Plain English with Derek Thompson - What Evolutionary Biology Can Teach Us About Diet, Exercise, and Staying Alive

Episode Date: April 2, 2024

What can the science of ancient humans and the lifestyle of hunter-gatherers teach us about how to be healthy today? Harvard evolutionary biologist Daniel Lieberman joins the show to talk about his provocative “mismatch theory,” why humans are dysevolved for the modern world, and why exercise is the ultimate miracle drug. Host: Derek Thompson Guest: Daniel Lieberman Producer: Devon Renaldo Links: Exercised, by Dan Lieberman https://www.amazon.com/dp/B082H3ZH44?ref=KC_GS_GB_US The Story of the Human Body, by Dan Lieberman https://www.amazon.com/Story-Human-Body-Evolution-Disease/dp/030774180X Learn more about your ad choices. Visit podcastchoices.com/adchoices

Nathan Hubbard, spring has sprung, the birds are chirping, and the pop girls are pop-girling. Oh, and you know what that means, Nora Prenziotti. Every single album is back. This spring is packed with new releases from some of the biggest pop stars in the world, including our girl Taylor Swift, and we'll be covering it all. We'll of course break down every angle on the tortured poets department, and we'll also cover new music from Beyonce, Duolipa, Maggie Rogers, Casey Musgraves, and Ariana Grande. It's Pop Girl Spring on every single album.

New episodes starting March 28th. On Spotify or wherever you get your podcasts. I want you to imagine a hypothetical. Tomorrow morning, the FDA announces that it's approved a new drug that glided through phase three clinical trials. Across thousands of subjects, the new medication showed the following benefits. It increased insulin sensitivity, stimulated mitochondrial. production. Improved cognitive functioning, maintained bone density, increase the elasticity of blood vessels, improved cardiovascular health, reduced levels of pro-inflammatory cytokines,

secreted proteins that accelerated calorie burn, reduced weight, added muscles, and effectively combated anxiety and depression. As for the side effects, the most common included a minor risk of muscle or tendon injury, with practically zero risk of death. What would we do if a drug like this came on the market? We would call it a miracle drug. We would say Medicare needs to pay for this for all seniors, no price is too high. And now returning to reality, I'm happy to tell you that this medical intervention already exists. It's just not a drug. You can't find it in any pharmacy, even though its availability to the American public is nearly universal. Because what I've just described to you is the commonly

understood side effect profile of exercise. If you think about it from a 30,000, 100,000 foot perspective, an alien's eye view of humanity, working out is incredibly strange. We leave our house, our work, our families, our friends. We go to a place filled with strangers, none or few of whom we will ever talk to, and in collective solitude, we schedule 30, 16, 90 minutes of time-bounded pain. It's a kind of madness when you think about it. And if you take the historical view, exercise is entirely unnatural to the human species. A caveman would never do CrossFit. Our distant ancestors whose biology and psychology, we largely share, did not exercise in any meaningful sense of the term.

They hunted, they gathered, they played, they walked and walked and walked. They did this to live, to survive. exercise is a modern invention created by necessity to account for the fact that we live in a world where we no longer have to be active. We must choose to be active. And so to simulate the ancient cellular and hormonal processes that our ancestors, ones called life, we go to the gym. As the Harvard evolutionary biologist Dan Lieberman writes in his book, Exercised, this is the paradox of exercise. something we never evolved to do is essential to our health. If you take this idea one level deeper,

the fact that modern humans have to do something we aren't evolved for is extremely unusual. It's a part of what Lieberman has called the mismatch hypothesis. The modern world is a sparklingly novel environment, and in many ways we are not fit for it. We are mismatched. We are dis-evolved for our modern world. To take one quick but illustrative example, you and I are built for an environment to crave

sugar and efficiently store energy as fat for a world where sugar and fat are scarce. And until very recently, they were. Before World War I, the average American ate half an ounce of fructose per day. Today, he or she consumes more than two ounces, a quadrupling of daily sugar intake in just one century. Our food systems are progressing at the warp speed of technology while our bodies evolve at the languid speed of evolution. And the price of this mismatch is all around us, insurging obesity and widespread cardiovascular disease and more cavities in our teeth and more cancer in our bodies. The point of seeing modern problems like obesity and the lack of exercise

through the lens of disevolution is not to make us feel bad about it. Quite the opposite, it's to help us understand just how blameless many of us are, how difficult some modern problems are to solve because they implicate the deepest history of our species. Our bodies are ancient pieces of machinery

built for a world with ample activity and scarce calories, but thrown into a world with ample calories and scarce activity, where, again, we have to choose, to be active, often by driving away from our homes, away from our offices to park in a lot and walk into a big room of strangers where we can torture our muscles in order to live. Today's guest is Dan Lieberman. He is the author of several books, including exercised, why something we never evolved to do is healthy and rewarding, and his previous work,

