Herman Pontzer: what people get wrong about metabolism
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The Economist. This week, we'll be talking about the human body. In particular, how the body uses energy. I'm going to be speaking with a researcher who I've been fascinated by for a very long time. To explain why, I'll need to take you back to my childhood.

Now, I was a pretty healthy but also pretty chubby kid. And for as long as I've had control over what I eat, I'm talking about after leaving home here, I've been hyper aware of ways to keep my weight and various edible temptations at bay. So I followed various fad diets over time, including at one point the original low-carb Atkins diet.

And I've also spent a lot of time in gyms, on exercise bikes, cross trainers. I even tried out a spin class once and ended up vomiting straight afterwards. Never doing that again. Sometimes these diet and fitness regimes worked, but mostly they didn't because they were so hard to stick to. I did plough on though because through years as a science and health writer and speaking to many, many scientists,

I had learned that to stay healthy involved watching what you eat and also making sure to move around a lot more. That was the science that had been ingrained into me. The only thing that mattered if you wanted to maintain a healthy weight was calories in versus calories out. Aerobic exercise, running, cycling, swimming, these were the best ways to increase the second half of that equation.

Then I came across Herman Ponser's work and it kind of blew my knowledge of human metabolism apart. His research is all about understanding how and why human bodies use energy in the way that they do. He'd spent several years living with and studying the Hadza people, a hunter-gatherer community in Tanzania, and through them he discovered something remarkable.

To our shock, it was really indistinguishable the number of calories being burned if you're a Hadza man or woman versus your typical office worker here in the U.S. Who doesn't get 10,000 steps or 12,000 steps a day at all. Yeah, I mean, the typical American, I think, gets less than 5,000 steps a day or something like that. So a Hadza adult gets as much activity in a day as most Americans get in a week.

The jaw-dropping implication was that people who exercise more don't necessarily burn more calories overall. All that running, jumping and swimming I'd been doing for all those years had been pretty much irrelevant in my attempts to stay at a healthy weight. Herman wrote about all of this in a book that came out a few years ago, Burn.

His latest book, Adaptable, tries to make sense of those findings and takes the provocative ideas about metabolism plus many others and puts them into the broader context of how evolution has shaped human bodies. So as you can no doubt tell, I was really looking forward to sitting down with Herman to explore his ideas about metabolism and also why we have so many misunderstandings about it ingrained into the ways that we live our lives.

I'm Alok Jha and this is Babbage from The Economist. Today, Herman Poncer's guide to the human body. Herman Poncer, thank you so much for joining me. Thanks for having me. Herman, let's start with your hypothesis that people who exercise a lot don't necessarily burn more calories overall. It's the idea that energy expenditure is much more constant between people who exercise a lot and people who don't.

When you published this work, how did people respond? I mean, because it went against so much of the orthodoxy of what people think about weight management and exercise. Yeah, I mean, I think that there were sort of different camps had different perspectives on it. Most surprising thing, I think, was when I talked to other people who had spent their lives studying metabolism, like I was starting to do then. They said, oh, yeah, we see that sometimes. Yeah, of course. You know, energy expenditure is kind of the same across lifestyles. I thought, what? That's not what I ever learned about this stuff.

And of course, people who are very pro-exercise or, of course, the general public, I think, were really surprised by it, right? Because, of course, that's not what we're told at all. So it was a real eye-opener for me, and I think it was for a lot of people as well. A lot of pushback, of course. People are always hesitant with new ideas, I think. But over time, I think people have kind of come around to the general idea. Yeah. I mean, it's been more than a decade, and you've obviously gathered more evidence. It's

But let's go back to where that initial piece of work came from before we talk about its implications. The sort of groundbreaking research was based on your time living among the Hadza people in Tanzania. Can you just paint us a picture of their lives and how you ended up working with them?

