Harvard Professor: They’re Lying To You About Running, Breathing & Sitting! - Daniel Lieberman

1. 0:00 – 2:15

   Intro

   1. DLDaniel Lieberman0:00

      Cancer, violence, aggression, obesity, stress. If you want to fix all your complex problems, well, this is controversial, but the vast majority of the evidence suggests that-

   2. SBSteven Bartlett0:09

      Daniel Lieberman, a Harvard professor who uses the information of our evolutionary past- ... to understand the health crisis we are in today, and educate people on how to live a long, healthy life.

   3. DLDaniel Lieberman0:18

      The vast majority of us in the Western world will die from a mismatch disease. Chronic stress, that's what we call a mismatch. Obesity, heart disease, many cancers are mismatches, and it's because we now live in a world where we're able to have incredible levels of comfort with all this choice. For example, the number one medical complaint is back pain, because I'm sitting in this comfortable chair. I don't have to use any of the back muscles. So we develop weak backs that don't have any endurance. We know that people who sit a lot at work but then also sit a lot in their leisure time run way more risk of disease. And if you aren't physically active, you don't grow as much skeleton, and then when you hit 25 to 30, for the rest of your life, you're gonna start losing bone.

   4. SBSteven Bartlett0:56

      Oh, sugar.

   5. DLDaniel Lieberman0:57

      Even in this highly sanitized world, we're much more likely to develop allergies and various kinds of autoimmune diseases, because our immune systems are so unchallenged, they end up accidentally attacking us. Also, famous studies show that the richer the country, the higher the rate of cancer. Bangladeshi women who move to England, their cancer rates go way up because of diet and physical activity and stress, things that have changed in our modern world for which we are very poorly adapted.

   6. SBSteven Bartlett1:20

      There's a lot to take in. Is there an actionable conclusion that I can do today that is going to reduce my chances of getting one of these mismatch diseases?

   7. DLDaniel Lieberman1:26

      Yes, I think there's two. The first is-

   8. SBSteven Bartlett1:31

      Quick one. This is really, really fascinating to me. On the back end of our YouTube channel, it says that 69.9% of you that watch this channel frequently over the lifetime of this channel haven't yet hit the subscribe button. I just wanted to ask you a favor. It helps this channel so much if you choose to su- subscribe. Helps us scale the guests, helps us scale the production, and it makes the show bigger. So if I could ask you for one favor, if you've watched the show before and you've enjoyed it and you like this episode that you're currently watching, could you please hit the subscribe button? Thank you so much, and I will repay that gesture by making sure that everything we do here gets better and better and better and better. That is a promise I'm willing to make you. Do we have a deal?

2. 2:15 – 3:24

   What do you do, and why do you do it?

   1. SBSteven Bartlett2:15

      Daniel, what is your job title?

   2. DLDaniel Lieberman2:18

      I am a professor of human evolutionary biology at Harvard University.

   3. SBSteven Bartlett2:23

      And what does that mean?

   4. DLDaniel Lieberman2:24

      (laughs) It means I get to have a lot of fun. Um, I study, uh, well, my department studies how and why humans are the way we are, and we're also interested in how and why that's relevant to, to humans today. Uh, my particular specialty is I study the human body. I'm interested in how and why the human body is the way it is and how that's relevant to health and disease, and I am most interested, most of my work is on the evolution of human physical activity, but I'm also interested in diet and, and, and other ways in which we use our bodies.

   5. SBSteven Bartlett2:55

      Why does it matter?

   6. DLDaniel Lieberman2:57

      Well, because we weren't designed, you know, we weren't engineered. We evolved, right? So if you want to understand why we are the way we are, you have to understand that evolutionary history. And, and if you wanna solve problems, if you wanna deal with, you know, big issues that we face today, obesity, you know, heart disease, cancer, violence, aggression, all of these things have an evolutionary origin, and an evolutionary origin is, is crucial to, to helping us come up with solutions.

3. 3:24 – 5:26

   Are we actually a good species?

   1. DLDaniel Lieberman3:25

   2. SBSteven Bartlett3:25

      Does what we eat play a role in the sort of starting point of our stories and how we began to eat? I'm thinking about farming, hunter-gathering, um, and all those things, 'cause when I look at human beings versus a lot of animals, and you talk about this in the book, we are remarkably fragile and, and inadequate in comparison. Like our eyesight isn't that great.

   3. DLDaniel Lieberman3:42

      (laughs)

   4. SBSteven Bartlett3:42

      We're like super weak. I think you say that like most monkeys are stronger than we are. Squirrels can run faster than us.

   5. DLDaniel Lieberman3:50

      (laughs) Well, I think we actually exaggerate our fragileness and weakness to some extent. So, so chimpanzees, our closest relatives, um, are about, probably about 30% stronger than we are. Um, you would not wanna arm wrestle a chimpanzee, right? Um, and most quadrupeds, um, can run way faster than we can, right? We are, we have this sort of story about human evolution, that it's been a sort of triumph of brains over brawn, right, that we have this, we have tools and language and, and that has enabled us to sort of conquer, you know, the world and become the dominant species, and there's some truth to that, of course. Uh, technology, uh, language, communication, cooperation, all are essential parts of the human success story. Um, but, you know, I think as athletes, we're pretty impressive. We can outrun most animals over long distances, so we're, we're really impressive in terms of endurance, both men and women. We can throw, we can kick, we can do all kinds of things that my dog can't do. As far as diet is concerned, you know, we're, we're the ultimate omnivores. We can eat anything. Um, I mean, most animals have a very kind of constrained diets. There are certain things they can eat, and most of the things out there they cannot eat. We've managed to figure out because of technology, cooking, food processing, but also because of the nature of our, of our digestive system, we can eat just about anything on the planet, right? People can be vegans, they can be, you know, they can eat all meat diets. They can... You know, it's, it's astonishing how much variety humans can get by with. Um, our d- you know, our livers can turn anything into anything. You can, you can, we can turn fat into carbohydrates, carbohydrates into fat. We have an incredibly astonishing range of foods that we

4. 5:26 – 7:47

   Do our ancestors hold the answer to all our health needs?

   1. DLDaniel Lieberman5:26

      can consume.

   2. SBSteven Bartlett5:27

      When we're thinking about our sort of evolutionary history and, and the hunter-gatherer tribes that still exist in the world, I think I've fallen into the trap of believing that all the answers we're looking for about how to be healthy humans-

   3. DLDaniel Lieberman5:38

      (laughs)

   4. SBSteven Bartlett5:38

      ... in the modern world can be found just by looking back at our hunter-gatherer ancestors. Is that true, that they hold the answers to how to live a happy, healthy life?

   5. DLDaniel Lieberman5:47

      (laughs) Well, it's... Like everything, it's complicated, right? I mean, to some extent, um, we call that, uh, paleo fantasy, this idea that if you just go back to being a hunter-gatherer that you'll have no problems, right, and that hunter-gatherers have no violence and they don't get sick and, you know, all is well. Well, i-It's not so simple, right? F- I'll give you one example. Murder. We have this idea that, you know, humans have become incredibly violent since the origins of farming, right? But if you actually look at the ethnographic record, hunter-gatherers are, are just as (laughs) violent as the rest of us. They're, they're human beings. Um, they, they, they, they kill for passion, they kill for greed, they kill for, uh, you know, for... You know, there's murder. There's warfare among hunter-gatherers, even, in some parts of the world. Yes, it's true that hunter-gatherers don't have a, uh, the same problems with obesity. They don't have metabolic syndrome. They don't have, um, they probably don't get heart disease, at least to the extent that we do. There are plenty of things that they do that are worth, um, emulating. But, but they're not role models in every respect, and you know, what natural selection cares about is how many offspring we have who survive, right? That's the only thing natural selection cares about, is the equation of life is food in, babies out, right? That's what, that's what we're here for, right? As far as natural selection is concerned.

   6. SBSteven Bartlett7:03

      Not happiness.

   7. DLDaniel Lieberman7:04

      We're not here to be happy. We're not here to be nice. We're not here to be fulfilled or anything like that, although it's good when that happens, right? We evolved to be hunter-gatherers. Our ancestors were hunter-gatherers for millions of years, but those, uh, but the, the adaptations they have are primarily and first and foremost about reproductive success. So we didn't evolve to eat foods to make us healthy. We evolved foods that would increase our reproductive success, and we evolved to be healthy only to the extent that health promotes reproductive success. So you, you can't just assume that because our ancestors did something, it must... It's, it's optimal for health. It's, you can... It's more reasonable to assume that that's optimal for reproductive success, and remember, it's in those environments and in those contexts

5. 7:47 – 10:48

   Have we evolved to eat meat?

   1. DLDaniel Lieberman7:47

      and things have changed.

   2. SBSteven Bartlett7:48

      Talking there about what they eat, one of the big debates of, I guess that's an ongoing debate, is whether we are evolved to eat meat or we're meant, you know, we're meant to be, interesting use of words, vegans or vegetarians. What's your perspective on that? Because I've, I've sat here with people, um, who are really, really passionate about the fact that we're not supposed to, evolutionarily, see how quickly I tried to say that word? Because I don't know how to say it, um, meant to eat meat.

   3. DLDaniel Lieberman8:15

      Well, that's just nonsense. (laughs) I mean, humans have been... Humans started eating meat about two and a half million years ago. There's no question. At least two and a half million years ago, maybe more, and there is no question it played an extremely important role in our evolutionary history. Even chimpanzees, our closest cousins, eat meat occasionally when they can. They don't get it very often. Uh, maybe about less than 5% of their diet is meat. You know, from an evolutionary perspective, we evolved to have meat as part of our diet. But, but of course you can be a human being and not eat meat and do just fine. In fact, there are some advantages, because remember, we didn't evolve to be healthy. So just because our ancestors ate meat or didn't eat meat doesn't mean that's optimal for health today, right? That's, that's very... Sort of impoverished way of thinking. It just, it's just illogical, right? Um, our ancestors didn't evolve to, to, to read. So should we not read? Reading is only a few thousand years old, right? So it, it doesn't... You know, that's just not the right way to think about, about how to use evolutionary theory and data. The fact of the matter is that we evolved to eat just about everything. We are the ultimate omnivores. It's astonishing the range of foods that we eat. Hunter-gatherers eat... You know, a typical hunter-gatherer in the... Like, for example, there's data from the Kalahari. I think they eat about, uh, like 800 different kinds of plants.