the story of the human body, evolution, health, and disease. We talk about his field of evolutionary biology, the concept of mismatch or disevolution, the myths of diet and exercise from sitting to sleeping and walking, and the weird wonder that is working out. I'm Derek Thompson. This is Plaintingeridge. Dan Lieberman, welcome to the show. Thank you. I'm delighted to be here. You are a professor of human evolutionary biology at Harvard University. What is human evolutionary biology? I and others in my department study how and why humans evolved to be the way we are. And we're also generally interested in the question of how that evolutionary story is relevant to the challenges that human beings face today. For someone in 2024, trying to ascertain answers to extremely modern questions like, should I eat the flame and hot Cheetos in front of me? What time should I go to bed tonight? What use is this domain with your long telescope lens? Why should we care about human evolutionary? biology to solve extremely 2024 problems? I think a simple way to answer that is that we weren't designed, we weren't engineered,

we evolved. And if you want to understand how and why we are the way we are, you have to know something about that evolutionary history. And it's not like a blueprint. I think one of the frustrating ways in which I think some people use evolutionary data and theory to think about how to live their lives is to think, well, you know, if hunter-gatherers do it, I should do it too, that's a very facile answer. But there is much to learn about how we use our bodies and how our minds work and how we behave from studying that evolutionary history. And that can help give us evaluate the costs and benefits of different ways to live one's life. I'm very glad that you called the paleo fetish facile because it drives me completely crazy. I am both very interested in your

work and what our evolution teaches us about the bodies that we arrived into this world with. But at the same time, when people hold up the sort of paleo experience or the crow magnet experience, the homo erectus, whatever, experience as being this North Star that we have to aim for, I always think, let's remember the moral code of those ancient civilizations. They were very different from us in many, many ways. We don't have to go back 20,000 years just to find health and happiness and flourishing in the 2020s. No, but if I can just interrupt you, We did evolve. Agriculture was invented only 600 generations ago. That's the number of generations of mice that have probably lived in my basement since this house was built. It's been a blink of an eye

that we've been living, eating farm food. In fact, in the Industrial Revolution was just a few generations ago. In fact, it's still ongoing in some parts of the world. We can learn a lot about what kind of bodies we have and what kind of minds we have from studying evolutionary history. But it's important to remember that probably the most important flaw with the kind of paleo thinking, the paleo fantasy that's sometimes called, is that we didn't evolve to be happy, to be healthy, to be nice. We only evolved to have as many babies as possible who could survive and reproduce. So we evolved to be healthy only the extent that health improves our reproductive success. So just because our ancestors did something doesn't mean that's optimal for us. In fact,

I hate the word optimal. It just simply means our ancestors did it. And that there's some information that we can learn from that. But of course, there are lots of things in the modern world that our ancestors didn't have, which I'm sure they would have loved to have, like, I don't know, sterile surgery, refrigerators, freezers, et cetera. But there are also things today that cause all kinds of troubles. And we call those mismatch diseases. And an evolutionary history helps us evaluate them. When we're studying our ancestors from seven generations ago, how do we know what we know? Well, we have to piece it together from various forms of evidence. I mean, we do have ethnographic evidence from hunter-gatherer populations that live around the world. There are still a few.

They're not many. And they're not entirely hunter-gatherers. but we can still learn a lot from them. We also have a really amazing archaeological record, which is filled with clues and information about how our ancestors used to live. We know what they ate to large extent. So we can put together a reasonably comprehensive picture about many aspects of our ancestors' lives. I was really joined to your work initially

because it provides an incredibly useful framework for thinking about what's become a major theme of my writing for The Atlantic and also of this podcast, which is something like the costs of modernity, or maybe the ironic downsides of progress. We do episodes about why young people are so sad, why Americans are so anxious, why aloneness has increased in America,

and why this is all happening at a time when, by many accounts, you might expect that the opposite would be true. We have more ways to be entertained, more ways to connect, more ways to be with other people. And into this confusion or into this conundrum, you've presented two books, the story of the human body and exercised,

that together hold up this really big idea, this very important or stable frame that I think brings a lot to the picture, which is something you call the mismatch hypothesis. You've already alluded to it in the last few minutes. I want to talk about this idea before we dive into the more somewhat self-healthy parts of the conversation,

which is the lessons of anthropology for diet and exercise and wellness. But let's start by getting this framework set. Could you please help us define the mismatch hypothesis? Sure. All organisms are a doubt. to a particular environment. Think about a zebra out there on the savanna eating grass, right? It's adapted to that particular environment. And evolution often occurs when the environment changes around animals. If you take a zebra and you put it in the Arctic, that zebra is going to struggle,

be mismatched to that environment. We've also changed our environments recently because of all there's all kinds of reasons for environmental change, but one of the biggest causes of environmental change is culture. We've evolved all kinds of new foods to eat. We've created new technologies, like shoes and chairs and elevators and shopping carts and television and iPhones, and the list goes on. Sometimes those things bring benefits, or in many ways they bring benefits, but in some ways, they call what we call mismatches. So mismatches are when you're inadequately or imperfectly adapted to a novel environmental condition. That's essence of a mismatch.

That zebra in the Arctic is clearly mismatched to its novel environmental condition. In some ways, we are mismatched to, say, eating too much sugar. I don't think that's a very controversial statement, or mismatched to, I don't know, McDonald's or, I don't know, lawyers. There's many kind of mismatches out there, and they're complex because most of them are environmental changes that bring some benefits, but they also at the same time bring some costs. The costs, in terms of health, we call them mismatch conditions. I'll give you a trivial one. We evolved to eat all kinds of food, but we never evolved to eat a lot of food with a lot of starch and sugar.

