Your Body Was Built For a World That's Gone | Daniel Lieberman

I define mismatch conditions as problems that are more common or more severe because our bodies are inadequately or imperfectly adapted to the novel environments in which we live. The average big supermarket has 30,000 to 40,000 different products. More than half of those products, depending upon the supermarket, are what we call ultra-processed, right? They're loaded with sugar and fat, all kinds of additives. The fiber has been removed. They're junk food, right? And we are mismatched to those foods, but those foods are also hyper-matched to us. The manufacturers of these foods have figured out what turns on our brains. We don't have to know how to get our food. We now need to know how to choose our food. So Daniel Lieberman, it's a pleasure to meet you. Thank you. Pleasure to be here. Thank you for being here. So you are a professor of evolutionary biology at Harvard, and you have spent your career studying how we can look at evolution to understand the present, how we can look at the lens of physical activity, exercise, our physiology, and what we eat based on what we know from our evolutionary past. So given you spent your career on this, I know that you've probably been very sure this is the right way of looking at things, but can you just explain exactly why you think evolution is the framework to be looking at this, please? Well, I mean, simply put, there's a famous old phrase in our field that nothing in biology makes sense except in the light of evolution. And I think that applies to health and disease and illness and diet and physical activity, all those things. And the reason for that is that we weren't designed, we weren't engineered, we evolved. And if you want to understand why we are the way we are and why things are the way it works, and also to give ourselves some context, evolution is absolutely critical. So evolution alone doesn't answer these questions, but it's a part of the mix that we should be thinking about when we consider what should we eat, how should we be physically active, why is physical activity healthy, why are we prone to obesity? And you combine evolutionary information and evolutionary theory with biomedical information and social studies, data from anthropology and psychology and history and all that, you have a very rich appreciation of questions that are really important. So I know that in your work you look at contemporary hunter-gatherers, but you also look further back. For these massive questions of health, of physical activity, exercise, and also diet, how far back do you think we actually need to go? Well, I mean, you could go back to the beginnings of life, of course, but that might be a little bit extreme. I go back to the divergence of humans and chimpanzees, because that's really where we start off on this really kind of special trajectory. And we evolved from a creature that was something like a chimpanzee, and that evolutionary transition really started us off on some really important differences. For one, for example, is that most animals are pretty active, but as we were talking about earlier, chimpanzees are actually incredibly inactive. They're kind of one of the couch potatoes of the animal world, right? Typical chimpanzees spend about half as much physical energy and physical activity for their body size as other animals. So we evolved from very inactive creatures, and we also evolved from creatures who were basically frugivores, who ate mostly fruit, and then selection changed us. So knowing where we came from helps us understand how we were selected to be different, how we selected to become the very unusual creatures that we are, with big brains and long life histories and very odd diets and incredibly physical activity capabilities, like running marathons. That last common ancestor with chimpanzees helps anchor that and helps us understand that story. Our last common ancestor with chimpanzees, the date is a bit unclear. We haven't got data from that last common ancestor, unfortunately. We do have some very old fossils that we think are potentially on our lineage rather than on the chimpanzee lineage, contested. I've worked on some of them. So you know all too well that there's been a lot of change in those millions of years since that divergence. Could you just touch on some of those key changes, please? I know that we have the dawn of new genuses throughout that time, which brought about new, big adaptations. And you mentioned the big brain and everything like that, that we see as being with the emergence of our own genus, Homo. So would you mind just talking us through that? Okay, so seven million years of human evolution in one answer. But I'll do my best. So I would say there are five major transitions. So the first transition is the origins of the hominin lineage. And really, that was about becoming bipedal. So the very first creatures, like Sahelanthropus, or Auroran, or Ardipithecus, these earliest hominins, they're basically like chimpanzees in many ways, except we can see that they're bipeds of some sort. They're mostly eating fruit, but they're beginning to eat more things other than fruit. Chimpanzees mostly eat fruit, but they'll eat some other stuff. These hominins are living in more open habitats, so they're getting up, walking around, and they're eating less fruit. The next big shift were the Australopithecines, you know, like Lucy, right? That starts around four million years ago. And the Australopiths, and there are quite a lot of them, and they're very confusing, all the diversity of them. But they're basically better walkers, right? They're able to walk long distances quite efficiently. And they're also diggers, right? They start eating underground storage organs. So they're changing levels of physical activity, and they're also changing their diets. And an important thing about human evolution is that we never lost any component of our diet. We just kept adding more and more things. So they're still eating fruit, but now they're digging underground to get