produce it). For a foraging species, power – which makes you nimble and quick – is more useful.
We are also, he warns, in danger of being hoodwinked over how to lose weight, in as much as exercise might not always help. One study cited by Lieberman found that women who were asked to add 140 minutes of walking into their weekly routine lost only 5lb (2.2kg) after six months. Perplexingly, those assigned 210 minutes lost less – only 3lb (1.3kg).
One issue is that exercise triggers so-called compensatory mechanisms. Hunger is an example: working out will increase your appetite. Another hitch, as far as walking is concerned, is that we're very efficient at it.
Thirty minutes a day of brisk walking translates to roughly 100 calories, enough for an average person to shed 5lb (2.2kg) in six months – a drop in the ocean if you're morbidly obese. This doesn't mean that walking can't help you shed weight. "But to do so, one needs to walk considerably more than half an hour per day for many months," Lieberman writes.
At this stage, you might think that he is priming us to submit to our deep evolutionary urge to lounge – except, of course, he's not, because his research has also shown that as a species we were born to move.
Running runs in the family. In 1969, when he was five, his mother took up jogging. She was in her thirties, unfit and struggling with a stressful new job. It helped. "She gradually became addicted," he says. She got his father hooked too. "For more than four decades she jogged about five miles (8km) nearly every day, often with my dad, even in the winter."
Now in her eighties, his mother still goes to a gym almost every day. In turn, Lieberman took up running "seriously" in the early Noughties, when he began to study its evolution. He'll admit that he became slightly fanatical. "My poor wife had to put up with quite a lot," he says. "When I first ran marathons I had no idea what I was doing and I drove her crazy – I would get like Howard Hughes beforehand. I was afraid that I would get a cold from somebody and not be able to run."
While he was building up his early road miles, he was also tracing our evolutionary history, scouring the fossil record for evidence. What he saw was that roughly two million years ago, our ancestors' brains dramatically increased in size. Only meat would have provided the concentration of energy required to fuel a large, calorie-hungry brain. They were eating other animals.
But the first spears and arrows didn't appear until more than one million years later, and it is difficult to imagine our Stone Age forebears ambushing large prey without weapons: it's too risky. Instead, Lieberman believes that early humans developed two strategies: "power scavenging" and "persistence hunting". The first involved beating other scavengers to carcasses abandoned by large predators. The second involved pursuing large mammals for hours until they collapsed, exhausted. Both depended on humans being extraordinarily efficient at covering large distances.
He suspects that these ancient hunting strategies explain the highs reported by people who run – and dance – hard. "Long periods of vigorous exercise stimulate mood-enhancing chemicals in the brain including opioids, endorphins and, best of all, endocannabinoids," he writes.
Exercise is absolutely a good thing, he says – but we don't need too much. I mention that his description of "persistence hunting" makes our ancestors sound like elite athletes.
Stay mobile, but don't go crazy. Do plenty of cardio. Don't beat yourself up too badly when you slump into lazy habits.
But by today's standards they weren't, he replies. They probably walked about half the time and when they ran they were averaging 10-minute miles. "It's nothing like running a marathon at warp speed," he says. Today's leading marathon runner can knock off 26 miles at 4 minutes 40 seconds each.
The "commercialisation, commodification and medicalisation" of exercise have caused people to become misinformed, he says. "It creates certain kinds of perversities – the idea that you should run an ultra-marathon? It's bizarre. It's not necessarily good for you."
Just 150 minutes a week of physical activity is linked with a longer life. "And then the curve kind of levels off, right? More is better but doesn't give you as big a response – the curve flattens out."
So stay mobile, but don't go crazy. Do plenty of cardio and some weight training. A bit of high-intensity interval training (HIIT) is probably a good idea. But don't beat yourself up too badly when you slump into lazy habits. It happens to the most virtuous of us. In the book he describes how he once conducted an unscientific experiment at a meeting of the American College of Sports Medicine, a conference filled with professionals dedicated to the idea "Exercise Is Medicine".
He counted how many took the escalator versus the stairs. Of the 151 people, only 11 took the stairs, about 7 per cent. Worldwide, the average is just 5 per cent. "Apparently, people who study and promote exercise are no different from the rest of us."
Everything you thought you knew about exercise . . . Forget it
By Daniel Lieberman
Being lazy takes energy
If you are an adult male who weighs 82kg and you do nothing but sit in that chair for the next 24 hours, your body will expend about 1,700 calories. Seventeen hundred calories are a lot.
As I sit here writing these words, my heart is contracting 60 times a minute to pump blood to every corner of my body, my intestines are digesting my last meal, my liver and kidneys are regulating and filtering my blood, my fingernails are growing, my brain is processing these words, and countless other cells in every tissue of my body are busily replenishing themselves, repairing damage, fending off infection.
Our bodies are constantly making trade- offs that have been selected over millions of generations. One of the most fundamental is whether to spend precious calories being physically inactive or active. A calorie can be spent only once and you can spend a given calorie in just five ways: growing your body, maintaining your body (resting metabolism), storing energy (as fat), being active or reproducing.
If you climb a mountain today, you will have less energy to spend on maintenance, storing fat and (perhaps) reproducing. If you go on a diet, you will have less energy to be active or reproduce. And so on. Natural selection doesn't care if we are happy, nice or wealthy; it just favours heritable traits to enable us to have children.
Stated simply, we evolved to be as inactive as possible. No sensible adult hunter-gatherer wastes 500 calories running five miles just for kicks.