   4. SBSteven Bartlett9:32

      Hmm.

   5. DLDaniel Lieberman9:32

      Many different kinds of animals, right? And that's just the Kalahari. Humans moved over the last, you know, few hundred thousand years to pretty much every corner of the planet. And in every part of the world, they found foods to eat. Humans live in the Arctic where there's almost nothing but meat to eat in many seasons, and you know where you get plant food in the Arctic in the winter? By eating the contents of the intestines of, of the animals that they-

   6. SBSteven Bartlett9:58

      Oh, really?

   7. DLDaniel Lieberman9:58

      ... they hunt, right? Um, people evolved to live by, by oceans and, and, and fish and, and dive for shellfish and, you know, eat shellfish. I mean, it's... They, they live in, in rainforests and eat bugs and, you know, birds and monkeys. I mean, everywhere you go on the planet, people figured out to eat various kinds of foods. And one of the ways that we became so omnivorous is that in addition to having an incredibly flexible digestive system, we also have technology to, to process our food. So by cooking our food, by fermenting our food, by grinding, cooking, cutting it up, we've been able to essentially adapt ourselves to an astonishing range of environments, hence an astonishing range of foods. And so, so now tell me, like, what diet are we evolved to eat, right? It's an impossible question to answer.

6. 10:48 – 17:18

   How did we learn to hunt and gather?

   1. DLDaniel Lieberman10:48

   2. SBSteven Bartlett10:48

      Is there a point in our history where we learned how to hunt and gather, and was that the point where we started really eating more meats?

   3. DLDaniel Lieberman10:58

      Yes. So... Well, first of all, it probably wasn't like a, you know, a-

   4. SBSteven Bartlett11:02

      A day. (laughs)

   5. DLDaniel Lieberman11:03

      ... you know, (laughs) you know, a lightning bolt came down from the sky and all of a sudden, bam, you know, so we figured out how to hunt. After all, our ape cousins will hunt when they can. But as soon as we became bipeds, which is probably around seven million years ago-

   6. SBSteven Bartlett11:17

      That's right.

   7. DLDaniel Lieberman11:18

      ... walk on two feet, right? We became slow, right? You know, chimpanzees, when they run, can gallop essentially on four legs, right? And, and that, and they can be really fast. They can't run long distances, but boy, are they amazingly fast, and they can climb up trees like, like no human can. Around seven million years ago, when we split from the chimpanzee lineage, it looks like we became obligatory two-legged bipedal creatures. And it's when you have only two legs, you can only run half as fast as when you have four legs. It's like having a cylinder... Car with half the number of cylinders, right? You know, you can just produce less power, right? And so our early ancestors must have been slow. There's no way they could have run that fast, and certainly not fast enough to be great hunters. So I suspect that compared to chimpanzees, they were probably poor hunters because they couldn't run down creatures the way chimpanzees could, right?So probably for a few million years, meat was probably rare in the diet. But then we begin to see, starting around, you know, around three million years ago, maybe a little bit older, stone tools in the archaeological record. We find bones with some cut marks on them. And starting around, you know, 2.5, 2.6 million years ago, we have archaeological sites with, with bones of animals with cut marks on them, stone tools, and those animals were clearly butchered. And by two million years ago, we have clear evidence that humans were, were, were actually hunting. You know, we have, we have clear evidence that these animals weren't just scavenged, they were definitely hunted. So that means that sometime between three and two million years ago, hunting became part of our ancestors' repertoire. They're also making tools. They must have been cooperating. Uh, they probably had some form of communication or whatever. We don't know exactly what it's like. And they're probably e- e- eating a wide range of foods, including, including what we call extractive foraging. So they're, they're eating tubers, underground storage organs, right? So instead of just plucking berries off plants, you know, they're, they're actually finding high quality foods that you have to dig for, right, under the ground, right? It's like, just think about a potato. It stores its energy underground. So there's a, these are rich sources of food but you have to be able to dig for them and find them, right? So this combination of extractive foraging, so not just, not just plucking leaves or berries off plants, but finding high quality resources, hunting, cooperation, tool making and tool using all together, that's the hunter-gatherer way of life, right? And that emerged some time, again, between three and two million years ago, and that was transformative. That's the, that's really, I think, one of the most important shifts that occurred in human evolution, and that's also incidentally when we see this shift in our bodies, right? When we, when we're going from being more, essentially more ape-like, like Australopithecus which had short legs and long arms and they have small brains, and you know, they're, they're not apes but they're, but they're more ape-like, to basically bodies that are more or less like yours and mine. So we have a, uh, a fossil called, uh, the Turkana Boy. His real name is Naria kotome. He's from the west side of Lake Turkana in northern Kenya. He's a Homo erectus, uh, who was probably about eight years old when he died. And, you know, from the neck down he's basically like you and me. Um, his, his, his head is not quite like ours, but he's, he has a big brain, not as big as ours. He has a, doesn't have a snout like a, like a, like an Australopith. He's got a vertical face. Uh, he's got teeth that are basically like yours and mine. He's basically very, you know, on that path towards being a human. And so hunting and gathering and the genus Homo kind of come together, and that was, I think, one of the most important major shifts that occurred in our evolution. Maybe the most important, actually. More important than even the evolution of our own species.

   8. SBSteven Bartlett15:01

      And that allowed us to, to become good hunter-gatherers. So we have this nose that sticks out of our face whereas like, a lot of our cousins look more like Voldemort. Like, they kind of have the-

   9. DLDaniel Lieberman15:10

      (laughs)

   10. SBSteven Bartlett15:10

       ... invert. And that's an, a sign that, of when we became hunter-gatherers, right?

   11. DLDaniel Lieberman15:14

       Yeah. So that external nose, right? So a chimpanzee has a flat nose like a dog, right?

   12. SBSteven Bartlett15:18

       Mm-hmm.

   13. DLDaniel Lieberman15:19

       And that external nose that you and I have, which is of course fantastic for holding our glasses, right? Well, you don't have glasses. Not yet, at least. Um, uh, is, um, is, um, a, uh, we think it's a kind of a humidifier. So when air goes into our nose, it has to go through a little nostril, so it's a little, what's called a Venturi throat. So it, it goes through a very narrow, um, bore and then into a, a larger space. And it has to turn a right angle to get into the inside of our nose, and then it has to turn another angle to get down into our, that pipe, we call that the pharynx, that brings air to the, down to our lungs. And all those twists and turns and, and changes in diameter cause the air to be more turbulent. So the air, instead of flowing, uh, in a kind of a, you know, straight, right? Um, bec- it has these vort- vortices. It's g- it's got all kinds of currents. And when that happens, that means that the air has more contact with the, the, the m- the mucous membranes in our, in our nasal cavity, so it can pick up moisture on the way in.

   14. SBSteven Bartlett16:19

       Mm-hmm.

   15. DLDaniel Lieberman16:19

       Pick up heat on the way in so our lungs are, um, don't get dried out. And on the way out, it can recapture that moisture so that we don't, um, we don't lose that, uh, moisture when we're, um, when we're walking or, for that matter, running. So, um, if you, on a really cold day, you can do a simple experiment, right? When it's below freezing, if you breathe out, ha, right, you see all that steam coming out. Do the same thing, breathe out through your nose, you'll see a lot less steam. And that's evidence of this, this ability of our, of our, of our noses to trap air. Um, and that's because of this external nose. So, so that happens around two million years ago or so. Um, we can see that 'cause on the f- in the fossils, we can see the, the margin of the nose, and you can see that it's lipped out. It's, what we call everted, right? It sticks out and that's evidence that we had these cartilages that sticked out, stuck out and, and gave us our modern nose. So, so if yeah, if you went two million years ago and you met an, your, your ancient ancestors,

7. 17:18 – 19:43

   Have we evolved to breathe wrong?

   1. DLDaniel Lieberman17:18

      they would've had a nice schnozz.

   2. SBSteven Bartlett17:20

      Does, what does this say about how we breathe today? Because I've, there's been a huge conversation, I think, over the last couple of years about breathing and breath, breath exercises, and mouth breathing in particular. Um, I've had people on this show like James Nestor who talks about how there's a lot of disease happening because we've kind of, by habit, become mouth breathers when we run. (gasps) Um, but also so many people seem to be having a lot of problems with their sleep. My girlfriend, for example, she uses nasal strips when she sleeps to try and, like, open up her airways, and I th- actually think she's gonna have to have an operation. But we've even got people in our team that are, seems like everyone's nose is... What, what do they call it when it's bent, the, the middle?

   3. DLDaniel Lieberman17:59

      A deviated septum.

   4. SBSteven Bartlett18:00

      A deviated septum. Seems like everyone's struggling with this at the moment.

   5. DLDaniel Lieberman18:04

      Yeah. (laughs) I have to say, I'm a little skeptical of some of these arguments. The idea that you can fix all your health problems by just breathing through your nose, um-Look, breathing is obviously very important, but, um, but the idea that, for example, when you run, you should only breathe out through your nose, that's just, that's just silly. Um, uh, that's just not true. We evolved to breathe out of our mouth when we run, we're the only species that does that actually, because it's a- an efficient way to dump heat. When you're running, you're generating huge amounts of heat, you have to dump it or you'll get a overheat.

   6. SBSteven Bartlett18:34

      Hmm.