underground storage organs, tubers, roots. And this is where plants store their energy. So these are very energy-rich foods, if you can get them, but you have to dig to get them. And then the next transition, which I think is the most important transition in human evolution, is the origins of the genus Homo. That's like Homo erectus, right? And this is the origins of hunting and gathering, right? And the hunting and gathering system, I think, is by far the most important transformation that occurred in our evolutionary history. We have a system where there's some meat-eating, so scavenging or hunting. You have, of course, gathering, but instead of just picking berries off roots, you're extractive gathering. You're getting high-quality resources. You have food processing and tool-making, right? So, I mean, that may start a little bit earlier, but in the hunting-gathering system, it's crucial, right? They're making stone tools. They're cutting up their meat. They're cooking. It didn't all happen at once. And then, of course, you have social shifts. You have cooperative breeding. You have cooperation and probably a much more intensive group kind of dynamic. And that goes on for millions of years. And then, really, of course, there's been transitions. They have more cooking. Brains get bigger. We get more body fat. And then, finally, you get the origins of modern humans, sometime between about 200,000 and 300,000 years ago. And we're basically still very much like Homo erectus from the neck down, although you have some minor changes. What's different about us is that we have, well, we and also Neanderthals and other sort of late archaic humans, we have much bigger brains. And also, we have much smaller faces, especially even compared to Neanderthals. Your face is half the size of a Neanderthals face in terms of volume. But most importantly, we have cultural innovation. When you get modern humans, all of a sudden, you just get this explosion of innovation. And modern humans, of course, stay in Africa, but they also disperse out of Africa. And quickly, modern humans, by 60,000, 40,000 years ago, they're everywhere. They're all over the old world. They get across into the new world by 15,000 years ago. Maybe a little bit older. And you have hunter-gatherers all over the planet. So those are, to me, the big major transitions. But there's two more that are also really important, right, that happened much more recently. And the last two transitions, from the perspective of health, would be agriculture, which starts around 12,000 years ago in some parts of the world, much more recently in others. And of course, that is a big shift in what we eat. And instead of hunting and gathering, we're growing our food. And then most recently, just the last few generations, is the Industrial Revolution. And if anything has changed our lives the most, it's probably that, right? All of a sudden, we have machines replacing human labour. We have factory food. I mean, last night, I got in a metal tube and flew here to England. I mean, the transition that occurred because of the Industrial Revolution is extraordinary. Thank you, and you did incredibly well to synthesise those millions of years in such a short amount of time. So thank you for that. As I was listening to you there, I was just really struck by how much those transitions just really play into our physical activity, the transition to more open habitats, what that does for what we need to do in terms of our physical activity, how that changes what we eat, and then the repercussions of more recent transitions for health and disease today. But before we kind of go on to the today, just to keep on the past, just a little bit longer, what are the lines of evidence that we can look at to learn about things like what we're evolved for for our physical activity, our diet, and our health? Physical activity and diet, of course, you use slightly different data. For physical activity, some of the data comes from contemporary studies of hunter-gatherers. I mean, we have some idea of how much physical activity hunter-gatherers today have to engage in. And that, you know, we can use that information to help kind of understand at a bare minimum because what Homo erectus must have done. That's not direct evidence. It's indirect evidence. But even more importantly, we can look at the fossil record. I mean, I've spent a lot of time studying fossils from that time period, and we can see traces in the fossil record of, you know, literally from our heads to our toes of evidence for shifts in our locomotor adaptations. So for example, with the genus Homo, we lose the ability to become really good at climbing trees, which the australopiths were still pretty good tree climbers. We stayed good at walking, but we added running. And so I can see, for example, in the Turkana boy, a famous skeleton that's 1.6 million years old of a Homo erectus juvenile. He has the anatomy of a runner. He's got a really big gluteus maximus. We can tell he had a long Achilles tendon. His feet were eaten by a crocodile, but we have other feet which show that they have a proper arch in the foot, and the arch is really critical for running. It's not so important for walking. The vestibular system is better for balancing the head from the jiggling forces caused by running. They have a special adaptation, you know, for balancing the head so you can stabilize the gaze. They're called the nuchal ligament, something we've studied a lot in my lab. So we have literally a ton of evidence that we added endurance running, plus walking. Of course, there's a lot of walking. Walking is still the main form of physical activity. And that's how we hunted, because think about how you hunt if you can't run. It's kind of a problem, especially in an era before the projectile technologies, because these early hominins, early Homo, they were hunting before the bow and arrow was invented. In fact, putting a sharp pointed stone, a spearhead, that wasn't invented until at least 500,000 years ago, maybe even younger. So they were basically