It's natural to sit
A growing chorus of experts who nag us to exercise condemn sitting as a modern scourge. Standing desks are all the rage, and people now wear sensors to keep track of and limit their sitting time. We have become exercised about sitting.
Although more people today are couch potatoes compared with their ancestors, we can take solace by comparing ourselves with apes. Over a 12-hour day, chimps are physically inactive for almost ten and a half hours. Even sedentary American couch potatoes are wildly more active than wild chimpanzees. If being idle is a normal, adaptive part of the human and ape conditions, then why and how can many daily hours of sitting really be so unhealthy?
Surprisingly, marathon runners who train regularly sit just as much as less athletic individuals. In fact, because these avid runners are often exhausted, they might sit more. If sustained periods of not moving cause harm, why are we simultaneously warned not to sit too much but also advised to spend more time – nearly one third of our lives – barely moving in a semi-comatose state of sleep?
Usain Bolt is slow
As fast as Bolt and other elite sprinters can go, they are unimpressive compared with ordinary four-legged animals. Bolt can outsprint skunks, rhinos, hippos and most tiny rodents. That's about it. Usain Bolt's world record of 23.3mph (37.4km/h) would have no chance against the vast majority of quadrupeds like zebras, giraffes, wildebeests, white-tailed deer or even wild goats. As for carnivores, even slower predators such as grizzly bears and hyenas could eat Bolt's lunch – not to mention Bolt – on the track.
Although Bolt leaves me in the dust when sprinting, we both have to stop after about 30 seconds and pant to recharge our molecular batteries and clear the acid from our muscles. The longer the chase, the better I might do relative to Bolt because I probably have more endurance. Fortunately for Bolt, that wouldn't happen, because if he turns around after 30 seconds to catch his breath, he would see the hyena eating me for breakfast. And therein lies an important reminder: even though the fastest humans have little chance of outrunning hyenas, to survive you sometimes need only be least slow.
A human can run faster than a horse
I found myself questioning my sanity in Prescott, Arizona, toeing the line on an October morning at 6am with 40 other runners and 53 horses and riders. A "Man Against Horse" race was born in the town's saloon in 1983. I bet my daughter I could beat one horse over the 40km course. Within minutes of the start, I was sure I was going to lose my bet. "See you later!" the riders shouted cheerfully as they easily passed us in the first mile of the race.
Resigned to my fate, I decided to just try to enjoy this stunningly beautiful place. But then, at about the 20th mile, I passed my first horse, whose rider had stopped to allow the animal to cool down. My heart leaped and I found new energy as I started to pass more horses. If I may brag: I beat 40 of the 53 horses despite an unremarkable time of 4 hours 20 minutes.
Even if you dislike running, your body is loaded with features from head to toe that help you run long distances efficiently and effectively. It is no fluke that ordinary runners can compete with horses in marathons.
We're not meant to be strong
If I were a hunter-gatherer, beyond lacking gym facilities, I'd want to be reasonably but not extremely strong. One potential drawback of bulking up too much is sacrificing power. Strength is how much force I can produce; power is how rapidly I produce it. There is some trade-off between the two: a strong woman may be able to lift a cow above her head, but not rapidly. In contrast, a powerful woman might not be able to lift as substantial a load, but she can hoist things more swiftly and repeatedly.
Even today, average sedentary human beings benefit more from power than strength. Many activities of daily living, such as lifting a bag of groceries and rising from a chair, require rapid bursts of force. Another drawback of being super-strong that mattered in the Stone Age is its caloric cost. Bodybuilders who can lift a cow must also eat as much as a cow (well, almost). Regardless, most of us are stronger than we think and never achieve our full potential because the nervous system sensibly inhibits us from going all out, thus tearing muscles, breaking bones and possibly killing ourselves.
We are more peaceable than we think
If you spend a week with a troop of chimpanzees, you'll observe numerous fights, some disturbingly brutal. Male chimpanzees frequently attack other males as well as females to gain dominance and control mating opportunities. Occasionally they kill. We humans are nicer. Visit a park in any town to observe a group of fellow humans and you'll see children playing, but it is highly improbable any adults are fighting. Instead, the adults are peacefully monitoring the children, hanging out or participating in sports like soccer and basketball. Even the most belligerent human groups ever studied engage in violence about 250 to 600 times less frequently than chimpanzees. Are adult humans so non-aggressive because we evolved to be slow and weak? According to consensus, the answer is yes. We traded brawn for brains. Instead of relying on speed, power and strength, humans evolved to cooperate, use tools and solve problems creatively.
It's normal to be averse to exercise
Like it or not, little voices in our brains help us avoid physical activity when it is neither necessary nor fun. Everyone, including the billion or so humans who regularly don't get enough exercise, knows that more exercise would be good for them. Annoying "exercists" who nag and brag about exercise rarely improve matters by reminding them to jog, take long walks, go to the gym and take the stairs.
Part of the problem is the distinction between "should" and "need". I know I should exercise to increase the probability I will be healthier, but there are numerous, legitimate reasons I don't need to exercise. In fact, it is patently obvious one can lead a reasonably healthy life without exercise. The 50 per cent of Americans who get little to no exercise aren't doomed to keeling over prematurely. To be sure, insufficient exercise increases their chances of getting heart disease, diabetes and other illnesses, but most of these diseases tend not to develop until middle age, and then they are often treatable to some degree. Even though more than 50 per cent of Americans don't exercise, the country's average life expectancy is 79 years.
Extracted from Exercised: The Science of Physical Activity, Rest and Health by Daniel Lieberman
Written by: Rhys Blakely
© The Times of London