   7. DLDaniel Lieberman18:34

      Um, and you, you, you breathe out through your mouth for that reason, right? To, to kind of, um, to, to get the heat out of there, right? Uh, breathing through your nose would be maladaptive and no elite runner on the planet breathes out through their nose when they're, when they're running. Um, I'm not sure where that came from. And I'd just like to see more data to support some of these arguments about nasal breathing. I'd like to see data to support the, the effectiveness of those, of those nasal strips. Uh, sure, uh, uh, breathing is important, there are better and worse ways to breathe. You know, we're always looking for simple solutions, right, to complex problems. And the idea that somehow fixing your breathing is gonna prevent you from having a wide range of diseases is, um, not true. And people who have sleep apnea, which is a serious issue, um, uh, that's usually caused by... Well, it's caused by a variety of things. Of course, a deviated septum might be one of them. Uh, obesity can cause it, there's a number of other problems. And of course, once that occurs, um, you know, again, you wanna treat the cause not the symptom, right? So, the best way to treat the cause of the apnea is not to put a piece of tape on your nose, it's to, it's to, it's to find the underlying cause about why that's happening in the first place and solve that, and deal

8. 19:43 – 24:38

   Why do we sweat?

   1. DLDaniel Lieberman19:43

      with that.

   2. SBSteven Bartlett19:43

      And is sweating sort of correlated to that turn in the f- the fork in the road in our sort of hunter-gatherer history? Because monkeys and even my dog, Pablo, he, he doesn't seem to sweat from anywhere other than his mouth, I guess. It seems like he's, his panting is his way of...

   3. DLDaniel Lieberman19:57

      Exactly.

   4. SBSteven Bartlett19:58

      Yeah.

   5. DLDaniel Lieberman19:58

      Exactly. So, the way in which most animals cool down is by panting, right? They, they breathe, uh, through their mouth or their nose, right? And there's, there's, uh, air passes over these mucus membranes on the, uh, on the, in the nose and the mouth, and, uh, and, and, um, and what happens is that the air, uh, by passing that air over the tongue or whatever, causes, uh, you get evapotranspiration. So evaporation. So the air, the, the, the, the moisture in that goes from a liquid to a gas phase, right? And that, of course, costs energy. So because energy is... Because of conservation of energy, that means that for every, I think milliliter of oxy- of, of water that goes, that goes from wa- water to gas, I think it's 561 calories, calories with a small C. And that, so that causes the tongue or the surface of the nose to cool, and then there's blood right behind that. Blood in, blood in the tongue. Think if you cut your tongue, it's really bloody, right? If you cut your nose, right? And it's a lot of blood, there's a huge amount of vasculature in there and all these arteries and veins, right? So that you cool then the blood that's just below the surface of the tongue and in the nose, and then that cools down your body, right?

   6. SBSteven Bartlett21:08

      Oh.

   7. DLDaniel Lieberman21:09

      So that's, so panting is how animals cool. Or you can even watch a lizard, a lizard also does what's called Guller pumping. It'll, it'll actually, you know, that's how it cools itself down. Watch a li- a lizard will run and it'll, it'll basically pant and then it'll run again and it'll pant and it'll run again because it's prevent itself from overheating, right?

   8. SBSteven Bartlett21:25

      Mm-hmm.

   9. DLDaniel Lieberman21:25

      Now, what we did is we've, we have, uh, sweat glands. So most animals have, there's two kinds of glands, right? There's, one's called apocrine glands, those are the glands we have in our, you know, armpits and around our genitals, et cetera, or in our ears. They produce waxy, sort of fatty substances, right? Those are the ones that smell. Or, or ear wax that protects our ear. So all, most mammals have those apocrine glands. Eccrine glands are watery glands, and most mammals have them just on their palms, their paws and their feet, right?

   10. SBSteven Bartlett21:58

       Mm-hmm.

   11. DLDaniel Lieberman21:58

       So that they can... Just think about when you wet your finger, you can turn a piece of page, right? It gives you, it gives you more grip on something.

   12. SBSteven Bartlett22:05

       Mm-hmm.

   13. DLDaniel Lieberman22:05

       So when you're trying to escape from a predator, sweating on your hands will help you run up that tree.

   14. SBSteven Bartlett22:11

       Ah.

   15. DLDaniel Lieberman22:11

       If you're a mouse or something like that, a rodent. So most mammals have eccrine glands just on their palms, but in monkeys, um, they started to evolve having some sweat glands on their bodies, but not many. And so chimpanzees, monkeys have some eccrine glands on their bodies, but what we've done is we've increased that by an order of magnitude. We have like 10 times the number, uh, the 10 times the density of eccrine glands than monkeys and chimpanzees, and we lost our fur. So, and of course, fur prevents air from, from, you know, from convection of air next to the skin. So when you sweat on your skin and you don't have fur, the, uh, you, you can have evaporation of, of moisture, and then, and then air takes that away quickly, so you can keep evaporating moisture and then you can cool your body. So we've ef- effectively turned our entire bodies into a tongue essentially. And so we can dump amazing amounts of heat when we're physically active in hot environments. And that was obviously important for our ancestors, uh, when they're hunting, right? We have a huge advantage in the heat of the day because we can... Not only are we good at running f- for all, for, you know, because of our legs and our muscles and our Achilles tendon and all these adaptations we have for running, but we also have this incredible thermoregulatory ability to dump heat, which the animal we're chasing does not have, and we can, we can, we can, they'll, they'll die of heatstroke. But we don't know when that happened, and it's possible that, um, that our australopith ancestors before, uh, before hunting had started, 'cause remember, they are two-legged creatures, right? And they're not, um, they're not very fast. So maybe in the middle of the day when, when it was really, um, you know, hot, that was the best time for them to go out and get food because that's the time of day when carnivores that would love to chase them, right? If I'm a carnivore and I want to... Am I gonna eat a gazelle or an australopith, right? An australopith is going to be half the speed of the gazelle, that's easy pickings, right? So I'm gonna go for an australopith. So maybe our early ancestors-... foraged in the middle of the day when it was really hot, so that, because they, because they were too slow to run away from carnivores, and maybe that was an adaptation. And so the ability to, to, to dump heat effectively might have been really important for them. So it's possible, we just don't know, that sweating actually came before hunting. It's just simply, at this point we don't, 'cause skin doesn't preserve in the fossil record, we just don't yet

9. 24:38 – 30:10

   When did our brains get so big?

   1. DLDaniel Lieberman24:38

      know when that happened.

   2. SBSteven Bartlett24:39

      What about a big brain? Did that come before hunting or is that a, a product of the fact that we started hunting?

   3. DLDaniel Lieberman24:45

      It looks like more the latter, right? So our chimpanzees have brains, you know, a typical chimpanzee might have about a 400 cubic centimeter brain, like 400 grams. Think about it in grams, right? A typical human has a brain that's like 1,400 grams, so you know, really like three to four times the size of a chimpanzee's brain. For about five million years in our evolutionary history, so the earliest h- hominins, hominin is a term for a creature more closely related to us than a chimp, right? So the earliest hominins plus, you know, these australopiths like Lucy, they had brains that got up into the 500-gram range. Rarely, maybe sometimes it, 600, but not that much. Starting around two, two million years ago, brain size just starts to shoot up if you look on a graph, right? And that's of course around the time we started hunting, but it's, but it's really the time we have hunting and gathering, and so I think it's the whole system. It's, it's not just meat, although meat must have been an important component of it. But the whole hunting and gathering system is really a way to get more energy, right? Because you're, you're, you're processing your food, so you're getting more energy 'cause you're cooking your food or you're processing it in various ways. You're, you're cooperating, you're, you're, you're, you're, you're getting new sources of food such as meat and marrow and brains and whatever. All of that together means that more energy is available, and when more energy's available, then there's less of a constraint on brain size, because brains are expensive. Just right now, you and I, we're sitting, right? We're not really doing much of anything other than talking, but one out of every five of our breaths is to pay for our brain. Our brain is using 20% of our metabolism, right? And so to have a really big brain means you have to have a lot of energy available to you and it's so, so most animals can't afford big brains because they don't have enough energy, right? With hunting and gathering, you get more energy. More energy means selection can now, you know, the s- the cons- the, the, the constraints on having a big brain are now re- rel- released, and now you can get selection for a larger brain. So individuals with bigger brains might have had some advantage over individuals with smaller brains, maybe they were better at doing this, that, or the other, and so you get selection for larger and larger brain sizes, and it really accelerates up until, you know, well, it continues up until a few hundred thousand years ago when essentially brains reached basically modern size.

   4. SBSteven Bartlett27:07

      And then you get fat 'cause you have so much energy-

   5. DLDaniel Lieberman27:09

      (laughs)

   6. SBSteven Bartlett27:09

      ... and you have such a big brain. And so it's, it's-

   7. DLDaniel Lieberman27:11

      It's all about energy.

   8. SBSteven Bartlett27:13

      But that kind of makes sense, doesn't it? You store more energy and then we started to get fat?

   9. DLDaniel Lieberman27:19

      Well, fat is really important for a number of reasons. I mean, one of them is having a big brain. So, um, you know, a human infant, when it's born, its brain is consuming half its metabolic energy.

   10. SBSteven Bartlett27:30

       Mm-hmm.

   11. DLDaniel Lieberman27:31

       Like, when, when a kid is born, 50% of the m- of the e- of the energy it's spending is just to pay for its brain. It's a brain on a little body basically, right? And, um, and of course you can't stop feeding a brain. Brains require energy constantly, right? Brains don't store energy. They need a constant supply of glucose or, or ketone bodies which you can use as, when you don't have, uh, uh, sugar available to you, right? You can get those from fats, right? So infants, human infants are born unusually fat. A guy named Chris Kazawa showed that, you know, we, we know that a human baby when it's born is about 15% body fat. Way more than any other species, right? And that brain, that, all that fat is really t- uh, kind of an in- like money in the bank to make sure that that brain always has energy available to it. And furthermore, he published a really cool paper a few years ago which showed that when, uh, an infant's brain is growing, right, in the first few years of life, the f- when it's growing really fast, that's when its bo- body fat levels are going down. And when it's storing a lot of fat, that's when its brain isn't growing very much. So there's a trade-off in energy between fat and brains as we're growing. So, so big brains and f- fat bodies are intimately connected.

   12. SBSteven Bartlett28:45

       So we want to make sure our babies are fat.