When we do that, the bacteria on our teeth go crazy. And if they get caught by our plaque, as they digest those sugars, they produce a lot of acid, which cause cavities. And so we get cavities. We're basically mismatched eating a high-sugar, high-starch diet. So we have to go to the dentist to have our cavities filled, and we have to brush our teeth and all that kind of stuff. Other mismatches, of course, are much more serious, right? We're mismatched to the same high-sugar diet. It can cause diabetes, type 2 diabetes, for example, or a wide range.

of dietary issues can cause obesity, which can cause some health concerns. So there's lots and lots of mismatches that occur basically again from our bodies being imperfectly or inadequately adapted to novel conditions. It's funny because a rant that I've gone on a thousand times with my wife is that I can't believe that human teeth in the 21st century are so pathetically bad. It's just astonishing how bad our teeth are at eating food and not falling and rotting out of our skulls. You can brush them twice a day with a special paste developed for our enamel. can floss, and they still develop cavities and rot out of your head. And then I read this sentence in your book. You write that 20 to 30,000 years ago, the typical fruit had approximately

the sweetness of a modern carrot. The idea that ancient mangoes and strawberries might have tasted like carrots and Brussels sprouts made me think two things. First, when people think they're eating a paleo diet in 2024 by eating only blueberries and bananas, they're not eating anything close to a paleo diet. You might as well not even try. They're eating a very modern and very sweet version of the fruits that have been cultivated over the centuries to be sweeter. But second, I think it cracked open a little bit of this mystery of our pathetic teeth. Our teeth are disavolved for the fruit aisle of our grocery store. Do the hunter gatherers that you study, do they consume sweets as well? Hunter Gathers love honey. In fact, I've gone out hunting with Huzza Hunter Gathers in Tanzania,

and when they fail to kill an animal to catch them game, they go wild just collecting honey. I mean, I once went out with some guys, two guys, and after a few hours of frustration in terms of their hunting, they went to five different beehives, not one, not two, not three, five different beehives, smoked the bees out and ate more honey than I knew a human being could possibly eat. And I'm sure that wasn't good for their teeth. Well, you're describing in a way the first chapter of disevolution, which is that we have always craved honey. We've always craved sugar. It's only in the last few decades, few centuries, that we've had access to not only more sugar than we could possibly eat, but actually in many ways, the sugary version of many foods is cheaper than the less sugary version of many foods. Like, I love yogurt, for example. And Greek fatty yogurt with less sugar is often more expensive than the most sugary yogurt.

That's right. Yeah, we pay extra money for them not to add the sugar to the foods that we buy. It's pretty incredible. But remember, those hunter-gatherers when they got that honey, which was, you know, I was just astonished about how much honey they were eating. Each time they got honey, they got stung by bees every single time. They had to generate smoke. They had to climb a tree.

It was serious work to get that honey. It was not trivial. Whereas we were just surrounded by sugar and it's now made from corn. It's super cheap. And so, of course, all that abundance of sugar were seriously mismatched to it. But we are adapted to love sweet things. There's no question about that. The way that I think about the mismatch hypothesis is that there are some examples of mismatch

that are examples of too muchness, and there are other examples of mismatch where in modern environments we're getting too little of something that we need. So I want to just hold on this sort of too muchness of food and calories. To what extent do you think this mismatch hypothesis is a fundamental explainer for modern obesity and the prevalence of cardiovascular and coronary disease? It explains almost all of it. Sure. There was probably disease in the past. There's no question about that. But to my knowledge, nobody has ever yet documented an obese hunter-gather. There might have been. There are these figurines that are sometimes called Venus figurines. I'm not real fan of that term. But anyway, that look like highly sexualized, very pregnant, but often

obese figurines, they were produced in the Ice Age 20,000 years ago or so in Europe. And people wonder if those are actually images of individuals who had obesity or if they're just kind of fantasies. Nobody really knows. But among the ethnographic record of hunter-gatherers, occasionally we can find a hunter-gatherer who would be by medically considered overweight. But obesity is basically non-existent. And that's because people had to work hard and they didn't have access to the kinds of foods that we have today. And the result was people stayed in more or less an energy balance.

So obesity is, I think, a classic example of a sort of a mismatch disease. And it didn't really begin to occur in human populations until. origins of agriculture. And of course, even then it was pretty rare. Only really wealthy people had the opportunity to put on that much weight. And of course, now with the Industrial Revolution, we've managed to produce all kinds of foods super cheap that we crave. And the result is, of course, and people don't have to be physically active. You can spend your whole day just sitting in a chair, essentially. And of course, the end result is weight gain. Another line from your book that I underlined and starred is that, quote, the incidences of coronary arthurosclerosis among the

scanned mummies of ancient Egypt were at least 50% lower than in Western populations. End quote. So right there, you were comparing mummies, a relatively privileged population within ancient Egypt, I had to think, who probably had access to a lot more sugar if they wanted it than the average Egyptian. You're comparing them to modern Americans or modern people in the West. They had 50% less coronary disease in modern populations. A really striking statistic.