Sure. So I should probably start by saying I'm an evolutionary anthropologist. So I'm very interested in how the human body evolved and how that evolutionary past kind of shapes the way our bodies work today. And I've always been interested in metabolism and energy expenditure because it's really where the rubber hits the road in terms of any species, ecology, it's evolution, right? Life is a game of taking energy from your environment.

and turning it into offspring. That's the game of life. That's fundamentally it, isn't it? That's it, yeah. And so, you know, we had, as I kind of got into this area of metabolism research, one obvious point of comparison that I really wanted was, well, how does our metabolism look

in a context that's much more like the ways in which our species evolved. So no culture today is sort of trapped in the past and is sort of a time machine to the past. But if you look at a hunting and gathering community today, well, humans were hunting and gathering for 2 million years before we were even homo sapiens. And so cultures that still have that hunting and gathering lifestyle are sort of a point of reference for understanding what that does to our bodies. And so there weren't any data on

on energy expenditures, metabolism, in any hunting and gathering communities. I thought, well, we have to understand what that's like. And going into it, I thought, well, they're much more physically active. I knew that. So they'll be burning lots more calories. That's what I wanted to check. Yeah, that was the base assumption, that these people, because they're literally hunting and gathering still, they're moving around a lot, they're going to be consuming and expending lots of calories.

That's right. So the Hadza are classic hunter-gatherers. Men hunt wild game. Women gather wild plant foods all day. No vehicles or guns or electricity or anything like that. They live in grasshouses in the middle of the savanna in northern Tanzania. Men get like 19,000 steps a day. Women get 13,000 steps a day and often, you know, with a kid on their back. So it's a really intensively physically active lifestyle. And that's where we wanted to go to understand what that kind of lifestyle does to our physiology.

So talk to me about the experiments you did. How did you measure the amount of energy being used by the people you followed? So we used this really fantastic technique. It's called doubly labeled water. And we use isotopes, special forms of water. You drink it. And then over time, we can watch your body flush out the hydrogens and oxygens. And it turns out that the rate at which you flush out the H's and the O's allows us to measure how much carbon dioxide your body makes every day.

And that's a very precise, accurate measure of how many calories you burn. Because CO2 is your waste product of metabolism. So we were the first to use this sort of state-of-the-art technique to measure energy expenditures in a hunting and gathering community. And your starting hypothesis, as you've said, is that you assume that these people would be burning a lot more calories. And what did you find? Yeah, well, to our shock, when we got the data and we're looking at it and comparing men and women from the Hadza community to folks in the US, Europe, other places, we

There was no difference at all. It was really indistinguishable, the number of calories being burned if you're a Hadza man or woman versus your typical office worker here in the US. Who doesn't get 10,000 steps or 12,000 steps a day at all. Yeah. I mean, the typical American, I think, gets less than 5,000 steps a day or something like that. So a Hadza adult gets as much activity in a day as most Americans get in a week. Right. So it's a real stark difference.

So the amount of calories burned was indistinguishable, despite there being such a huge difference in physical activity. I mean, when you get a result like that, you've got to check it, right? To make sure you've not done something wrong. And when it comes back again with exactly the same result...

what do you start thinking? I mean, what might explain this? That even though these guys are walking around so much, they're not actually expending any more energy. Because we've been taught to believe that the more energy you use, I mean, that'll have an impact on your metabolism, right? Yeah, exactly. So the first thing we assumed is that we got it wrong. So we double checked and used different methods to kind of make sure that we had a really strong result. And we did.

I should say we've replicated this in other communities now. We've seen this in other contexts. So it's not just the Hadza. And so what's going on? Well, that's been the focus of my research the last decade or so is trying to understand how the body's balancing the books because there's no magic here, right? If you're spending those calories on movement, and they are, they're not particularly efficient walkers or anything like that. They're not saving energy when they walk. If you're spending that energy on activity, like we know they are,

but the total calories per day is the same, well, then you must be saving energy elsewhere in what your body's doing all day. And this brings up the larger question of what is our metabolism doing? And the answer is, well, you've got 37 trillion cells at work all day throughout the day doing all kinds of things from your immune system to your nervous system to all of it. And so even in a really active person, most of the calories you burn all day are spent on non-activity tasks, on all the background stuff.

that your body does. And so what we think, the hypothesis right now is that by saving energy on some of those background tasks, they actually create enough room in their budget to have this high activity cost every day without changing the total number of calories burned

over 24 hours. So it's just if I understand that correctly, then the idea is that, you know, if you're walking around a lot, as these kinds of people are all day long, you are burning the calories for walking around. But it's just that the rest of your bodily functions, the background basal metabolic rate activities, they are compensating somehow by reducing their activity. So the basic functions of life.