   13. DLDaniel Lieberman28:47

       A fat baby is an e- essential, fundamental human adaptation. And, and the body fat that we have, I mean, a typical human has much more body fat than, than, than, than most animals. Most primates have about 4% or 5% body fat. Most mammals have about 4% or 5% body fat, whereas a skinny human has maybe 10% to 25% body fat, right? So that body fat is not only important for our brains, but it's also important for our reproduction because a typical mother nursing, for example, right, w- uh, hunter-gatherers will nurse for about three years. Nursing is really expensive. It costs about 600 calories a day to produce breast milk. Now imagine you're a hunter-gatherer and there's not a lot of food around, right? You're in what we call negative energy balance. You're not getting as much food in as you're spending, right? You can't just stop nursing. Your infant is still working to acquire that energy, so you draw down on your fat reserves, right? And so having all that fat, which goes up and down and up and down from season to season, you store more fat in the good seasons, you use that up in the bad seasons. Those are fundamental adaptations to keep us physically active, to enable us to reproduce the way we do, to pay for our big brains. They're, they're part of, you know, that, that, you know, our, our kind of relatively high level of fat and our, our predisposition to store fat is fundamental to our species. We wouldn't be here if our, w- if we didn't have all that

10. 30:10 – 38:46

    Why do we struggle to diet?

    1. DLDaniel Lieberman30:10

       fat.

    2. SBSteven Bartlett30:10

       And I guess this is why dieting is so hard.

    3. DLDaniel Lieberman30:14

       Right. Because well, we never evolved to diet. We evolved to put that fat on. We did evolve, of course, to use it when we needed it, right? But we never evolved, uh...... um, to- to- to get rid of fat. No, there was just- it was never a- you know, in an absence of obesity, there wouldn't be selection for- for that kind of, uh, physiological system, to lose fat without needing it.

    4. SBSteven Bartlett30:35

       'Cause when we try and diet, it does feel like our body's somewhat against us. When I hear about, like, sugar cravings, and you know, s- many people have told me that if you- the reason why diets don't work is because your body's trying to basically defend the weight that you're at, because that used to mean your- your survival.

    5. DLDaniel Lieberman30:49

       That's right. Um, we call that a starvation response, right? So when you s- go into negative energy balance, which is what a diet is, right? You're spending more energy than you're using, than you're taking in, (clears throat) your body goes into a- a starvation response. Your cortisol levels go up, for example, right? It's a- it's a- it's an emergency, right? It's like- it's- it's- 'cause cortisol is our stress hormone. Stress doesn't cause cortisol to go up. Cortisol goes up when we are stressed and it makes energy available to us, and one of the things that cortisol does is it makes us hungry, right? When you're really stressed at night, right? Studying for an exam, one of my students, right? They get, you know, hunger, you know, they get sugar cravings, right? 'Cause their cortisol levels, 'cause they're stressed 'cause I'm gonna give an exam in the next day, goes up and then they- they want energy, right? Cortisol also makes you store fat in visceral deposits, so- so- so belly fat, which is- which is ev- you know, concerning, right? It's a- it's a useful kind of fat, right? Uh, 'cause the fat that we store in and around our abdomen is- is very hormone sensitive. (clicks tongue) It's h- it's got lots of blood vessels, so that fat is a great energy supply when you're y- you know, you're physically active, right? When I- when I went running around Central Park this morning, right, I was burning some of my belly fat. But when cortisol levels go up, that's like, it also directs us to bos- deposit fat in those stores, right?

    6. SBSteven Bartlett32:07

       Mm-hmm.

    7. DLDaniel Lieberman32:08

       And the problem with those stores is that, um, they're also very inflammatory. So when those fat cells get too large and they swell, they become dysfunctional and they cause inflammation. They cause chronic systemic inflammation, which is just ruinous for our health. It causes diabetes and Alzheimer's and, you know, heart disease, all kinds of diseases that, um- that, um, pretty much every major disease that we're worried about. The mismatch diseases that we often talk about are, you know, many of them are- are stre- are inflammation related and- and- and- and, uh- and that's why we're conc- people are concerned about excess, uh, adiposity, excess fat, because excess fat causes inflammation.

    8. SBSteven Bartlett32:50

       (clicks tongue) So that means that people that are more stressed are more likely to have belly fat.

    9. DLDaniel Lieberman32:54

       Correct. Yes, that's true. So s- that's one of the reasons why stress is, you know, a r- a risk factor for so many diseases. Psychosocial stress is a- is a- it has pernicious effects, and that's why, you know, racism, discrimination, all those- all those factors that can elevate stress, commuting, um, um, have negative health consequences because it- it causes us to- our cortisol levels to go up. It causes our- us to- us to put fat in the wrong places. It has a- uh, cortisol also turns your immune system down. Cortisol has all kinds of, you know, negative effects when it's- when it's long term and persistently high.

    10. SBSteven Bartlett33:36

        It's often been said that if you lose too much weight, for example, if a woman loses too much weight, then her menstrual cycle will stop. And I was thinking about this from an evolutionary perspective, and you were s- saying how, you know, fat is essentially evidence of our survival. So in some ways, is that our ... If that is true, then is that our body basically stopping our menstrual cycle to conserve energy? Basically, if you could think about it like our body saying to us, "We don't have the energy to have kids right now."

    11. DLDaniel Lieberman34:06

        (clicks tongue) You are absolutely right. So it's a little bit comp- more complicated than that, but- but you- you basically got it right. So there's two things. First of all, fat is not just an energy store. Fat is also an organ, right? Fat- fat, uh, produces hormones. We produce- your fat produces a hormone called leptin, which affects appetite, but it also produces, um, estrogen. So, uh, when women have very low levels of body fat, their estrogen levels decline, um, and they don't produce enough estrogen to have effective menstrual cycles. Um, so they become what's called amenorrheic. Amenorrhea is- is a- is, uh, just a fancy medical term for- for, um- um, for loss of, uh, sort of normal cycling. It's been shown by many researchers, a former professor of mine, uh, Peter Ellison and there are other researchers around the world, a woman named Grazyna Jezierska in Poland, others have shown that, you know, our bodies are incr- incredibly, uh, sensitive to energy availability. For example, women who are dieting, they may have plenty of body fat, but when they're dieting, which means they're going into negative energy balance, levels of progesterone, which is a very important hormone for the menstrual cycle, progesterone is produced in the second half of the menstrual strike and it maintains the- the uterine lining so that you can have implantation. Progesterone levels plummet, they go down by, you know, 50% during the luteal phase, that second half of the menstrual cycle, uh- um, thereby decreasing, um, their ability to conceive. Um, uh, women who are very physically active also, there's a decrease in the amount of progesterone, again, during the second half of the menstrual cycle. And a flip way of thinking about it though is that, because remember, what we evolved to do is to have as many offspring as possible, and so our bodies also ... Another way of thinking about this also is that, uh, whenever there's extra energy available, the body, you know, it's an adaptation to say, "Hey, let's use that energy for reproduction. So let's increase estrogen levels, let's increase progesterone levels so we can increase our- our fecundity, increase our fertility." So, you know, there's a bit of a-

    12. SBSteven Bartlett36:13

        A balancing act?

    13. DLDaniel Lieberman36:14

        Yes, it's a bit of a balancing act. So, to s- so obviously, you know, exercise is not bad for women who are trying to conceive, and, and, and women who are... but women who are sedentary and aren't exercising have high levels of estrogen and progesterone, and that may, that may be one of the reasons why physical activity decreases the risk of breast cancer so much. So, women who are physically active have like a 30% to 50% lower rate of breast cancer, and p- a lot of that, part of that has to do with the fact that their hormone levels are more normal, because sedentary women have abnormally high levels. But nonetheless, it's the, the important point from what you asked is that our, the body is incredibly sensitive to energy, right? And so it knows that when energy levels are low and you're losing fat, this is not a good time to invest, because think about it, pre- pregnancy lasts nine months, it's incredibly expensive. Then you're gonna be spending months later nursing, which is also very expensive. Maybe this is not a good time to invest. Let's wait until times are better, then you know that this is a, this is a, a better use of your, of your, of, you know, a better time to get pregnant, a better, you're gonna have a much more likely positive outcome.

    14. SBSteven Bartlett37:20

        I was thinking about what you were saying through the lens of stress as well, because stress releases cortisol. And if someone is incredibly stressed, I imagine they're gonna have trouble with fertility a- as well.

    15. DLDaniel Lieberman37:32

        Yep.

    16. SBSteven Bartlett37:32

        Probably for the same reason. I guess it's like a lion was running at you, this is not a good time to have a-

    17. DLDaniel Lieberman37:36

        (laughs) S- Cortisol, cortisol, one, one of the things that cortisol does is it turns down everything that you don't need to do at that moment in time, right? Because we evolved to elevate cortisol acutely, you know, for short bursts when, you know, when, when the lion comes into the room, right? Um, but, but not over very, very long periods of time. So, you know, when, when a, when the lion comes into the room, this is not a time to reproduce, it's not a time to spend energy on your immune system, it's not a time to do all kinds of stuff, right? Just run, right? Make e- energy available. But situations where you have pr- where, persistently high levels of cortisol.

    18. SBSteven Bartlett38:09

        Chronic stress.

    19. DLDaniel Lieberman38:10

        Chronic stress. That's what we call a mismatch, right? Mismatches are conditions that, um, for which our bodies did not evolve, right? These are novel, environmental conditions, um, for which we are inadequately or imperfectly adapted for, and that they cause the vast majority of the diseases and problems that we, we encounter today. And, you know, taking exams is a, is a mismatch. Um, having, you know, r- you know, discrimination, racism, poverty, um, these are, you know ... And all those sorts of things that elevate our cortisol levels for long periods of time, those are mismatches.

11. 38:46 – 42:56

    Modern-day mismatched diseases

    1. DLDaniel Lieberman38:46

       You know, in fact, the vast majority of the diseases that people have today, um, apart from some infectious diseases, but the vast majority even of infectious diseases are mismatches because they come from humans spending more time with animals and, like, all, all the, a lot of the diseases that we, you know, infectious diseases that we have actually are diseases that jumped over from the animal world to, to humans. Tuberculosis, for example, right? Um, that's a disease that hunter-gatherers didn't get. It's a, it, it came after farming.