So one evolutionary mismatch that we've been discussing, you could say, it's the mismatch problem of too much. There's too much caloric abundance. Another way to think about mismatch is to look at the categories where the modern world offers too little of something. And I think this is a good opportunity for us to talk about some of your work

on physical activity, exercise, and the difference between modern physical activity and ancient human physical activity. So let's start with a really clear picture in our head of the hunter-gatherer exercise regime. I feel like most depictions of the so-called caveman era of humanity, typically portray the hunter-gatherer as a sort of ripped ultra-marathoner type. How does that depiction stand up against what we know about hunter-gatherers?

For sure. We have all kinds of stereotypes about cavemen and whatever, but hunter-gatherers are pretty physically active, and they're reasonably strong, but they tend to be kind of small, and they do mostly endurance physical activity. So typical hunter-gathers walk five to ten miles a day. They often carry stuff. They often tropical environments. They spend a lot of time digging. things like that. And colleagues of mine, Dave Reiklin and Herman Ponser and Brian Wood, have measured, for example, put on sensors on Hudson-Hunter-Gathers. They're engaged in moderate to vigorous physical activity. That's when you get up to like 50% of your heart rate or more, like a brisk walker or more, about two and a quarter hours a day. That's what they do. Otherwise, they sit around. So they're reasonably fit. They're pretty active. They're about 10 times more active than your typical American. But they're not jacked. They're not like super strong. They don't run marathon. They don't swim the English Channel kind of stuff. They're just trying to get by. And, of course, for them, getting by requires every day being very physically active.

But you think about it this way. If I were to go to the gym and really bulk up and I can guarantee you I'm not one of those people. I try to do some weights occasionally, but I'm not super strong. If I added all that extra muscle, I mean, muscles are expensive. I would have to eat a ton of extra to pay for that. So we're adapted to be strong enough, but all that extra strength. would be really maladaptive in an environment where you don't have access to a huge amount of food. It would actually be a problem.

It is interesting that your book, Exercise has a subtitle why something we never evolved to do is healthy and rewarding. And it is interesting to think that as I was reading this book and going to the gym as I try to do, you know, four-ish five times a week, it was interesting to think that what I was engaging in had to be invented when we invented our way out of needing to exercise, essentially. And the exercise itself is a kind of play act of that which used to be called life. Well, it's important to distinguish between physical activity, which is just moving, just doing stuff, and exercise, which I define as voluntary, discretional, physical activity for the sake of health and fitness. And until recently, nobody exercised, right?

They were just physically active. But if I went for a five-mile run in the morning for no reason other than to stay fit, no hunter-gather would ever do that. That's a completely crazy thing to do. Is that right that no running for leisure? They must play games that might have some aspects of exercise built into them. I just want to understand that. Let's play.

So, again, we evolved to be physically active for two reasons and two reasons only, when it's necessary or when it's rewarding. So play is rewarding. It's also, and to some extent, necessary, too. I mean, it's important for learning skills and developing capacities and learning not to punch the other team, you know, when they score a goal and all that kind of stuff. There's lots of things you learn through play in sports, but buying a piece of metal who's soul function is to be lifted.

That's a really bizarre, modern thing. I think the strangest thing of all is a treadmill. This horrible, nasty machine that makes you work really hard and stay in the same place. And if you don't like treadmills, one of the things I'd like to remind people is that treadmills were actually invented in the Victorian era as a form of torture for prisoners. They would put prisoners in Victorian debtors' prisons on treadmills, like the earliest treadmills, kind of to make sure that they weren't enjoying themselves in prison. It's interesting that you would compare using the treadmill to torture because I'm someone who gets way below average amounts of endorphins for my workouts.

So I feel like almost all of my trips to the gym are a kind of torture. I'm torturing my legs when I'm doing the squats and torturing my shoulders when I'm doing lifts. The whole thing is just one long, bizarre, horrible feeling. And it is kind of bizarre to do it from the start, you know, which is why I loved your angle from the book. It made me feel less guilty for feeling like a stranger in a strange land when I'm at the gym. I want to take some of the rest of our time to talk about the exercise myths that you've uncovered from your work. And I think we should begin with a very popular pillar of modern health, which is sleep. From an evolutionary biology standpoint, what is it that you think that we in the 2020s get wrong about sleep?

Well, sleep is, of course, something that everybody does. But we've been told the standard story is that technology has ruined sleep. We have iPhones and televisions and lights and all kinds of stuff that keep us from sleeping and that our ancestors had perfect nights of sleep getting eight hours a night. Well, I've been in camps with a hundred gathers and in subsistence places where there's no electricity, and I can tell you, people are up all night, and colleagues have put sensors on folks in these environments. We now have data from different populations, and it's just not true. The old eight-hour myth is just not true.

And for the most part, people get about six, six and a half hours a night. Napping is actually turns out to be pretty uncommon. And again, these are people who have no, nothing they can plug in whatsoever in their world. And furthermore, I think we have this what's often called the sleep industrial complex. There's money to be made by making people stressed out about sleep. Oh, my God, you're not getting your eight hours of sleep. And so we sell them stuff and make them feel anxious about their sleep. And of course, anxiety just causes cortisol to rise.