Yeah, that's exactly right. So we see some evidence for this in various ways. One of the best ways to look at this comparison, the most controlled experiments are in athletes versus non-athletes, really active people versus not. We have a lot more data from those kinds of studies on the physiology of what's going on. If you look at athletes, they've got lower levels of background inflammation. Well, what is that? Well, chronic inflammation is your immune system being too active, unnecessarily active.

And so we know that people who are physically active, who exercise a lot, their inflammation levels come down. Well, your immune system is saving energy then by having less inflammation.

Things like testosterone and estrogen levels, right, in men or women, those are moderated in people who exercise more. And so, you know, really sedentary people actually have much higher levels of testosterone and estrogen than people who exercise regularly. And that's a good thing, by the way, because it's probably one of the reasons that exercise is so good and protective against reproductive cancers, for example. You don't have this hormone sort of, you know, promoting cell activity all the time that you don't need. And stress, we know. So if people who are exercising regularly...

their response to psychosocial stress is muted and kind of returns to baseline faster than people who are sedentary and aren't active. So there's all these different ways that the body is saving energy when you're physically active, and we think that's how the books are getting balanced. Hey, I want to point out that this is still an area that we're actively researching. I don't think we have all the answers yet, but that's what it looks like is happening.

What's nice about that is it also connects exercise to health in a way that I think we intuitively know is there, but gives us a mechanism for why. So why is exercise so good for us? And just to be clear, it really is.

Well, it's probably good because of the way it helps us rejuggle and change the way that we spend energy rather than just changing the total number of calories we burn. Yeah, I think it's worth just sort of pausing and underlining that fact, isn't it? I don't think that any of your work suggests that all those hours on the treadmill or walking are wasted in any way.

They're still doing all these useful things in the way you're talking about, which is to essentially take up your energy budget so that your body can't do worse things to you, basically. So exercise, you recommend exercise as a good thing, right? Absolutely, yeah. I'm just curious, can you do too much exercise? Some people get obsessed with this, don't they? Yeah, that's right. And so, you know, the way that your body is kind of re-juggling the way it spends its calories, shifting energy away from non-exercise tasks if you exercise more,

that eventually can lead to problems. So people who are really active, who have enormous exercise workloads, typically this is something we see with elite athletes, but anybody could be in this position. If you're spending so much energy on exercise that there's not enough energy left over,

for normal reproductive function, for example, or for your immune system because you've taken so much energy away from those other systems. You can get what's called overtraining syndrome. These days it's called REDS, relative energy deficiency in sports syndrome. It's all talking about the same thing, which is you don't have enough energy left in your body for all the sort of necessary functions. And people have issues like they don't recover from illnesses very well. Women often they'll stop cycling.

So you'll see these effects throughout the body if you go too far. But for most of us, that's not an issue. Something I kind of wonder about on all of that, we also hear about metabolism when it comes to people's changing metabolism as they grow. We hear that kids obviously have quite fast metabolisms for their size. And then is it a myth that in your midlife, your metabolism just drops and that's why people sort of pack on the pounds afterwards?

You've done some work to show that that's not quite true. Yeah, that's right. This really great technique that we use, this isotope tracking technique, there's a dozen or so labs that focus on this technique, have been pulling all their data together from studies over the past 20 or 30 years.

And so now we've got big data sets, thousands of people that we can look at, influences of size, age, lifestyle, et cetera, on energy expenditure. And so we had this really fun analysis that we published a couple years ago showing metabolic rate over the life course. So we had people in this study from eight days old up through people in their 90s. So we could really get a really good sense of how energy expenditure, your metabolism changes dramatically.

from birth till very late age. And, you know, there are a bunch of surprises there. The one being that from your sort of early 20s to late 50s, early 60s, your metabolic rate is just so stable, right? There's like no change at all. I'm in my 40s. I would not have predicted that. I feel different. And I think a lot of times when people feel different, maybe they put on some pounds, they blame their metabolism. I've been using it as an excuse.