    2. SBSteven Bartlett39:13

       The vast majority of diseases?

    3. DLDaniel Lieberman39:16

       I would say so, yeah. I mean, heart disease. I mean, look, we, when we look around the world and look at people who don't live in, you know, modern or Western lifestyles, they, they ... Heart diseases is rare to nonexistent. There's a wonderful study of a, of a group of people in the Amaza- in the Amazon called the Tsimane. Th- these are horticulturalist foragers, right? They have, there's like no evidence whatsoever of any coronary heart disease in these people. Some of the populations that we've studied, no hear- no increase in blood pressure. In fact, back in the 1970s, some of the first studies that were ever done on the health of hunter-gatherers found that 80-year-old hunter-gatherers in the Kalahari had the same blood pressure as 20-year-old hunter-gatherers in the Kalahari. Whereas ... And they compared them to, to, to, to, a- to English, um, people in, you know, Londoners at the same time, and of course, by the time you're 70 or 80 in London, almost everybody's hypertensive, right? This is, this is a, this is because of diet and physical activity and, and probably also stress. Um, these, uh, these are, these are things that have changed in our modern world for which we are very poorly adapted.

    4. SBSteven Bartlett40:20

       No diabetes?

    5. DLDaniel Lieberman40:23

       If it exists, nobody's diagnosed it. It's probably incredibly rare. But even a few generations ago, diabetes was rare. I mean, diabetes is the world's fastest growing disease. W- where I work in Kenya, um, in, uh, in the area around a town- city called Eldoret. When I first started working there, gosh, long time ago, you know, you'd drive into the city, and you'd be in Eldoret. Now as you drive into the city, you pass by all these diabetes clinics. They, they weren't there before. That's because diabetes is rising in, in, in Africa ju- to, at incredibly rapid rates, which, you know, isn't s- surprising, 'cause diabetes in places like the United States and England are incredibly common. About something like 12% of Americans have diabetes now.

    6. SBSteven Bartlett41:09

       You said that this mismatch is responsible for most diseases. Doesn't that therefore mean that I'm most likely to die from a mismatch disease in my life?

    7. DLDaniel Lieberman41:17

       Yes.

    8. SBSteven Bartlett41:18

       Okay.

    9. DLDaniel Lieberman41:19

       Yes. The vast majority of us in, in the Western world will die from a mismatch disease. The number one disease in the world today that kills more people than anybody, uh, anything else is, is heart disease. And as far as we're con- you know, heart diseases kills at least about a third of us. Cancer is number two. Cancer is of course an ancient disease, so not all cancers are mismatch diseases, but many cancers are mismatches, right? Breast cancer, which is much more common in Western populations than in non-Western populations. Um, but heart disease is, you know, is essentially as far as we're concerned nonexistent, uh, until fairly recently.

    10. SBSteven Bartlett41:54

        And now it's killing about 33% of us, 30... You said a third, right?

    11. DLDaniel Lieberman41:57

        Yes.

    12. SBSteven Bartlett41:58

        That's crazy. It's so, so crazy.

    13. DLDaniel Lieberman42:00

        Uh, that's the bad news, right? But the good news is because they're mismatch diseases, they're not, they're not inevitable, right? We shouldn't just say, "All right. Heart disease kills a third of us. Let's just, um..." W- because the, the amazing thing about heart disease is that diet and exercise...... can prevent a large percentage, if not almost the m- almost all of them, right? If people who live in environments where they don't eat obesogenic diets, diets that are, that make people overweight, diets that lead to metabolic syndrome, diets that are, uh, that are atherogenic, that cause ather- atherosclerosis, right? People who are physically active, um, and stress is also an important, uh, role, plays a role in heart disease, don't smoke, um, have vastly lower rates of heart disease to the extent that it's, you know, this is a, this is a, this is a disease that doesn't have to exist.

12. 42:56 – 45:17

    Why did you write a book about food?

    1. DLDaniel Lieberman42:56

    2. SBSteven Bartlett42:56

       You said you're writing a book about diet and food.

    3. DLDaniel Lieberman42:59

       Yes.

    4. SBSteven Bartlett43:00

       Why?

    5. DLDaniel Lieberman43:01

       The story of how the diets that we eat today and, and, uh, is, is actually a really fascinating story. But also, um, because I think that we, um, uh, if we take a, a more evolutionary approach to diet, um, we can, I think, do much better to thinking about, you know, uh, how people make choices. I mean, one important point to make is that, you know, today, like, when I'm, we fin- finish this interview and I'm gonna go home and my wife and I are gonna, and my daughter and my mother-in-law are gonna tr- try to decide what we're gonna have for dinner tonight. Right? And we can, like, we can go, we can eat whatever we want, right? We can go to the supermarket and there's like, you name it, right? Here in New York there really is you name it, right? We can, we can go out to restaurants. We can have Chinese or food, or Japanese food, or American food, or French food, whatever, right? We have w- we have incredible choices to us. For most of human evolutionary history, people never chose what they ate ever, right? They ate what was available to them. And now with all this choice, we... Comes, comes, comes bad choices, right? And so, uh, I would like to help people figure out how... Not only realize that these choices that we have to make are, were not really evolved to do, but also how to better understand what those choices are and what the complexities are of, of them. 'Cause there are n- there, there's no such thing as a free lunch, right? Every, every choice that you make has alternatives and alternative consequences, and, and I think people oversimplify diet. People come up with simple ideas how, you know, just do this, just be a vegan, just be a this, just be a that. Um, there are no perfect answers.

    6. SBSteven Bartlett44:39

       Do you think in some ways that our culture moved so much faster than our biology in a sense? Because we're, like, super sedentary now. We just sit all day. We have these screens that bring us our food. Um, the food is processed. And is this part of what's causing this sort of misalignment or these mis- mismatched diseases, as you call them, is...

    7. DLDaniel Lieberman44:57

       Absolutely. Because evolution by natural selection occurs really slowly, right? Every generation, people with genes that have, give them adaptations that are better able to handle a particular environmental context do better than the next generation. So slowly, slowly, slowly, generation by generation,

13. 45:17 – 46:30

    Has our culture moved too fast?

    1. DLDaniel Lieberman45:17

       you get change, right? And that's true for every animal, right? Um, ah, mismatch is not unique to humans, right? As environments change, some animals are better adapted to that environment than other animals, and tho- those animals are gonna be more likely to pass those genes on to their offspring. So mismatches are part of the natural selection. Every species, as environments change, is subject to mismatch, or as they move into new environments. The difference with humans is that we have culture, and culture has caused an acceleration of environmental change, right? Think about, I mean, just today, right? I have now a, in my pocket a, a computer, right, that I didn't have a few, you know, decades ago, right? Um, we have internet and email and all kinds of things, right? Our, our... I- just the last few decades, the world has changed amazingly. Just think about the last few generations, the last few hundred years, the last few thousand years. So cultural evolution is so powerful and so rapid, it's so fast, it's so transformative, that we have m- made our world so fa- vastly and rapidly different that our bodies cannot possibly keep up in terms of our biology. It's this mismatch, it's this difference between evolutionary biological change and cultural change that has heightened the kinds of mismatches

14. 46:30 – 50:28

    We've decided to live with diseases rather than prevent them.

    1. DLDaniel Lieberman46:30

       that we exist. And then guess what we do? Right? So we... Let's say we... I'll give a very simple example, right? Until recently, nobody read, right, and nobody spent a lot of time indoors, and so myopia used to be extremely unusual, right?

    2. SBSteven Bartlett46:42

       What's that?

    3. DLDaniel Lieberman46:43

       Myopia is having, is being nearsighted.

    4. SBSteven Bartlett46:45

       Okay.

    5. DLDaniel Lieberman46:46

       So if you go to, like, there's a famous study where they looked in, in, uh, in Inuit populations, right, in Alaska, and they looked at grandparents and grandchildren. The grandparents all had perfect vision and the grandchildren all need glasses (laughs) , or at least a large percentage of, like 30% of them, right? In various parts of the world, the pre- the pre- the number of people who are, are nearsighted has gone up. In some parts of the world, it's 50%. In, in America and England, it's probably about 30% of us need glasses. But this is all recent. Um, the, uh, in fact, the first study of this was done on the Queen's Guards, you know the... Or actually now they're the King's Guards, right? So you know those, those... They have the-

    6. SBSteven Bartlett47:20

       Yeah.

    7. DLDaniel Lieberman47:20

       ... bear skin hats? I don't know what kind of-

    8. SBSteven Bartlett47:22

       Neither do I.

    9. DLDaniel Lieberman47:23

       ... fur is on their heads.

    10. SBSteven Bartlett47:24

        (laughs)

    11. DLDaniel Lieberman47:24

        But anyway, they're the ones who stand in front of Buckingham Palace, right? There was a study done in the, in the early 1800s which showed that, um, it was the officers who had a higher percentage, the, like a large number of the officers had to wear glasses, but the, but the, the foot soldiers were all fine. Um, and there was something about it, right? The- that, about the officers. And then people started studying them around the world, and, and, and then, uh, initially it was thought to be reading, and now we know from more careful studies that it's really spending a lot of time indoors when you're young that causes myopia. So we never evolved to do that, right? So we're more prone to myopia. But it's not a big deal because guess what? We just go to the optician and we get glasses and we can deal with it and, you know, it's not... doesn't really have really any major effect on our, on our he- on our health or our longevity, our ability to find a mate, et cetera. We all do just fine.

    12. SBSteven Bartlett48:15

        Can we undo it?

    13. DLDaniel Lieberman48:16

        Well, here's the thing. I mean, we- what we're doing in... Now, myopia, you, there, you can get LASIK surgery and there are some things you can do, very expensive, most people can't afford it, right? But-... the point is that we're treating the symp- when, when you get glasses, you're treating the symptom, not the cause, right?

    14. SBSteven Bartlett48:32

        Mm-hmm.