hunting animals with nothing better than sticks and stones, basically. And so they did something called persistence hunting, where you can run animals down. And that, of course, ties into our diet, right? Because we know that meat became a very important component of the diet. They were still eating tubers and underground storage organs, just like hunter-gatherers do today. But we don't know exactly how much meat they're eating. It's impossible to guess. We have also isotopic evidence. We can look at their bones and teeth and look at the chemical signatures of their diet. We can look at the scratch marks on the teeth, get more information from that. We can look at archaeological sites and find the preserved bones with the cut marks on them. So we have some idea that they're eating a very diverse diet that included some proportion of hunted meat. Probably a majority of their diet came from plants. And they're processing, so we can see that they're making stone tools. There's a big debate about when fire started. My colleague and friend Richard Wrangham thinks it's two million years old. The oldest archaeological evidence that's really clear is maybe a million years old. But certainly by 400,000 or 500,000 years ago, cooking was rampant. Everybody was cooking everything, basically. And of course, that's important because once you start cooking your food, you get way more energy from your food. So that was very important. So gosh, there's so many lines of evidence. It's really a challenge to put them all together, but it's also a lot of fun. So I know that for your work, you do a lot of anthropological work with contemporary hunter-gatherer populations, which maybe give a little bit of an insight into perhaps more of the behavioural components that you may not be able to do from the cut marks on teeth and the stone tools that we have left behind and the isotopes that we know that maybe they had a bit more of this type of food than others. Which hunter-gatherer population are you particularly involved in researching in? And what can that tell us about our physical activity, what we're adapted for, and also our diets? Well, actually, I've observed hunter-gatherers, but I've actually not collected data on hunter-gatherers. I'm like everybody else. I read the literature that my students and colleagues have produced. Almost all the fieldwork I've done has been with farmers, with subsistence farmers, looking at just how physically active people were before agriculture. But I've certainly pored through the ethnographic literature on hunter-gatherers. And we have some data and part of the problem is that hunter-gatherers today are, well, they're contemporary. And none of them are completely isolated from the modern world. I mean, I've gone to visit the Hadza, which are a group in Tanzania. And they have cell phones and they send their kids to school on Monday and they come back on Friday. And they're very used to people like me who arrive in land rovers and want to spend time with them. The anthropologists have become part of the industry for them. It's not like getting in a time machine and going back a million years. But it does give you some sense of the challenges and the way of life of people before farming, right? You get up in the morning every day and there's usually no food at camp. And every day people go out and they hunt and gather. And I've gone out with women as they dig tubers and I've gone out with the men as they've gone hunting and collecting honey. And you sort of get a sense of just how that it's very physically demanding. Some people would think it's super physically demanding, but it's not crazy physical demanding. It's just a lot more than what most Westerners do. So the average hunter-gatherer spends about two and a quarter hours a day in what's called moderate to vigorous physical activity. So getting their heart rate up to like a brisk walk, you know, a brisk walk, getting your heart rate up to about 50% of its maximum. But they spend a lot of the day doing what you and I are doing now, sitting, right? Except when they're sitting, they're very active. There's always like babies running around and they have to get up and tend the fire, et cetera. They don't sit for long periods of time. They're constantly getting up, but there's always a lot of chaos. They don't sleep that much. And I think the other thing I've learned spending time with them is that they don't, they'll eat anything. You know, we have this idea that there's like a hunter-gatherer diet and like there's a paleo diet and there is no paleo diet. If it moves and it's edible, they'll eat it. And if it grows and it's edible, they'll eat it and they'll find some way to consume it. And in fact, we did a study of all the really good data on hunter-gatherer populations in the tropics. Because we're interested in how those diets compared to the paleo diet. Which tells us, you know, what we're supposed to eat. And they run the gamut, right? There are some populations that basically eat huge amounts of animal food. And there are some populations for which there are almost no animal food and everything in between. We evolved to eat absolutely everything. And because what hunter-gatherers care about is they're not trying to, you know, find just the right diet for their heart so they can live to be 80 or 90 and avoid osteoporosis and Alzheimer's. They're trying to get enough food so that they can survive and have as many children as possible. Just like every other animal. And so we evolved. So I think one of the things I've learned by spending time with these populations is just how much of the day and how much time is spent getting food, right? That's job number one is how to get food. Whereas, you know, in my life, when I want food, I just, you know, I go to a supermarket and there's 30,000, 40,000 different kinds of food there. I mean, I don't have to know anything to get my food. And for them, that's their job. Knowing how to get food is the number one thing you have to learn in order to be a hunter-gatherer. And you actually touched