Yeah, you know, I get that. I feel that same way. But, you know, sorry, it's not that simple. It's not just your metabolic rate slowing down. In fact, there's no evidence for that at all. What seems to be happening instead is people are probably eating more, maybe eating less healthy, maybe getting less sleep, those kinds of things that we know push people to eat a bit more as you get older. Yeah. Given your work in metabolism, you and your colleagues then, in understanding how

how our bodies use energy and the kind of constricted ability to sort of shift that, essentially. This idea that, you know, if I go off and do a 10K in the morning, I can have a huge pancake breakfast doesn't seem like a sensible idea from what you're saying, right? Even though, you know, in the sort of accounting way that we think about calories in, calories out, that makes sense. If we sort of ditch that,

What should people take away then from your research about how to maintain a healthy weight, given that they're doing exercise, given they're eating healthily? What's the sort of key takeaway? You know, I think that all of this points to diet and the foods we eat and the foods we put in our homes and surround ourselves with as the big lever. Much more so than exercise. Yeah, for trying to maintain a healthy weight or get to a healthy weight.

exercise is still really important. It can have some sort of knock-on benefits that are weight related, so it can help you keep your muscle mass up. If you're going to try to lose a lot of weight, exercise can help you keep the muscle on while you do that, so that's great. There's some good evidence that if you exercise after you've lost weight, it helps you keep it off, kind of helps regulate things in your body better, helps regulate your appetite. So there's lots of knock-on effects of exercise that can sort of around the edges help with weight loss as well, but really the big lever

Right. Is your diet. And is food then the explanation also for sort of modern ailments such as obesity rather than the explanations we've been hearing about much more, which is the people don't move so much. They're just sitting down all the time.

Well, it's both, right? You have obesity-related disease and you have sedentary inactivity-related disease. So if you want to keep your heart healthy, for example, heart disease is the number one killer worldwide. Well, obesity is a risk factor for heart disease, but so is sedentary lifestyle. So people who have a healthy weight but don't ever exercise are at risk of heart problems as well, especially as they age. And so exercise is important for so much.

But it just isn't going to help you with the weight side of things as much as diet is. Yeah. Do you think that your work in metabolism then is entering the sort of clinic and public health conversations as well? Because we still hear a lot about just maintain your calories, do more exercise. I mean, I've got an app on my phone, for example, that will tell me that I've done 500 calories worth of walking today so you can eat extra things. From what you're saying, that's nonsense.

Yeah. Your energy expenditure will fluctuate day to day. These kind of adjustments your body makes are kind of longer time horizon changes and sort of background stuff. And so if you exercise today and don't tomorrow, then yeah, you'll burn more calories today than you will tomorrow. But right, you can't sort of earn your donut by going on a run, that kind of thing. I do think it's beginning to enter the public consciousness, which has been really rewarding to see. Maybe we can sort of

know we've made it into the discussion more when places like the WHO, CDC, when their guidance on weight loss and on obesity clearly puts the emphasis on diet and talks about exercise as important, but less so in terms of the obesity aspect of things. What you still see all the time is, oh, it's either or, or it's both exercise and diet are both important. And the problem with that is

I think it lets people off the hook and it lets food companies off the hook and that kind of thing where we can say, well, I want to sell you a diet plan. Don't worry about exercise. Or, oh, I want to sell you an exercise plan. Don't worry about your diet. Or I'd like to sell you these foods. You can eat all these foods as long as you exercise. There's a lot of room for intentional misinterpretation there. And I think when we're clear about the message and about the science, it's a better public health message.

Herman, can I just step back a bit? You're an anthropologist, so the reason we talk about metabolism now is because of this research you've been doing for such a long time. But to put it into context in the sort of larger scheme of trying to understand how human bodies evolved...

Can I ask, metabolism, if it's so strictly stable in people, despite our attempts to fiddle with it every day, why has it evolved like that? The way I think we think about metabolism gets it a bit wrong. We often think about the energy needs that we have as this crucial requirement for calories, and it is that. You need to be able to have enough energy to fuel your body. But it isn't just a cost, right? Those calories spent aren't just a cost.

Those calories that your body spends, from its perspective, are investments. Those are calories invested in maintaining your body and keeping you healthy. Crucially, from an evolutionary perspective, those are calories invested in reproduction eventually, either directly or sort of long-term indirectly. And so an organism then, from that perspective, should be spending as many calories as it can every day without going bankrupt.