    15. DLDaniel Lieberman48:33

        But it's okay, right? Because it's just glasses, right? The problem is that for many mismatched diseases, right? When we, still, we're treating the symptoms rather than the causes, right? So-

    16. SBSteven Bartlett48:45

        Cancer.

    17. DLDaniel Lieberman48:45

        Cancer, right. Or, or, or many forms of heart disease, right? You don't see a doctor in our, in our, in our medical system until you get sick, right? And then you get pills to lower your blood pressure and pills to lower your cholesterol, et cetera. But, but these aren't... Uh, well, those, some of thems can be preventative. But, but, um, but to a large extent, most of medical treatments are treating the symptoms of diseases after they occur. And I'm gonna... And of course we should do that. We should alleviate pain, we should alleviate suffering. We should try to decrease people from, you know, dying from all kinds of diseases. But wouldn't it be better if we actually prevented those diseases in the first place, right? We would have a much more effective medical system. So what we're causing, in my opinion, kind of a new form of evolution. I call this dysevolution, whereby we're treating the symptoms of mismatched diseases, thereby pro- enabling the- those diseases to remain prevalent, right? And in some cases get worse because, because we can now cope with them, right? So people now get diabetes, we give them metformin or whatever, various kinds of drugs. They get, they get heart disease, we give them various, you know, you know, pills to kind of keep them going. They get myopia, we give them glasses. All of these are, are, are, are things we should do. But wouldn't it be better if we prevented people from getting heart disease in the first place, right?

    18. SBSteven Bartlett50:05

        'Cause this is one of the big questions I always have with evolution, and when we're talking about our evolutionary history, is, is are we still evolving? And from what you said there, it sounds like we, in a way we are, but it doesn't sound good. It sounds-

    19. DLDaniel Lieberman50:15

        (laughs)

    20. SBSteven Bartlett50:15

        ... as you say, de-evolution. Sounds like we're in some ways-

    21. DLDaniel Lieberman50:18

        Dysevolution, yeah. Yeah.

    22. SBSteven Bartlett50:20

        ... dysevolution.

    23. DLDaniel Lieberman50:20

        Yeah, I mean, I mean there is, there is a little bit of selection going on. I mean, (coughs) you can't stop selection. It's like gravity. It happens, but it's slow.

15. 50:28 – 53:17

    The modern foods we eat have affected the way we look.

    1. DLDaniel Lieberman50:28

    2. SBSteven Bartlett50:28

       What we eat and how we eat, um, I think it was James Nestor that said, "The way we chew impacts what our face looks like when we become adults." If a baby's chewing lots of soft foods, when they grow up, they're gonna have like a small jaw.

    3. DLDaniel Lieberman50:39

       Yeah, that's research I did actually. Yes. (laughs)

    4. SBSteven Bartlett50:40

       Oh, really? I think he cited you. (laughs)

    5. DLDaniel Lieberman50:42

       (laughs) Um, yeah, so, so how you, your chewing affects the, the shape of your, you know, how your, your jaw grows. Um, and so it is true that we have smaller jaws today than we used to. The good news is it's not that bad, right? It doesn't really cause that much... You, maybe your teeth are, you know, more likely to have malocclusions, et cetera. But, you know, you can, but we can go to the orthodontist and have our third molars extracted, et cetera. I mean, we can, we can cope with that, right? It's not, um, it's... That's not the worst thing, right? Of course he thinks that it causes us to breathe through our mouths and all that sort of stuff. Um, but it's not the kind of disastrous sort of, um, mismatch that occurs from say, you know, uh, well this is controversial, but, um, the, the evidence, you know, the vast majority of the evidence suggests that if you eat a lot of sugar and you eat a lot of saturated fat, you're more likely to get heart disease, you're more likely to get plaques in your arteries, right? If you don't, aren't physically active, you're, you know, do exercise or, or physical activity, your, your blood vessels start stiffening and you start becoming hypertensive, right? Uh, these are all, um, these are all aspects of our environment that, um, that we, we have the potential to, to, to control better and to prevent disease.

    6. SBSteven Bartlett51:54

       Do you think we've got into a bit of a bad habit as a society of just throwing a, a pill at the problem?

    7. DLDaniel Lieberman51:59

       Yes. I mean that's, that's the fundamental argue- argument I'm making about dysevolution that, that, you know, it's just, it's expedient to treat the symptoms of a problem rather than its cause. And-

    8. SBSteven Bartlett52:09

       What's the problem with that?

    9. DLDaniel Lieberman52:11

       Well, because... f- number of reasons. One is, it's... Isn't the... The best disease is the one that you never get in the first place.

    10. SBSteven Bartlett52:19

        (laughs)

    11. DLDaniel Lieberman52:20

        So, so we can keep people alive once they get heart disease. We can keep people alive once they get arthritis. We can keep people alive once they get all kinds of diseases, but they, but their, but their quality of life goes down. And of course we pay for it, we pay for it out the nose, right? It's something like 70%, 80% of the time when somebody goes into a doctor's office, that's for a preventable disease, 70%, 80% of the time, right? That's a, an astonishing amount of money that we spend in our medical system on essentially mismatched diseases.

    12. SBSteven Bartlett52:51

        Mm-hmm.

    13. DLDaniel Lieberman52:51

        It's bankrupting us, but it's also causing misery. And, um, it differentially affects people of, of low income and people who are, uh, suffer from discrimination. Um, I mean, look in the United States, right? Who gets the chance to exercise and eat, you know, fresh vegetables and, you know, high quality foods and non-processed foods? It's, it's wealthy people, right? So it's also, it's just unfair and unjust.

16. 53:17 – 58:49

    Is cancer a consequence of our modern society?

    1. DLDaniel Lieberman53:17

    2. SBSteven Bartlett53:18

       You mentioned cancer. In w- in what way and how do we know that if that's a mismatched disease?

    3. DLDaniel Lieberman53:23

       Well, cancer is not completely a mismatched disease. I mean, you know, all species that are multicellular get cancer. Cancer is a, is essentially a disease of evolution going wrong, right? Natural selection going wrong, right? So instead of, you know, when you have many different kinds of cells in your body, when a cell becomes essentially selfish and starts to out-compete other cells because of mutations it gets, that's a cancer, right? So cancer is an outcome of multicellularity. Dinosaurs got cancer, right? We have evidence for bone cancer in dinosaurs. Um, so it's... We're never gonna get rid of cancer completely, but we also know that cancer is very much a disease of energy, right? When, when people move to high energy environments, they're much more likely to get cancer.

    4. SBSteven Bartlett54:10

       More food, eating more.

    5. DLDaniel Lieberman54:11

       More food. Physical inactivity is a major risk factor for cancer. Um, insulin, for example, high levels of insulin. Insulin, you know, promotes, um, you know, anything that promotes mitogenesis, you know, which is mutation, you know, uh, cells to divide, um, um, is going to increase rates of cancer. Um, also anything that increases the rate of...... of, of, you know, the, a lot of the cells that c- get cancer are cells in our bodies that interact with the outside world. So our lungs, our guts, you know, c- our colons, where, you know, things from the outside world-

    6. SBSteven Bartlett54:43

       Skin.

    7. DLDaniel Lieberman54:43

       ... come into contact with them. Skin, exactly. Those are cells that often get cancer. So when we have carcinogens, you know, poisonous, toxic compounds in our environment, those can elevate levels of cancer. So smoking, car pollution, et cetera, those can cause cancer. But also having lots of energy. So we talked earlier about when women are physically inactive their, their hormone levels shoot up, right? Because the body says, "Ha ha, more energy. Let's spend it on reproduction," right? And there's a trade-off there. More en- the higher levels of estrogen and progesterone increase the rate of, of breast cancers that, that occur. Because, because they cause more, more turnover in those cells in the, in breast tissue. And that's, that's why those, those cancer rates are higher. So you can... There's famous studies which show that. You look at women from Bangladesh who live in Bangladesh, women from Bangladesh who move to England, or Bangladeshi women who are born in England and live in England. Wherever you... When... No matter how you, how you look at it, Bangladeshi women who move to England, their cancer rates go way up. The difference? A major difference is energy. You know, the diet that they have, the physical activity levels they have. They-

    8. SBSteven Bartlett55:52

       They're eating more, they put on more weight.

    9. DLDaniel Lieberman55:53

       Cancer rates just shoot up. Cancer... So if you could actually plot GDP of countries against cancer rates, it's almost nearly a straight line. Uh, uh, the richer the country, the higher the rate of cancer.

    10. SBSteven Bartlett56:03

        What about hunter-gatherer women, did they have less, um, ovarian cancer?

    11. DLDaniel Lieberman56:08

        Oh, yeah. That's a hard thing to measure because diagnosing cancer requires some sophisticated technology. And to my knowledge nobody's ever done careful studies of cancer rates among hunter-gatherers. Um, but most of us are pretty convinced that cancer rates are much, much, much lower among hunter-gatherers. But again, also the, the population sizes are tiny, so you can't really get very large samples.

    12. SBSteven Bartlett56:31

        The amount of menstrual cycles you have.

    13. DLDaniel Lieberman56:33

        Is a major factor, right? So I believe, I'm... I hope I get the numbers right. A typical woman today who goes through her entire reproductive lifespan will have something like 500 menstrual cycles because of birth control and, um, um, and smaller families. And s-

    14. SBSteven Bartlett56:48

        It says 350 to 400 in your book.

    15. DLDaniel Lieberman56:50

        Is that what it says?

    16. SBSteven Bartlett56:51

        Yeah. (laughs)

    17. DLDaniel Lieberman56:51

        Okay. Thank you. Okay. Um, it's, uh, it's in the hundreds, right?

    18. SBSteven Bartlett56:55

        Yeah.

    19. DLDaniel Lieberman56:56

        A typical hunter-gatherer is gonna have something like 50.

    20. SBSteven Bartlett56:59

        50?

    21. DLDaniel Lieberman57:00

        Yeah. In her entire life.

    22. SBSteven Bartlett57:02

        Wow.

    23. DLDaniel Lieberman57:04

        And every time you go through a menstrual cycle your, your body is being exposed to high levels of these hormones, right? Birth control, um, and sort of modern family planning, which, you know, I'm not obviously, um, I, uh, opposed to it, but it is another factor that has probably elevated rates of breast cancer.