there on kind of this mismatch between the way that we evolved to have to hunt and gather for our food and the fact that that's just no longer the case for so many people today. And so there's a clear sort of evolutionary mismatch there. Could you just explain a little bit about what that mismatch is, please? I define mismatch conditions as these are problems that are more common or more severe because our bodies are inadequately or imperfectly adapted to the novel environments in which we live, right? An obvious example would be sugar, right? We evolved to love sugar. I mean, the number one food that Hadza like is honey. I've seen Hadza eat more honey than I can imagine possibly eating. But they don't get to do it very often. But now we pay extra money for foods that have less sugar in them, right? It's crazy, right? We have such an abundance of sugar available to us and too much sugar causes a multitude of problems, right? So we're mismatched to that. But there are so many levels of this mismatch. Sometimes they're hard to figure out. I mean, some are obvious. Sugar is one of them. But others are less obvious, like shoes, for example. Some shoes are better for you than others. And I could go on. So people like to often evoke mismatch. But it's a hypothesis that we need to test. Would you mind just explaining a bit more detail what those mismatches may be then? So shoes, for example. Sure. Well, I think there are three major categories of mismatch. So one kind of mismatch is mismatches of too much of a stimulus, right? So too much calories, too much sugar, too much fat. These cause obesity. These cause type 2 diabetes. These cause, gosh, you know, all kinds of other cardiometabolic diseases. Another mismatch might be a mismatches of too little. So not enough fiber, for example, can cause the least, probably the least, worst of them is constipation. There are all kinds of other problems caused by not getting enough fiber. It increases your risk of cancer and on and on and on. Another mismatch of too little might be too little sleep or too little physical activity. That's an obvious mismatch, right? And then finally, mismatches of novelty, right? Simplest example would be tobacco. Obviously, you know, tobacco is a poison, right? It's a toxin that we breathe in and makes some people happy. But there are plenty of other sort of novel things which can cause damage, toxins, too much chairs, you could argue about it. I mean, we could go on, right? Our world is full of these mismatches. When did those mismatches really start then? So I know you've already kindly talked through the major transitions of human evolution in just a few minutes, and you talked about two very recent ones that have created seemingly just such a massive shift from the really long period of evolution that came before. So could you just explain exactly kind of when these started? Natural selection actually works through mismatches, right? Imagine you're, I don't know, think about the famous story of giraffes out in the savannah, right? And if the trees are really high and your neck is short, you're mismatched to those trees, right? So there's gonna be selection for giraffes who have slightly longer necks, right? So most natural selection is caused by some form of mismatch. But these are, again, they're conditions in which you are not really adapted to the environment you're in, and that ends up leading to selection. But cultural evolution, right? The changes that we have created in our world through culture have accelerated the environmental changes to such an extraordinary extent that the mismatches that we now confront are mostly the result, to some extent, of the agricultural revolution, but really it's the industrial revolution. It's not until the industrial revolution that people could afford not to be physically active. It's not until the industrial revolution that people could have a lot of sugar. I mean, sugar was the first industrial product, right? With the slave trade and the first sort of real machines to refine the sugar. And then came rolling mills to give us white flour. So the industrial revolution has transformed our world so rapidly that most of the chronic diseases that we get today were rare before the industrial revolution. I mean, sure, some people had diabetes before, but diabetes really shot up during the industrial revolution. And places where, like I do field work in Rwanda and Kenya now, they're the diseases that are rising at the fastest rate in those countries as people, their metabolism is changing because of access to sugar and fat and all these high-calorie foods. And also, they're becoming less physically active. These transitions occurred in a blink of an eye. We're talking just a few generations. And there's no way for natural selection to catch up, right? In my lifetime, in my lifetime since I was born, the percentage of Americans with obesity has quadrupled in my lifetime. That's not because of genetic change. That's because of environmental change. It's because of our food and to some extent, our physical activity. You mentioned food there, and we hilariously had to walk through a wall of a lot of processed foods just outside to get into this room. There was so many different flavors and additives, I'm sure, just on that table alone. And it's really clear that the food landscape has really changed for a lot of people today. And the thing that you mention a lot in your book that you have out, fed up, is the fact that we actually now are able to kind of eat for pleasure. We're able to choose what we eat and we can then find it very hard to lose weight if that's something that we choose to do. So can you just talk to me about sort of the changing role of food in our lives, please? Oh, gosh. You got a few hours? I mean, look, but you mentioned, I think, maybe the most important one. Remember, we were talking about hunter-gatherers earlier. Hunter-gatherers needed to do a lot to get their food, right? But they didn't. But no hunter-gatherer woke up in the morning and said, you know, I think today