Cortisol doesn't cause you to be stressed. Cortisol goes up when you are stressed, but it's an arousal hormone. And, of course, then it makes you harder for you to sleep. So I think, you know, it's true that people who don't get enough sleep, that is a problem. People who sleep too much, that can also be a problem, although usually that's the symptom of a problem, not the cause of a problem. But if you look at the sort of, if you were to draw on the X axis of a graph, you know, how much sleep you get a night on the y-axis, you know, health outcomes.

For most populations, it's a U-shaped curve. The bottom of that curve, so the so-called optimum, is about seven hours. And so making people feel bad if they don't get eight hours of sleep is not only wrong. It actually can potentially cause harm. One of my favorite articles that I wrote several years ago was about various efforts to look at how hunter-gatherers and other ancient humans slept because I'm someone who wakes up in the middle of the night all the time. I have what's sometimes called bifasic sleep. And there's lots of evidence that seems to suggest that many people around the world did not have one long continuous sleep. They slept a little bit.

They woke up in the night. They had some play. Maybe they had some sex. Maybe they ate some bread. And then they went back to sleep. And that all of these different languages throughout Europe and Africa and Asia referred to these sort of two different phases of sleep. And just learning that, learning that my waking up in the middle of the night was not some kind of modern, disorder, but rather a kind of anthropological echo of my ancestors made me feel so much better

about my midnight wakeups that I started to sleep better. And I do think there's this really extraordinary and sometimes really tragic feedback loop between the pressure that we put on ourselves to sleep well and our ability to sleep well. Well, sleep is just one of many behaviors that we've medicalized and commercialized and industrialized and sometimes in ways that don't help us. There is a lot of debate, though, about that first sleep and second sleep. And some of that comes from historical information. The hardcore data from hunter-gatherers indicates that most of them actually do sleep through the night. But of course, it is also totally normal to wake up in the middle and I can go back to sleep again. All right. Well, now I feel absolutely terrible. And I'm just going to have to find

some other piece of them that suggests that by phasing sleep is the norm. I'm only joking. I remember reporting on that that the original reports you know, suggested by phasic sleep was the norm. And then there was more research that suggested that no, in fact, a lot of extant hunter-gather communities in Tanzania and South Africa still have this sort of one connected sleep. People do everything. People do everything. Right, exactly. I think the key is just not to stress out about sleep.

And furthermore, another aspect of the sleep industrial complex is like you have to have a dark room with not a single photon of light and a completely comfortable pillow and mattress and all that. And of course, that's not how anybody slept until recently. I mean, people slept on the ground and with all kinds of chaos around them. and hyenas in the distance and people doing all kinds of stuff, having sex and making noise and gossiping and fighting and who knows what. And I think the evidence for that is people get on an airplane and like, bam, they fall asleep. And like talk about a completely weird,

strange, you know, mismatched environment and people can yet sleep on airplanes. I mean, that proves that we actually, if we decide not to worry about it, we can sleep pretty much anywhere. So speaking of industrial complexes, there's the sleep industrial complex. There's also a sitting industrial complex. We're constantly told that sitting is the new smoking. To what extent has your research indicated that sitting is a danger if we compare ourselves to our ancestors? Well, it's just farcical. Again, this is another way to scare people and make money. A hundred gatherers sit as much as we do. Dave Reikland, my former postdoc, a professor at a University of Southern California, has a functioned wonderful paper in the proceedings of the National Academy of Science showing that the

the haza sit for 10 hours a day, which is pretty much average for an American. Now, the difference is that they sit in more interrupted blocks. So Americans will sit down and stare at the TV for hours and hours and hours. Whereas if you go to a camp of hunter-gatherers or farmers, for example, where I work in Kenya or whatever, people get up and down and up and down, so they're constantly getting up and down. The other big difference is that we sit in chairs with backs and all that. And that's a pretty static form of sitting. But if you squat on the ground, where I work, there are no chairs.

You either squat or you sit on the ground. and that requires you to use muscles even when you're sitting and they're kind of turning those muscles on. And just that little bit of muscle function, it's like turning your car on without even necessarily driving anywhere. You're kind of turning on all kinds of genes and proteins. And that seems to have benefits in terms of decreasing the amount of blood sugar, for example, you might have or the amount of circulating fats or who knows what, lowering levels of inflammation. But the point is that sitting more actively, even if you sit a lot, seems to be more healthy than sitting highly passively. And if you look at the epidemiological data in places like United States, people get into trouble are not people who sit a lot all the time. It's people who sit not just for their work, but also leisure sitting.

So it's leisure time sitting, which is actually most strongly associated with negative health outcomes. And how about walking? You know, there's a lot of debate around this concept of 10,000 steps a day. I think it was that number was created by a Japanese company that just invented some new machine. And so now I think the modern response to it is, oh, 10,000 steps isn't something you should listen to because it was created by a company, which always makes me think, well, more steps are probably good. So if we're anchoring to a higher number, then that's not an altogether bad thing, even if that number came from a company. So inject some sense into this debate about stepping. What is a useful way to think about walking? Go ahead.