    24. SBSteven Bartlett57:22

        I didn't... I never knew that. I never knew that having more cycles reduced your (overlapping)

    25. DLDaniel Lieberman57:28

        Well, 'cause each cy- every cycle involves, you know, surges of hormones. That's what causes the cycle. First you have an estrogen surge, then you have a progesterone and an estrogen surge.

    26. SBSteven Bartlett57:40

        Ah, of course. Uh, yeah.

    27. DLDaniel Lieberman57:40

        That's, that's what happens across the menstrual cycle.

    28. SBSteven Bartlett57:44

        Uh-huh. And hunter-gatherer women would've been pregnant more often, more of their life?

    29. DLDaniel Lieberman57:48

        Well, yeah, they... A typical, what we call a natural fertility population, a population that doesn't use birth control, women are most of the time pregnant or nursing. And they go through short periods when they, um, are doing neither and then get pregnant again. So, so the number of... And, and you don't, of course, have menstrual cycles when you're pregnant, and you generally don't have menstrual cycles when you're nursing until, again, it's your energy level. So, so because nursing costs so much energy, that high energy demand of nursing suppresses ovarian function. So p- and so, so, so nursing women are often amenorrheic. They're not cycling.

    30. SBSteven Bartlett58:28

        And that's not just ovarian cancer, that's breast cancer as well. That's-
17. 58:49 – 1:05:38

    How our bodies store energy

    1. DLDaniel Lieberman58:49

    2. SBSteven Bartlett58:49

       I wanted to talk about how our body stores energy, 'cause I think that in part, uh, answers a lot of these questions around, um, the things we're discussing about weight loss, about diet, about all those things we've talked about previously. I have a very loose understanding of this, so please enlighten me. But I did go keto for eight weeks-

    3. DLDaniel Lieberman59:07

       (laughs)

    4. SBSteven Bartlett59:07

       ... and I lost so much weight. It's am- uh, it's pretty crazy. It bounced straight back, of course.

    5. DLDaniel Lieberman59:11

       Of course.

    6. SBSteven Bartlett59:11

       (laughs) Yeah.

    7. DLDaniel Lieberman59:12

       'Cause you mostly lost water.

    8. SBSteven Bartlett59:13

       Oh, really?

    9. DLDaniel Lieberman59:14

       Yeah.

    10. SBSteven Bartlett59:14

        Ah.

    11. DLDaniel Lieberman59:15

        That's one of the problems with, uh, m- many diets. So, so fat is a, is a... Fat is a wonderful molecule, right? It's... We, we tend to demonize it, but it's, it's... Fat is life, right? Fat is a really important molecule. So a fat is a, is a... A fat molecule has a backbone of something called glycerol. Glycerin, right? It's a three carbon molecule. There's a th- carbon, carbon, carbon, and there's sti- a little hydrogen sticking off. And to each one of those carbons is a chain, uh, sticks off a chain of what's called a fatty acid. So, so they're called triglycerides. They're three fatty acids on each glycerin. And, and there are different kinds of fatty acids. Like, there are saturated fatty acids and unsaturated fatty acids, and we can talk about all those, whatever. But the point is that these are... Each fatty acid stores a huge amount of energy, because those long chains of carbon, what our body does is it cleaves those carbons into smaller units and gets... And we get energy from the, from the bonds between those carbons. That's basically what our mitochondria are doing, right? So fatty acids, fats in general, have, store a huge amount of energy. They store twice as much energy as carbohydrates per unit mass. So what we do is we, we eat foods that have fat in them, or we eat carbohydrates and our livers convert them quickly to fats. It's not... It's, it's easy, right? So that's why, you know, fat free-

    12. SBSteven Bartlett1:00:36

        Annoying.

    13. DLDaniel Lieberman1:00:36

        ... diets don't prevent people from becoming fat, right? Often with the help of insulin, but it's not the only hormone involved. We then... We want to store those. If you're not burning them, right? Our body can either burn them or store them-So, if we're not burning them, i.e. we're running or gesticulating-

    14. SBSteven Bartlett1:00:54

        Mm-hmm.

    15. DLDaniel Lieberman1:00:54

        ... talking, et cetera, um, um, w- we, we're gonna store them, and we store them in, in special cells called adipocytes. Those are the fat storing cells, and our bodies have billions of them. You're born with billions of these, but you only have so many adipocytes. You get them when you're young, when you're born, and that's it. That's the number of adipocytes you have for the rest of your life. And so, and so those adipocytes... So, insulin, for example, helps potentiate the movement of triglycerides, right, uh, um, which, which you wanna break down, and then you transport them into the fat cell, and then you reassemble those fats in the fat cell, you know, the- the- the glycerins and the fatty acids. You reassemble them in the fat cell, and they swell like a balloon. So, every little fat cell in your body is like a little balloon filled with, with fat, and, um, and it's there to be used. And then there are hormones which then help us retrieve that fat when we need it, right, when we're running a marathon or g- or just sitting around talking and without having had lunch for a while or whatever.

    16. SBSteven Bartlett1:01:51

        (laughs)

    17. DLDaniel Lieberman1:01:52

        Um, and so, you know, we, we store fat. We r- we then burn fat, we store fat, we burn fat, we store fat, we burn fat, et cetera, and that's normal, right? And as I s-... As we talked about earlier in this conversation, humans evolved to have an unusually high level of fat. So, a typical hunter-gatherer male will have about 10 to 15% body fat. A typical hunter female will have about 15 to 25% body fat. That's a normal sort of skinny human being. That's way more than most mammals, right?

    18. SBSteven Bartlett1:02:17

        So, women have more?

    19. DLDaniel Lieberman1:02:19

        Women have more, right. So, women have a higher, uh, uh, percentage of body fat, although actually, women tend to be smaller bodied, so the total amount of fat that men and women store is about the same.

    20. SBSteven Bartlett1:02:31

        Mm-hmm.

    21. DLDaniel Lieberman1:02:31

        Women, of course, if you think about it, um, because they're involved in... Th- they're the ones who have to pay for reproduction, directly, either during pregnancy or, or nursing, that fat is especially important for reproduction, right?

    22. SBSteven Bartlett1:02:45

        Mm-hmm.

    23. DLDaniel Lieberman1:02:45

        So, what happens is that tho- that fat is there, and it's like a bank account, right? It's energy that we store and energy that we use, and we store it in different places. Most of the fat that we store is what we call subcutaneous, so underneath the skin, subcutaneous. But we also store fat that we call ectopic. That's outside of where it should be. Some of that fat is... A- and a lot of that, that ectopic fat is, some of that's in our liver. We call that, um... So, people have a lot of... So, normal livers have just a little bit of fat in them, but if you have too much fat in your liver, your liver starts to malfunction. That's called non-alcoholic fatty liver syndrome. You can have fat around your kidneys. That's what suet is, right? But too much fat around your kidneys, again, causes problems. Fat around your heart, fat around... So any of... All that fat in your, in your, i- in your abdomen, that, we call that visceral fat. Viscera means guts, right? So, that gut fat is, is, is very problematic and all, uh, because when those fat cells get too big, so if you store a lot of fat b- beyond those sort of normal levels, as the fat cells get bigger and bigger and bigger, just like any balloon, they start to rupture. So, you know, if you overfill a water balloon, it's gonna break.

    24. SBSteven Bartlett1:03:53

        Mm-hmm.

    25. DLDaniel Lieberman1:03:53

        If you overfill an adipocyte, it's also gonna start break. And when it starts to break, it attracts the immune system, and the immune system comes in, white blood c- cells come, right? They're, they're, they think something's wrong. You have a... We have, we have damage here. And they start to produce molecules that trigger a, a, a system-wide immune response, right? And this... And the fat cells themselves, also, will trigger an immune response. The fat cells can produce the same kinds of molecules that our white blood cells produce. So, the wh- white blood cells are produce molecules called cytokines. Cyto for cell, right? Kine for, you know, enzymes that do something, right? They... And, and so the ones that fat cells produce, we call them adipokines.

    26. SBSteven Bartlett1:04:38

        Mm-hmm.

    27. DLDaniel Lieberman1:04:38

        And like, one adipokine that it produces called... Is it TGF-alpha, right, you may have heard of.

    28. SBSteven Bartlett1:04:44

        Mm-hmm.

    29. DLDaniel Lieberman1:04:45

        And that turns on your... It's like a... It's like turns up the dial on your, on your, on your inflammatory system, right? And it goes everywhere in your body, and you start getting inflammation, right? And that inflammation, for example, if it's h- those turns... So if you're... If you have inflammation in your, in your blood vessels, then that inflammation can help cause plaques to form in your arteries. If that inflammation occurs in your brain, those can cause plaques in your brain that can cause Alzheimer's. If that inflammation affects, um, uh, receptor cells on muscles, et cetera, that can cause insulin resistance, which can cause diabetes, a- and the list goes on, right? So that, that chronic inflammation, which can be caused by too many fat cells that are overpacked, essentially, is, is why too much fat, uh, can, can be... Can cause health problems.

18. 1:05:38 – 1:09:59

    The keto diet and fasting

    1. DLDaniel Lieberman1:05:38

    2. SBSteven Bartlett1:05:38

       The keto diet and fasting, they... Uh, someone said to me the other day that keto is basically a form of fasting, in a way. Um, and are they... How do they help the body? Because people are pretty crazy and pretty keen on both fasting at the moment, but also the ketogenic diet.

    3. DLDaniel Lieberman1:05:54

       Well, fasting is when you go into negative energy balance, right?

    4. SBSteven Bartlett1:05:58

       Which is how we spent most of our sort of evolutionary history, right?

    5. DLDaniel Lieberman1:06:01

       Well, it's how you spend part of every day, right? We, we eat. (laughs) After you eat, you're in positive energy balance.

    6. SBSteven Bartlett1:06:08

       Mm-hmm.