I'm going to have kudu with a side of, I don't know, this particular kind of tuber. They go out and if they happen to get a kudu, that's what they'll eat. And if they happen to get those tubers, that's what they'll eat, right? There are no menus, right? Today, you walk into a supermarket, we don't have to know how to get our food. We now need to know how to choose our food because we're confronted, the average supermarket, you know, big supermarket, has 30,000 to 40,000 different products. I mean, that's a staggering amount. And a large percentage, more than half of those products, depending upon the supermarket, are factory manufactured to be what we call ultra-processed, right? They're loaded with sugar and fat. They're loaded with all kinds of additives. The fiber has been removed. They're junk food, right? And they're full of additives, emulsifiers, stabilizers, you know, colorants, flavorings, God knows what's in these foods. Many of these additives, we have no clue what they do to us. And the combination of the energy density, the additives, the sugar, the absence of fiber, the added saturated fat, all of these things together, plus the fact that they're manufactured to be enticing, convenient, affordable, you know, long-lasting, is clearly causing havoc, right? It is a major cause of the rise in obesity, and in cardiometabolic diseases, and all kinds of other, you know, inflammatory diseases. There's no question that we are, in a sense, we are mismatched to those foods. But, you know, those foods are also, as I call it, hyper-matched to us. The manufacturers of these foods have figured out what turns on our brains, right? An example is, if you take a food and you put a lot of fat in it, it's disgusting, right? It's greasy, it's whatever. And you take another food and you put way too much sugar in it, it's cloying. Put a lot of fat in, and a lot of sugar in it, the combination, they balance each other out, and they create what's called the bliss point, right? And our brains just light up. We just love this stuff, especially if you add a lot of salt, right? And we just can't stop eating this stuff, right? And these foods have been carefully designed, you know, with large focus groups to hit those bliss points, to get us to eat more and more and more of that stuff. And we all know the result. You don't need an MD or a professor to tell you that. So it sounds like then they've really been able to kind of harness the sort of adaptations that we have to maybe want to eat those foods, but then really, like, run away with it. Exactly. Can you think of a natural food that's high in fat and sugar? The one. Is there one? Yes, there's just one. Milk? Yes, it's milk. I'm proud of myself. Very well, you get high marks, right? Milk, which we, you know, I spend our first few years of life drinking from our mother, is the only natural food that's high in fat and sugar. And now, you know, fortunes are made by combining fat and sugar to make foods that we just love, right? I mean, I'm no exception. I put a piece of chocolate cake in front of me, I will eat it, right? I love donuts. I love all these things, right? I try not to eat too many of them, but we love these foods, and so now we've managed, we've created a world where we get what we want, but that's actually not, so in that way, they're hyper-matched to us, but we're also mismatched to them in the long term. And here's the thing, each little, you know, each donut, you know, that doesn't have much of an effect, but over time, donut after donut, cookie after cookie, Dorito pack after Dorito pack, whatever it is, Mars bars, slowly, slowly, slowly, the effects add up, and it takes a long, long, long time. And it's very hard for us to figure out the relationship between the food that we're eating and the consequences, which can happen 10, 20, 30, 40 years later on. So it's really fascinating then that we have this kind of mismatch and hyper-match, and the fact that then there's this kind of changing relationship to food that's happened very recently. And I know that in your book, you really talk about kind of the basic equation of life being food in equals babies out. Could you just explain that a little bit, please? Well, I mean, ultimately, that's what all animals are selected to do, to eat in order to reproduce. That's what a bacteria does. That's what a virus does. That's what chimpanzees do. And ultimately, from a selective perspective, that's what we evolved to do. We have culture, we have other desires and needs and goals than simply eating to have babies, but that's what we evolved to do, right? So that's the evolutionary legacy that we have to contend with. And so we have cravings for foods that are beneficial for reproduction, right? That's one of the reasons why humans are so vulnerable to these high-energy foods, right? And one of the things about humans is that we evolved to be unusually fat. So your average chimpanzee, which we were talking about chimpanzees earlier, has maybe about 5% body fat, and that's typical for most mammals. There's not a lot of body fat on most mammals. A thin hunter-gatherer female has like 20, 25% body fat, right? We evolved to have a lot of fat because fat played an incredibly important role in our evolutionary history. Fat enabled us to help us have these big brains that constantly need a lot of energy, especially when we're children, right? A baby is basically just a brain with a tiny little body attached, and 50% of its metabolism goes towards feeding its brain, and it needs all that body fat in order to make sure it constantly has the energy to feed the brain. And then as we get older, we actually get fatter, right, for a while. Then we get to go down. And fat is important for our reproductive strategy. Mothers need fat for nursing and so on. So if you're gonna go run a marathon or do the Great North Run or do a persistence hunt, you need some body fat to help you get there, especially if you hadn't had breakfast. So fat played an incredibly important role in our evolutionary history, which is one of the reasons