Yeah, so walking is the most fundamental form of physical activity. We evolved to walk more than anything else. And as I said before, you know, typical hunter-gatherers walk 9 to 15 kilometers a day. That's like 5 to 10 miles a day. But if you medicalize walking and you turn it into kind of a prescription and you try to come up with an optimal number, it's just impossible because there's no one, everybody's different. It depends on what age you are and what your fitness levels are. Are you worried about Alzheimer's or you're worried about diabetes or you're about heart disease? there are different outcomes. So a colleague here at Harvard, Iman Lee, who's done a lot of really

brilliant work on step counts and outcomes, shows that, for example, if you're interested in certain kinds of diseases, you get more and more benefit for more steps a day. And for most people, the kind of curve flattens out at, say, 7,000 steps a day. But for, say, heart disease, which is like another outcome measure, the more the better. The curve never stops. The more you do, the better you get. So 7,000 steps is better than 5,000 steps, but 10,000 steps is better than 7,000 steps. So there's just no one prescription. And that's part of the problem with medicalizing exercise. It doesn't really work. It's not like a pill. There's no one ideal sort of amount to take, one proper dose. It varies based on all kinds of characteristics of you, the

exerciser, and also the outcome that you're most interested in. Do we have a good sense of how many steps the average American takes in the 2020s versus how many steps a hunter gatherers seem to take in a given day? I don't remember the number exactly, but I think the average American takes 4,774 steps. Isn't it amazing we know that? And the average hunter gather, of course, there's not that many studies, but it's somewhere between 15 and 20,000 steps a day. 15 and 20,000. Oh, wow. Okay. That's quite a lot of steps. So 4,774. Is that what you said? Yes, that's exactly right. Well, sorry, at least for palindromic, we're way below, I guess, what is optimal.

You know, small wins. You got to celebrate them when you can. Is that from before or after the pandemic? Because I feel like I read that the pandemic. That's from before, yeah. Oh, yikes. Okay. Because I think I read a study that suggested that walking declined,

obviously during the pandemic when people were often shut in their homes, but also there was a lingering effect on reduced mobility after the pandemic. So we might be below that 4,700. Yeah, I mean, the effects of the pandemic will be felt for decades. Another interesting thing about the pandemic is there was also a kind of, as with so many other things, a difference between people of privilege and people who have less privilege. So some people had gyms and neighborhoods where they could walk around and actually responded to the pandemic by increasing their exercise and physical activity.

But, of course, others who had less fortunate went the other direction. The last lesson that I took from your book that I think is really important, even though I'm 37, is the relationship between weight training and age. I feel like there is a sense that as people get older, they should do more cardiovascular exercise, but it's not necessarily the case that they should go to the gym to do resistance training or weightlifting more. But tell me how that compares with the lessons that you've taken from your research? Let me break that up into two things. So first of all, I think there's a sense that as we get older, it's like normal to be less active. And that is definitely not true. In fact, I think the chapter of that book I'm most proud of is the chapter about aging

and physical activity. As we get older, the benefits of physical activity actually become more important, not less important. And we evolved as a species, not only to become grandparents to live several decades after we stop reproducing, but in order to be physically active during those decades, we're to help feed our children and our grandchildren. And in turn, that physical activity is healthy, is that it turns on all kinds of repair and maintenance

and remodeling mechanisms that slow senescence, that slow the aging process and fight disease. So actually, that lifelong physical activity helped our ancestors have long health spans. Health span is how long you live in the absence of chronic disease. And before modern medicine, health span basically equaled lifespan. So if you want to stay healthy for a long time, you have to stay physically active because that physical activity actually helps increase your health span. I think we already kind of know that.

But as we age, the kind of physical activity, one of the problems is that as people age, especially in the West, they often don't engage in that much strength training. So they might walk a lot, but they might not do weights. That's basically the way to put it in colloquially. And the problem with that is that the absence of doing strength physical activity, your muscles become. weak because muscles are I use it or lose it sort of tissue. They're expensive, right? So if you're not using your muscle, they atrophy. And that can cause frailty. The technical term in medicine is sarco penia. Sarko is the Greek word for flesh and penia is lost. So flesh loss. It's hard to forget that one. So what happens is that you get older and you get weaker and more frail,

then normal physical activity becomes harder to do. And that turns on a kind of vicious circle. So as you age, making sure that one does strength training becomes increasingly important because it avoids that kind of frailty that can really be damaging. And if we look at hunter-gathering populations or farming populations, subsistence farmers, people say they're working hard. They're carrying stuff. I mean, the village is where I work, right? There's no plumbing. So if you want water, you have to go carry it. You have to go down to a stream or a well or a spring, fill a giant cherry can.

carry it back to your house or your village. That requires enormous amounts of strength. People carry their children. They carry food. There's no shopping carts. There's no suitcases on wheel. So people did a lot of basic activities that kept them strong and avoid that kind of frailty in old age. Yeah, I'm underlining that one in my own head because I do feel like that's something that is not typically and clearly communicated, that the need for strength training, in fact, goes up as we age rather than flat lines or goes down. And in many ways, I think that is the opposite of a lot of people's sort of quiet assumptions of what physical fitness looks like.