And so species metabolic rates, ours as well, are not just some bill that you get at the end of the day about how active you were, how big you are.

Those energy budgets are really calibrated strategies that every species evolves to sort of maximize and tune itself to its environment so that it's taking in as many calories as it can expect to get and spending those on useful things. So from that perspective, it makes sense that you would want to keep your budget as an organism stable over time, right? Not wildly fluctuating. And you want to keep that budget of calories as high as you can manage, right?

without putting yourself at risk of starvation. So every species' metabolism is an evolutionary strategy, and that's how I think about it as an evolutionary anthropologist. How does the human metabolism compare to our closest relatives? Are we particularly highly requiring of energy? Yeah, so our closest relatives in the tree of life are chimpanzees, bonobos, gorillas, orangutans. Compared to them, we burn a lot more energy every day, even after you control for body size and that kind of thing. And

That's crucial for fueling our big brains. Your brain burns 300 calories a day, every day. And that's equivalent to running a 5K, right? And that's just your brain. Our bodies in general burn more calories than the other apes do. So it's this strategy, there's this high energy ape strategy. That's us, right? And that's what we're evolved to do. We get away with it because we have this, on the other side of the coin, on the energy that comes in, we have this really great sharing strategy that no other ape has ever evolved. The hunting and gathering strategy

bringing energy in from different ways and sharing it, and that has allowed us to have this faster metabolism. Of course the metabolism that we have, there's this long and sort of winding evolutionary journey that's brought us here. And in misunderstanding our own metabolism until recently, there's a sort of theme that goes along with some of the ideas in your new book, Adaptable, which is all about how we actually don't know our bodies as well as we think we do. Even when you're studying as a doctor, as you talk about at the beginning of that book,

And I think it's worth sort of dwelling on some of those things that we don't understand about our own body. So we talked about metabolism and how it's much more different than we thought. And there's an evolutionary reason for that. But just from a purely visual level, I mean, tell me what's wrong with the diagram of the human body that we get in textbooks.

the one with the heart and the lungs and everything in perfect order that we kind of think is inside ourselves. - So, you know, part of my training in grad school, I took gross anatomy with the medical school when I was there at Harvard. - Were you intending to be a doctor or was it always an anthropologist? - Always an anthropologist. I was an interloper. I knew I wasn't gonna be an MD, but if I was gonna study the human body for my career, which is what I've been lucky to do, I wanted to really have a good understanding of it inside and out. So I thought it was a crucial bit of training to get.

So your job is to dissect an entire human cadaver. That must feel strange. It's very strange. It's a very surreal experience. But what you learn right away is that you've got the textbook in front of you, and it's got these diagrams detailed about how everything's supposed to look. As soon as you start doing your own dissection with your own

It's very clear that there's a lot of variation in there that isn't captured in the book and that this textbook human is a fiction. But, you know, we teach physiology to the average body, whatever that is supposed to mean. You're sort of told it works one particular way.

But that's not the truth at all, right? Our bodies are all unique, all diverse, and it's this interaction of environment and genetics. And that's, I think, the story I wanted to tell this new book is sort of how the body works and why it works so differently for each of us. Yeah. I mean, you describe how human bodies today can vary very wildly, especially in different places around the world. For example, human populations...

have established themselves in very high altitude environments where the oxygen in the air is poor. I mean, how have they managed to do that and what makes their bodies different to say somebody who lives at sea level? - That's a great question. So when we look across the globe, we see differences in how people look, all the obvious superficial differences, of course. We know that internally there's variation as well.

And a lot of that difference is just noise, right? It's just sort of genetic mutations and chance kind of bubbling up and creating this great cacophony of diversity. A lot of it is not an adaptation of anything in particular. The classic example is head shape. Anthropologists in the late 1800s were obsessed with head shapes. If you had a wide skull or a long skull, all these kinds of things.

Turns out, total noise. There's no why to any of that kind of thing. So a lot of features are like that. But in particular cases, like altitude, you have the right conditions to have real adaptation, a difference in the way our bodies work that is meaningful and actually fit to that environment.