we love it and we're so good at storing it. But here's the thing. We never evolved to lose it. There are no adaptations that humans have to naturally lose fat. In fact, we have the opposite. We have a whole suite of adaptations to hold onto it. So when people go on a diet, they now have to fight millions of years of adaptations, and there are many of them, all of which are geared towards keeping us to hold onto that fat, right? If you lose fat, you have a hormone called leptin. Those levels plunge, and that leptin plunging makes you hungry. When you lose fat, your stomach produces another hormone called ghrelin that makes you hungry. There are other hormones, PYY, CKK. There are all these neuroendocrine hormones whose job it is to keep us from losing body fat. So now we have this system where we have evolved to eat all these high-energy foods, but they were rare, and we had to be very physically active. Now we don't have to do anything to get those foods. We don't have to be physically active, and manufacturers have figured out how to give us exactly what we want. And so the result is that in the United States, 75% of Americans are overweight or obese, and I don't know quite what the percentages are in England, but I don't think it's too far off. And then when they diet, they struggle. They struggle. And of course, the only thing that's really now changed it is now these RGLP1s, which for the first time in medical and evolutionary history, we can turn off people's appetite because the hardest thing about dieting is hunger. It sounds like the odds are really stacked against us in kind of the modern world with all of those facets coming together to really mean that we're then potentially holding on to more fat than we previously were, and then we're kind of finding it very hard to lose that weight without the kind of intervention of these new drugs. That's right. But we've stacked the odds against ourselves, right? We've created this system, right? And I think we have agency. We can do something about it. So I noticed, for example, when I go to a grocery store here in the UK, some of the foods, not all of them, but some of them have like a little yellow label, red label, and a green label. And you could argue about whether they're appropriately labeled, but at least it's information that people can have without knowing a huge amount, that maybe this is not such a good food, maybe I shouldn't eat this, or maybe I should eat it very rarely. That's a start. We could do a lot more of that. We could do more regulation. There's more that we can do. But yes, to go back to what you said, we have to focus more on prevention, but also you can lose weight. It's just hard. And we have to help people lose weight. But one of the key things that, and I think one of the key messages from an evolutionary perspective is that if you're struggling to figure out what to eat, if you're struggling to exercise, if you're struggling to lose weight, it's not your fault, right? It's because of our evolutionary history. And understanding that evolutionary history, I think helps people give context, gives them information, helps make them not feel like they're shamed or they should be blamed. Nobody gets obese because they want to. And nobody who's trying to lose weight wants to fail, right? It's hard. And so I think that evolutionary information I think is empowering and important because there's too many people who feel really bad about themselves and that ends up working against their efforts. And it's interesting there because I think in another way, the evolutionary reasoning has also been something that's been kind of jumped upon to kind of sell different types of diet. And I know that we mentioned earlier paleo diets and you immediately said, well, there's so many different types. There are people all over the world and there have been for thousands and thousands of years. Could you just talk a little bit about why the paleo diet maybe isn't the be-all and end-all? Almost every diet. So for the book, my wife and I tried almost every diet known to humankind that's kind of related to the evolution and history of diets. So that was an interesting experiment. And we tried the paleo diet. And look, all of these diets have a grain of truth to them, right? And the paleo diet is kind of a high-protein diet that says if you eat like our ancestors ate, you're gonna be healthy. And this is what we call the naturalistic fallacy and it's sort of true, but it's not completely true, right? So one problem is, A, we talked earlier about this, that our ancestors didn't eat in order to be healthy. They ate to have a lot of babies, right? So really, the paleo diet is really a reproductive diet. Second, the paleo diet does ban junk food. You're not allowed to eat junk food. You shouldn't eat food with added sugar. You shouldn't eat food with a lot of saturated fat. That's all good, right? So that's generally healthy. My problem with the paleo diet is it completely bans all grains, nothing. No bread, no oats, no whole grain, no oatmeal, no nothing, right? And it completely bans all legumes. So no beans, no lentils, no chickpeas, no soy, no peanut butter, which by the way is my favorite food. And the argument for that is that our ancestors supposedly didn't eat these things. Well, that turns out not to be true. We have lots of evidence that paleothic hunter-gatherers ate grains and legumes. So that's just nonsense. And the other argument they make is that these foods are full of so-called anti-nutrients that bind to the minerals and vitamins in your food and will make you malnourished, which is obviously ridiculous because when you cook your food, you basically get rid of them or reduce them to harmless levels. Otherwise, vegetarians and people around the world would be walking around malnourished and they're clearly not malnourished. If anything, they're overnourished. So the paleo diet has some good points, but I think it's as a kind of a general, as a diet, I wouldn't consider it the best diet. The other diet in there that I know that you