    7. DLDaniel Lieberman1:06:08

       And then when you... In between meals, your energy balance goes down, right? Now you're in neg- you're burning now energy that you've stored. When you're asleep, you're in negative energy balance. So, fasting is just a prolonged state of negative energy balance, right?

    8. SBSteven Bartlett1:06:20

       Does that mean that would... It would reduce my chance of getting cancer?

    9. DLDaniel Lieberman1:06:23

       Could do. People are, are hoping that's the case. I don't know how good the data are for intermittent fasting, um.

    10. SBSteven Bartlett1:06:30

        Because if the surplus in energy causes cancer, then me being in that negative energy balance presumably will reduce my chances of getting these.

    11. DLDaniel Lieberman1:06:37

        Right, but then you have to go back into positive energy balance at some point too, right? You can't keep up negative energy balance. So, intermittent fasting isn't necessarily a way to lose weight if you eventually...... you know, replace those calories, right? So what you... So, here's a hypothesis, right? To which I cannot, um, I cannot prove. But I think that, you know, when you, when you exercise, right, you're also going into negatogen- negative energy balance, 'cause you're burning energy. You're not eating while you exercise, at least most people aren't, right? And, and your, and your body's turn, you know, turning on all kinds of mechanisms to, to, um, to cope with that negative engin- energy balance, you're turning on all kinds of repair and maintenance mechanisms. When you, when you, when you're go through intermittent fasting, you're basically doing the same thing, but less acutely.

    12. SBSteven Bartlett1:07:23

        Mm-hmm.

    13. DLDaniel Lieberman1:07:24

        It's, it's a more gradual level. And I... And if you look at the, at the, at the genes that are turned on by exercise and the genes that are turned on by intermittent fasting, many of them are the very much the same. And I think it's because you're basically turning on genes that are responding to that negative energy balance. Um, but, um, but I would argue that you're gonna get more of a bang for your buck by exercising than just going through intermittent fasting.

    14. SBSteven Bartlett1:07:46

        Or both?

    15. DLDaniel Lieberman1:07:48

        Well-

    16. SBSteven Bartlett1:07:48

        Or is that a bit too much? (laughs)

    17. DLDaniel Lieberman1:07:49

        Yeah. I mean, intermittent fasting might be a kind of a easy way to get some of the benefits of exercise without exercising. It might be. (smacks lips) I mean, obviously, we went, we, you know... There's nothing necessarily wrong with intermittent fasting, but I'm not sure that it has some of the huge benefits that people claim. Now, keto diets are a little different, right? So keto diets are when you're, you're basically avoiding any carbohydrates. (smacks lips) And carbohydrates, the, the basic building block of most sugars is, is glucose, right?

    18. SBSteven Bartlett1:08:16

        Mm-hmm.

    19. DLDaniel Lieberman1:08:17

        Glucose is the sort of si- a simple form of sugar that are basically in starches. There, there's some other sugars. Fructose is also, which is the kind of the sweet one. But when you basically stop taking in glucose, right, you're now basically taking in only fats and in, so instead of using glucose to fuel your brain and, and other cells in your body, you're now using what's called ketone bodies. These are, these are... Since you remember we talked about how you when you break those fats down into small little units, those are ketone bodies, uh, they, um, they can be used as energy, but, um, they're more of a, it's kind of a backup energy source for our bodies than, than the primary energy source. So we, we use them, um, we tend, our bodies tend to use them when we don't have glucose available to us.

    20. SBSteven Bartlett1:09:02

        And does that mean the same sort of re- repair and restore mechanism kicks in, potentially?

    21. DLDaniel Lieberman1:09:06

        No, I don't think so.

    22. SBSteven Bartlett1:09:07

        No?

    23. DLDaniel Lieberman1:09:07

        Because that's not negative energy balance. You're just using an alternative fuel in this particular point.

    24. SBSteven Bartlett1:09:11

        'Cause a lot of doctors have sort of prescribed the keto diet for people that have like epileptic seizures.

    25. DLDaniel Lieberman1:09:16

        Right. And I don't think anybody knows, I'm not a neurologist. (laughs)

    26. SBSteven Bartlett1:09:19

        Yeah.

    27. DLDaniel Lieberman1:09:19

        But I don't think anybody knows why ket- ke- uh, ke- high-ketone diets are so, uh, beneficial for epilepsy. But it could be that they do and I just don't know and I'm, that's, that's not my, it's not my subject. But anyway there's a, there's a, there's a thought that if you just, you know, essentially keep your insulin levels low and rely on ketone bodies instead of glucose, you can, you know, do all kinds of miraculous things. Um, for weight loss, if you look at the data, yes it does tend to sh- uh, lead to rapid short term weight loss. But the data don't sug- don't show it is very effective as a long term weight loss strategy and I think your, your example, your own anecdotal account is, is sort of typical.

19. 1:09:59 – 1:15:14

    Are we too comfortable as a society?

    1. DLDaniel Lieberman1:09:59

    2. SBSteven Bartlett1:09:59

       Are we too coddled? Are we coddling our kids too much and coddling ourselves too much and is that causing some of these mismatch diseases?

    3. DLDaniel Lieberman1:10:08

       Well, I'm not a psychiatrist or a psychologist (laughs) so, uh, I-

    4. SBSteven Bartlett1:10:12

       Physically coddled.

    5. DLDaniel Lieberman1:10:13

       Oh, physically coddled. Um-

    6. SBSteven Bartlett1:10:15

       You know, stopping kids from doing anything that might hurt them or, you know, the risk-

    7. DLDaniel Lieberman1:10:19

       Yeah.

    8. SBSteven Bartlett1:10:19

       ... aversion and...

    9. DLDaniel Lieberman1:10:20

       Yeah, I think so. Yeah. I mean-

    10. SBSteven Bartlett1:10:21

        The comfort industry?

    11. DLDaniel Lieberman1:10:23

        Absolutely. I mean, you know, I have a whole chapter in my book on comfort, right? We have this idea that comfort is somehow good for you, like where does that come from, right? Um, comfort is nice but, you know, I mean who wouldn't rather be in business class than in economy, right? But, um, but, uh, is a comfortable shoe better for you, right? Is like, is sitting in chair better for you than walking around or standing? Is it better to take the stairs or take the lift or the elevator? Um, so comfort isn't necessarily good for us, but when we, but we now live in a world where we're able to have incredible levels of comfort and, um, and it's definitely not doing us some good because, you know, kids need to run around. I mean, every kid needs a good hour of physical activity a day to build a healthy skeletal system and to, you know, for, for all the other benefits that come from physical activity. So preventing our kids from running around and doing physical activity is definitely a, a problem.

    12. SBSteven Bartlett1:11:09

        Is there any evidence that our kids are getting sort of physically weaker or physically-

    13. DLDaniel Lieberman1:11:13

        Oh, absolutely. Absolutely. I mean, we have data in the United States. I mean, they used... We have this thing called the Presidential Fitness Test, right, that was started I think maybe it was Kennedy who started, I can't... Some president a long time ago started it. So we have decades worth of data and kids today are, are, are less fit, absolutely. Uh, any, ask any army recruiter, they'll tell you that fewer and fewer army recruits are, are physically fit and able to be-

    14. SBSteven Bartlett1:11:35

        What about s- w- strong in terms of bones and our skeletal structures?

    15. DLDaniel Lieberman1:11:39

        Yeah. Our, our, I mean, the rates of osteoporosis are going up and, and one of the reasons for that is that, you know, loading our skeleton when we're growing up causes the skeleton to, to accrue mass, to, to grow bone. If you don't, if you don't exercise, right, and especially weight-bearing forms of exercise, you don't grow as much skeleton and then when you hit, you know, normally people stop adding bone around 25 to 30, right? So I don't know how old you are, but you-

    16. SBSteven Bartlett1:12:04

        31.

    17. DLDaniel Lieberman1:12:05

        All right, so you're, that's it.

    18. SBSteven Bartlett1:12:06

        (laughs)

    19. DLDaniel Lieberman1:12:06

        You have no more bone to add and the rest, for the rest of your life you're gonna start losing bone, right?

    20. SBSteven Bartlett1:12:11

        Oh, sugar.

    21. DLDaniel Lieberman1:12:11

        But fortunately, you look like a reasonably fit person who is very physically active, so you probably built up enough bone. So having a, a high level of bone when you're in your 25, when you're 25 to 30, as you lose bone, that's gonna protect you from falling below that threshold that's gonna give you osteoporosis.

    22. SBSteven Bartlett1:12:27

        Mm-hmm.

    23. DLDaniel Lieberman1:12:27

        But if you aren't physically active when you're young, you have less bone to start with, you're still losing, you're just gonna lose bone, and you're gonna be much more likely to fall below that threshold, you're much more likely to get osteoporosis, and rates of osteoporosis are rising. Again, it's another one of these mismatch diseases that's rising radically throughout the world. Exercise also helps prevent, uh, bone loss because it, it, it suppresses the cells that, that essentially cause our bones to start being resorbed. So, so it's a, it's kind of a double whammy, you know, not, don't, not enough exercise when you're young, you have less peak bone mass, not enough exercise when you stay old, your bones are gonna lose mass at a more rapid rate.

    24. SBSteven Bartlett1:13:03

        I was reading in your book that, um-... teen tennis players can become 40% thicker and stronger when they become older because they were using-

    25. DLDaniel Lieberman1:13:12

        In the, in the arm that they use, yeah. So-

    26. SBSteven Bartlett1:13:14

        Oh.

    27. DLDaniel Lieberman1:13:14

        So when you play tennis, right, the arm that you use, which is whacking the ball, that's getting more loading than the arm that you simply use to throw the ball in the air.

    28. SBSteven Bartlett1:13:21

        Oh.

    29. DLDaniel Lieberman1:13:21

        So there's an asymmetry. So the humerus, the upper arm bone of tennis players, can be like 40% thicker in the arm that they use to whack a tennis racquet.

    30. SBSteven Bartlett1:13:28

        The bone?
20. 1:15:14 – 1:16:52

    Puberty has changed, and we’re going into it earlier than ever before.

    1. DLDaniel Lieberman1:15:14

Episode duration: 1:33:33