And what you have to have is a really strong selection pressure, like the need to get oxygen. And it has to be stable over generations and specific to that location. If all those things are true, you get these local adaptations. People in the Andes, populations in the Himalaya, populations in the Ethiopian plateau are all sort of these independent populations.

natural experiments in how the body responds over generation to this. And what's happened is you have genetic variants that increase lung size or increase spleen size, or in one case in the Himalayas, this very interesting genetic variant that changes the way our bodies make red blood cells in response to oxygen stress. These are all kind of shifting around and create these wonderful adaptations to, in this case, the problem of not being able to get enough oxygen.

Yeah. And also another example in your book about people in Southeast Asia, for example, who kind of live semi-aquatic lives and spend a lot of time free diving. They've also kind of adapted genetically to their environments. Right. It's actually kind of similar to the high altitude problem of not having enough oxygen. Only in this case, these are the folks who spend the large majority of their lives on boats in the ocean rather than on solid land. And they're hunter-gatherers at sea, basically, and they free dive for their food.

And you can imagine there's a lot of selection pressure there, consistent over generations, to be able to do well on less oxygen. And they've got these wonderful genetic adaptations to have a larger spleen. Well, why would you need a spleen that was any larger? Well, the spleen is this reserve fuel tank of red blood cells. Red blood cells are the ones that carry oxygen in your blood to help support a longer dive. And we know that when we look at spleen sizes in this population, and we look at the genetics underlying that, there's been a shift. So

So it's one of these great examples. And our species is full of these wonderful examples of particular responses to particular local challenges. And there's layers of adaptation there because on top of that, you also have the kind of adaptations that happen over a lifetime. You have adaptations that happen over millions of years of our species, right? So we're this sort of interlayered, really complex, but really interesting set of adaptations like that.

What I like about those two examples is that they're quite specific adaptations to the local environment, as you say, so that we should take them seriously as these are things that are improving those people's lives in those places because they need those adaptations. And then if you think about humans, everything we have has taken all those millions of steps to get to us. So I'm just curious.

In that sort of longer sweep of history, what are the big critical junctures where variations in human physiology have occurred that have brought us to the place where we are now, to our big brains and fast metabolisms? I think that if you had to point to one fundamental change, it's this behavioral change to antigen gathering. You've got this sort of dual portfolio strategy. You've got a carnivore and an herbivore basically in the same species sharing food together.

That creates a lot more calories that are available for things like a big brain.

It creates this sort of interdependent need for sociality, for sharing. That doesn't happen elsewhere. It ends up having this sort of snowball effect on brain size. And so over the last two million years, human brains in our lineage had doubled or almost tripled. And so you end up with this interesting dual inheritance. You get all this genetic inheritance, of course, that our species biologically has, the DNA we pass on. We also have this accumulated culture that we pass on.

to each new generation. That fundamental change in how we get our food

ended up having this just knock-on effects throughout everything in terms of metabolism, in terms of our brain, in terms of our sociality, in terms of needing to move, right? Hunting and gathering is a physically active lifestyle. And so that's changed the way our musculoskeletal systems and hearts work, that we are built to now move, made us active in hot climates and changed the way our bodies conserve water and deal with heat. That is the big sea change that's probably responsible for everything that we think about as sort of uniquely human.

All these adaptations that we've kind of living with now must have been successful. They've done something useful for us so that they're still there. But they all have trade-offs, right? Many of them have trade-offs. And the one I liked the most was about the position of the voice box in our bodies. And I think this might sound trivial at first, but it's so important. Why is the voice box where it is in humans? And why is that quite a bad thing, actually?

Yeah, very appropriate to be talking about as we're having this discussion with our voice box. Exactly. Lots of animals can make sounds, of course, and communicate with sounds. But human speech is a very particular thing. And it is a series of vowel sounds chopped up by consonants. And to make those vowel sounds, A-E-I-O-U, you need a vocal tract that's got two components. There's a vertical component that goes from your voice box, which you can kind of feel in your throat,

and goes up to the back of your mouth, behind your tongue. And then this horizontal component that goes the length of your mouth from the back of your tongue out to your lips. Those two components, you sort of shape them differently as you work through your vowels.

And that is the fundamental mechanics of human speech. Well, we're the only species that walks around with our voice boxes so low in our throats to give us this two-component vocal tract. This range. Yeah. Most species are smart enough to have that larynx tucked up much higher, up kind of almost behind their nose.