Most bodybuilders, for example, not that people look to bodybuilders necessarily to determine their definitions of physical health. They're young, right? There's not a lot of older people that you look to to say, oh, wow, look at that older, strong person. And obviously that's because it's harder to build and maintain muscle as you get older. But it's harder maybe to think other than Arnold Schwarzenegger of like an older, or these days, I guess, Jeff Bezos, an older model of someone who gets stronger as they get older. And as a result, we sort of internalized that.

Ruth Bader and Ginsburg was. Oh, interesting. Yeah. Yeah, Ruth Bader and Ginsburg was actually a little exercise book that her trainer and she published on her sort of strength training regime. There are some examples of that. And the good news is that you don't need to do a ton of strength training to say fit in reasonably strong as your age. Lots of repetitions of not so crazy weights. can do an enormous amount to kind of maintain muscle mass or even grow muscle mass.

And there are studies which show that 90-year-old people can actually bulk up. I mean, you know, they're not turning into Argynege Schwarzenegger, but your muscles never lose the ability to respond to stress. I don't know if this is like an existential question to ask or just sort of like a sort of meta-mechanistic question to ask about the effect of strength training in senescence. But as you said, there seems to be a use-it-or-lose-it law somewhat inscribed into our DNA. And I wonder, have you ever thought, why does the body, why would the human body need the signal from exercise in order to avoid senescence? Well, there's two reasons.

The first is that many tissues are expensive. And then recently, you know, expensive calorically, right? And recently, energy used to be very limited. People struggled to get enough energy to get through the day. There was no, you know, Whole Foods or Star Market or whatever kind of, you know, there was no shopping. Food was limited. And so when food is limited, you have to make trade-offs between energy you spend on growth and maintenance and reproduction and physical activity. And so if you can save energy on one thing, you can spend that energy on something else.

And that might be just basically surviving. And so tissues that are very expensive, you don't want to have any more than you need. So again, going back to muscle, muscle is a very expensive tissue. Maybe a third of your body is muscle. And muscle takes up a good 20, 30 years. percent of your total metabolism. So you don't want any more muscle than you need. And so when we're physically inactive, it regresses and when we exercise, it comes back. That's one reason. The other is that remember, nobody lived in an environment where they were physically inactive. That wasn't possible

until recently, right? People had to be physically active day and day out. Hunter gatherers don't have weekends. They don't have retirement every day. All of them have to go out and hunt and gather for food. Subsistence farmers are not much different. They don't sit around and wait for their coin to grow watching it. They have to hoe and plow and weed and thresh and do all kinds of physical activity. It's hard, hard work. In fact, it's harder than being a hunter-gather. So it really wasn't until the age of machines that people stopped having to be physically active.

And in turn, we never evolved to turn on these maintenance mechanisms that are activated by physical activity and the absence of physical activity. And that's because, think about it this way, if I go for a run this morning, I didn't go for a run this morning because I went for a really long run yesterday. But if I had gone for a run this morning, let's say a five-mile run, right? That five-mile run would have generated all kinds of damage and stress. All the mitochondria in my muscles, there's a little kind of organelles that provide energy, right? When you exercise, they produce all these what's called reactive oxygen species. These are molecules that are highly reactive that cause like the browning in your apple or your avocado. They rust, right? These molecules are damaging, but when we exercise, we produce tons of antioxidants.

When we exercise, we create all kinds of damage to DNA, for example, but we produce enzymes that repair our DNA. We tear our muscles. We put cracks in our bones. I mean, every single system of your body is stressed. But physical activity, because we evolved to be physically active, we evolved to turn on, for every single one of those forms of stress and damage, we evolved to turn on mechanisms that repair them. And furthermore, because you don't want to have a lingering damage, we evolved to kind of overshoot. So we produce more antioxidants, for example, than you need. We produce more enzymes to repair your DNA than you need. And since we never evolved not to be physically active, we never evolved to turn on those repair and maintenance mechanisms as much in the absence of physical activity.

So that's why that stress that's caused by exercise is so important for fighting senescence, because we never evolved to kind of take care of our bodies in the absence of that stress. It's a great answer that goes right back to this thesis of mismatch and disevolution, right? That we evolved to fights in essence through physical activity. But we have emerged or have fallen into this world, born into this world, where we have to many times choose to be active rather than need to be active in order to live. And that's a strange thing to do, right? To choose to go to a gym, pay money to run on some treadmill in a stinky place with fluorescent lights. It's pretty weird. Yeah.