struggled with among the various that you did was the raw food diet. Struggle is a euphemism. And the fact that that's also something that it kind of draws on evolutionary reasoning, but then is actually just not true. There's that fallacy again because cooking was a really big part of our... Yeah, so the raw food diet started at the beginning of the Industrial Revolution, right? When people are beginning to get diabetes and all these other diseases and they thought, animals that we're feeding, and the cows in Switzerland, they're not getting diabetes. So if we only ate raw food, then we would never... Because the idea was that cooking destroys the nutrients in food. Well, it's not true. It's actually the reverse. Cooking actually gives you more energy from your food because it breaks down the cell walls or it liberates the energy and it reduces the cost of, the metabolic cost of digestion. And in fact, cooking played such an important role in our evolutionary history that we're now adapted to eating cooked food and we're maladapted to only eating raw food. So raw food is typically... These are not hunter-gatherers, right? These are people going to the fanciest supermarkets you can think of and they're getting high quality foods that have almost no fiber in them and they're rich in all kinds of... They've been domesticated to be really, really nutritious. And even then, they're struggling to get enough energy. A lot of women who are raw foodists don't have normal menstrual cycles, right? Because they don't have enough energy, right? And I have to tell you, I mean, the hard thing about the raw food diet was that, I mean, my wife and I were just always hungry. Even though we were constantly processing our food, cooking it, anything but cooking, chopping it and dicing it and pureeing it and whatever. And I just couldn't... I was just hungry constantly. I lost weight. I mean, it was only a few days. And eventually, my wife gave up after three days. One morning, I went down to breakfast and she looked unusually happy. And it's because she snuck out and got a bagel. And I lasted just one more day. I mean, I just gave up. It was not for me. And it's not for most people. If you really want to go on a crash diet to lose weight, go ahead, try raw foodism. But it's a challenge. And so it sounds like kind of now we've evolved to have the processing from cooking, for example, but then they're at the extreme end of processing where we have the oft-processed foods that we talked about earlier. And this kind of change in landscape that's happened through that kind of transition to how much we process our foods, maybe, and what we're adding to our foods. Yeah. And that's really the industrial revolution. Why haven't we adapted to these new foods yet? Because it's a blink of an eye. The roller mill, right, to separate... You know, it used to be that you'd go to a mill, you'd grind your flour in a millstone, you'd have brown flour, right? You'd have whole wheat flour. It was only in the mid-19th century that roller mills were invented that instead of grind your flour, now you rolled the flour so you can now separate the bran and the germ from the starchy bit. And it was only then that people could have white flour. Before that, only the super wealthy could have white flour. Same thing for brown rice versus white rice and so on. So these technologies are just a few generations old. And evolution doesn't work that fast, right? I mean, yeah, it takes hundreds, if not thousands of years for natural selection to work. And furthermore, the diseases that we get from these ultra-processed foods don't usually hit us until we're in our 60s or 70s. And by then, natural selection doesn't really care about us. We're in what's called the selective shadow, right? We've had our children. We might even be grandparents at that point. And it's not like I'm going out and digging tubers for my grandchildren, right? I'm simply using up the money that they might otherwise inherit, right? So we're not contributing to their fitness anymore in the same way that grandparents did in the Paleolithic. And so there's not gonna be a selection against people getting diabetes and heart disease and cancers in their 60s and 70s. It's not gonna happen. We have to solve this problem without the help of natural selection. It's interesting because we do have examples of a change in diet leading to changing biology. So I think a key example being the lactase persistence changing as we had the domestication of cattle and then we go harking back to milk that we discussed earlier. But that took thousands of years. You know, between the first domestication of animals that could give us milk and the evolution of those lactase genes, was thousands of years. It didn't happen like that. It took a long time. So in between, you know what people did? They fermented their milk. They had yogurt and cheese and whatever or they farted a lot. So I understand what you're saying that we may have to wait thousands of years before we do start to see potential adaptations to the kind of new landscape that we're in and who knows what landscape it will be when it gets to that point. But you also, I know, talk about in your book variation between individuals and the fact that some people can seemingly eat as much ultra processed food they like and have no obvious negative repercussions for their health. Could you just talk a little bit about that variation, please? Well, we don't understand the variation. But yeah, for example, there's one, there's two different kinds of phenotypes in saturated fat. There are some people who, when they eat saturated fat, a lot of saturated fat, they end up with a lot of cholesterol molecules that are damaging and cause plaque hardening of the arteries. And there are others who produce fewer of those kinds of molecules. And we don't still yet know all the genes behind all that. So there is a lot of genetic variation that can affect the foods that we eat. But you're not gonna know who you are and what your genetic variation until it's too late, right? I