Why is that smarter? Well, because every time you swallow, whatever you're swallowing, whether it's a drink or food, goes right past that voice box. And you do this sort of intricate dance every time you swallow to make sure that you don't put that bite of food into your lungs or something like that. But of course, it goes wrong all the time. Thousands of people in the U.S. alone choke to death every year. I mean, it's tragic. So imagine that. Why is it

that we're built with this sort of stupid position of our larynx. It's a really dumb... Well, because natural selection has favored that social element of speech, it's been so important to be good at communicating. The natural selection is, the economics of it is, you're willing to put up with the risk of choking.

because the benefits of good communication are so valuable for really intensely social species like us. And so we've evolved these low voice boxes, low in our throat, and the trade-off is, of course, trying not to choke on your dinner when you got to a nice dinner. That's so fascinating. There's clearly a lot of variation across the human species even today, and all sorts of adaptations are probably going on that we don't even know about. With all these adaptive pressures, overall,

How much do these regional differences amount to? Are we more similar or different as a species today? So humans are incredibly genetically similar. And one thing I wanted to try to get across in the book is, yes, we're different from one another. Individuals, of course, each of us is unique. Nobody is the textbook human. But the ways that we're taught to understand those differences, I think, fall short.

Certainly here in the U.S., the way that we're taught about differences, and even aspiring MDs are taught about differences, is a kind of very racialized way to think about it. Well, white people have this kind of a biology. White people have this kind of tendency. I can't imagine a worse way to try to understand or explain human variation. In fact, there's no sort of hard genetic differences between any of the so-called races. Race is a cultural construct, not a biological one.

A better way to think about our diversity is populations around the globe share almost all of their gene pool. The gene pool for your population, for my population,

If they were going to do a Venn diagram, the circles would be almost completely overlapped. There's very few genetic variants in my community that I wouldn't find anywhere else in the globe. But between individuals now, they might be quite different. So for example, let's take an easy one. Let's take blood types, right? The ABO blood type system. Let's say I'm type A.

and somebody else in my community is type b well our community has then at least a's and b's in it and probably would have o's as well right so the a's and b's are all in our community and they'll all be in your community as well those same genetic variants and so in that sense our communities are completely similar even though i as a type a am different than somebody who's type b so

Individually, we're different in some interesting ways. Sometimes you get populations that are a bit different. So we talked about the high altitude adapted folks, or we can talk about skin color as an adaptation to UV light. So there are individual cases where you get these local adaptations happening in particular systems. But it is still the case that those Venn diagrams of the gene pools of all of our communities around the globe are almost completely overlapped with very little differences, right? So I think it's a new way of thinking about diversity.

Thinking about a system by system, thinking about individual to individual, rather than a kind of big categorical broad brush way that doesn't really get it right. Yeah, I mean, you kind of hinted at this already, but I guess humans think about diversity in a slightly different way, in a more visual way, essentially. Whether it's culture or skin color or any of these things. Why do you think that

trying to look at the evolutionary anthropology of humans and the capacity for variation there is important to sort of understand social context today as well. I think once we have a fluency in how our bodies work, the different systems or different organs, how they develop, how they respond to both our genetics and our environment,

With that kind of fluency, you get for free this better understanding of why people differ, right? Because when you understand how a system develops, you understand why it's going to develop slightly differently here versus there or in you versus me. And it's this kind of anthropological view of diversity that I think is much more powerful and much more correct than the kind of broad brush ways that we're often taught about it. Once we understand why I'm unique as a biological individual,

Now I have a better understanding of why I'm different from my neighbor and why people in my community are different from people on the other side of the globe. And so it has these knock-on effects to understanding how our world works. I think it's really fundamentally important. Herman, it's been really great talking to you. And when you've got your next amazing head-turning result out, please come back and tell us all about it. Herman Ponser, it's been a pleasure talking to you. Thank you very much for your time. Thank you. And thank you for listening.

Babbage is produced by Kunal Patel and Jason Hoskin, with mixing and sound design this week by Carla Patella. The executive producer is Hannah Mourinho. I'm Alok Jha, and in London, this is The Economist.