Especially weird when you think about how. fundamental it is. You're going to this smelly, sweaty place in order to turn on the very mechanism by which you have been evolutionarily evolved to survive. It is odd. Actually, I want to close by going actually to the top of the funnel here. So I might have gotten this stat from your work that just 20% of Americans get the minimum level of exercise according to the World Health Organization and other international groups, which is about 140, 150 minutes a week. That means 80% of Americans do not get the minimum level of of exercise in order to be considered active. You have all of this research on how exercise and

physical activity leads to health. But if we go upstream of that causation, I wonder if you've given thought to what behaviors lead to exercise, right? We live in a world where we no longer have to be active. We live in a world where we have to choose to be active. Is there anything you know, either from the field of human evolutionary biology or some other field, where we can essentially pull a lever on this 80% of the population that is definitionally inactive and say this is either environmental stimulus or policy or change that can help people choose to be more active. Well, I think there's several levers, if you want to call them that. The first is to help people understand that their disinclination

to exercise is completely normal. I think people are made to feel bad, they're made to feel ashamed, they're made to feel blamed for completely natural normal instincts, right? The example I always trod out is that if you're in an airport or a mall or, you know, somewhere where there's an escalator next to a stairway, even though there were no escalators in the Stone Age, it's just an instinct to take the escalator to save energy. And we're made to feel like there's something wrong with us if we do that. And there's nothing wrong with you.

You're actually being a completely normal, sensible human. being to save energy. Because we now have to, as you say, we have to choose to be physically active rather than you have to override that fast brain and our slow brain has to override it and say, no, actually you're probably better off taking the stairway. But that's hard. So that's the first thing. I think the second thing is to recognize, again, that we have all to be physically active for two reasons and two reasons only when it's necessary, rewarding. And so we want to help each other, help ourselves or help our friends, help our communities, be more physically active, we have to find ways to make it either necessary and or rewarding. And necessary is, well,

that's what we do for kids in school. And I think we should do a lot more to help kids in school be more physically active. There are a lot of physical education programs that essentially fail by overemphasizing, for example, sports where not everybody gets to participate. They can create feelings of discontent and so on. And kids who could get picked last, we know there's data that shows that they're less likely to exercise when they're adults. We can also re-engineer buildings and our environments to make sure there's more opportunities to be physically active. You know, make stairs more easy and elevators, you know, we need elevators for people who have disability and so on, but make that the alternative, nudge them basically to take the stairs. And then finally,

and I think most importantly, I think we should stop prescribing and medicalizing exercise and said find ways just to make physical activity fun. And I think the best way to do that is to make it social. Who thinks of dancing as exercise, right? But dancing is a form of physical activity that is highly social that every culture engages in, often endurance dancing. And why don't we do that more, right? Why don't we have more opportunities for people to walk together or when they exercise to do that in groups? And then it seems to become exercise. It becomes a social event. It becomes fun. And there's a lot of ways in which we can do that. It's just that we devote very little effort and attention to do that.

And I think with those kind of changes, we can help people. Because most people who are inactive, they don't want to be inactive. They know full well that they should be more active. It's just that they either lack the resources or the environment or the social milieu that makes it either necessary or rewarding. I write a lot and try to do a lot of episodes on happiness, on anxiety, and on longevity. And it's such a boring answer and yet a true one that in many ways, I believe this is

clinically borne out. For many people, the best antidepressant is exercise. For many people, the best longevity pill is exercise. And it's interesting to think that if you come at this from the policy angle, I mean, how many billions of dollars and how many debates do we have at other pharmaceutical companies or within the U.S. government about how to build a better antidepressant or how to invest better in longevity medication, it seems maybe a little bit strange and probably, you know, big brothery to have something like an exercise policy for a country. But I feel like if you take the effects

of exercise seriously, it's almost strange to not have a policy. Like the stranger thing in a way is to look at a country where 80% of Americans get below the minimum level of exercise and say, this is something that government should not care about or respond to with any kind of policy. That seems like the stranger thing. And I don't want to be one of these kind of people who happens to. I do live in Washington, D.C., think that the solution to everything is just another piece of legislation or executive order. It is interesting.

I'm just noting it here. It is interesting that some of these issues that seem like the most important ideas in the country, whether it's the decline of socializing or the decline of exercise, we don't really think of them as policy. problems. We think of them as problems that policy can't make contact with. And that's just kind of strange. I don't know. That's my final thought. You can have the final thought of the episode. Well, we live in an environment where we believe very strongly in personal responsibility and people who overeat or don't exercise, we consider it their responsibility. And I think,

well, the evidence shows that's completely not true. But I think if there's one, you know, nobody likes to be told what to do. Nobody likes to be told to exercise. Prescribing exercise usually fails, right? If a doctor tells somebody to exercise, that doesn't really have much. effect. But if we help people make it both necessary and fine, but also help them understand or appreciate more the immediate benefits, right, in terms of mood, right, and depression, anxiety, those benefits are profound and rapid and they can be powerful incentives. And the last word I will say is this. If you're struggling to be physically active, you don't need to run a marathon, right? Anything is better than nothing. And that anything can lead to yet more and yet more

and becomes less unpleasant and more pleasurable. But the most important thing is if you're struggling to be physically active, find friends, find colleagues, find others who want to do it with you, and then it ceases to become a drudgery. It becomes, you know, a social event. And then it transforms the experience into something that we've been doing for millions and millions of years when our ancestors went out every day walking and they were gossiping and they were chatting and they were doing all kinds of stuff.

I don't think it was. It's not exercise for them. It's just how they live. Dan Lieberman, thank you very much. My pleasure. Thank you. This episode was produced by Devin Ronaldo. We're back to our two times per week schedule next week with episodes on Tuesdays and Fridays. We'll see you then.

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