think, and furthermore, your genes might protect you from one thing, but they're not gonna protect you from everything else. And the evidence is so clear. People who eat more ultraprocessed food are more at risk of, I mean, the list of diseases is so long, it would take us another hour, right? I mean, this is not a scientifically debatable issue. I mean, there is debate over exactly what it is about ultraprocessed foods that's causing all these problems. But there is no debate that the growth and the prevalence of these foods is causing widespread havoc, right? And so I don't think anybody should think, I'm genetically protected from this stuff, I can eat as much as I want. So you talked about the fact that you had a lot of different diets as part of writing this book, some lasting longer than others. What should we be eating? You know, first of all, there is no optimal diet, right? Because there is variation. Also, diet's not just about health, right? It's about things you love. It's about family. It's about culture. It's about tradition. But in general, if you stand back from all the various diets the ones that have the most scientific evidence are the ones like the Mediterranean diet that aren't really diets, right? They're basically traditional farming cuisines that don't rely on a lot of processing, don't have a lot of saturated fat, don't have a lot of added sugar, have plenty of fiber, have diverse nutrients, so you're eating a lot of plants, not too much animal food. And there are lots of these diets. Mediterranean is the best studied, but I think a traditional Asian diet would qualify, traditional Mesoamerican diet, traditional African diet. These diets, you know, cultures around the world evolved these diets for, you know, through trial and error for a good reason. They're nutritious. They're wholesome. Folks in these parts of the world had, of course, their health problems, but their health problems tended not to be a result of diet. Their health problems tended to be a result of infectious disease and, you know, high population densities and sanitation and so on. Now, where we've, you know, with vaccines and clean water, we've, you know, defeated a lot of those, but now we're being killed by our diet. If I were to go from the evidence, you know, and I like science, right? If I were for the best scientifically studied diet for which there are long-term, prospective, randomized control studies with mechanistic data behind them, you can't go wrong with something like a Mediterranean diet. Plus, it's kind of tasty. You mentioned earlier that there are some things that we can be doing to kind of nudge us in the right direction for people who aren't aware, maybe, of the health repercussions of particular foods that they're eating. You talked about the kind of traffic life system that we have here in the UK of the red, amber, and green for how much salt, maybe, in some food, for example. What are the things that can be done for the people who haven't got the luxury of being able to choose, maybe, a slightly healthier food because it's more expensive? What can we do as a society that that cultural stuff that you were mentioning earlier to help with this massive evolutionary mismatch that we've been talking about? If I knew the answer, I would tell you. I mean, this is a political problem. It's a social problem. It's also an educational problem. I think we don't— I mean, like, when I learned chemistry in school, right, we learned all kinds of fun stuff. But why didn't they teach us about carbon and hydrogen bonds in the context of, say, saturated versus unsaturated fats? Now we treat this as, like, abstruse knowledge, but it's not that complicated. We just don't teach that. We don't even teach medical students this knowledge, right? It's not in part of most medical curricula because doctors are there to treat us once we're sick, not to prevent us from getting sick in the first place, for the most part. So I think our educational system is one way. Another, of course, is that we— is how we tax and regulate foods, right? I mean, we could do a lot more to regulate foods. I mean, when you buy a packet of cigarettes, there's got these scary warnings on it, right? I mean, skull and crossbones, you know, this will kill you, right? Well, why don't we do that on junk food, right? I mean, the difference is that the junk food might kill you a little bit more slowly, and the dose is different. But, you know, cigarettes take a long time to kill you. Junk food takes a long time to kill you. This is not a scientifically debatable issue. It's a politically debatable issue. And so I think, you know, I think ultimately it's voters, politicians, journalists. We all have to get together and decide if we want to continue to have a system where our food gets us sick, and then we pay a lot of money and go through a lot of misery to treat the illnesses caused by our diet. I think pretty much everybody knows what a basic healthy diet is, but sometimes they can't afford it, or the food, it's, you're stressed, you come home from work, you've got, you have a long commute, you have lots of kids, et cetera, et cetera. You don't have time, and it's more expensive to cook the healthy food. Well, we can change that. I mean, there can be processed food that's healthy. They don't have to remove all the fiber. They don't have to add all that sugar and salt. They can make healthier processed food. We just have to demand it. Daniel, we have covered so much. You've covered the whole of human evolution. We've covered the massive changes of the past few millennia, and even just the past few hundred years, how that's impacting our health, what foods may be the best ones for us to do to eat, and even kind of what we could be doing to try and improve these outcomes. Thank you so much for your time. It's my pleasure. Thank you. If you enjoyed that fascinating discussion, then you're going to absolutely love our next video, which is all about the ancient humans we used to share this planet with and how their DNA is still within us today.