Duke University Professor Herman Pontzer, PhD ’06, says that a deeper understanding of how our bodies evolved and how that process shapes our biology can help us better take charge of our health.
We all want to live as long and as well as possible. Diet and exercise are crucial, but how can we make sense of the flood of information, which sometimes seems to contradict itself? More importantly, how can we adapt the information in ways that work for us as individuals?
Know thyself, answers Duke University Professor Herman Pontzer, PhD ’06. Every body has a story, he asserts in his new book, Adaptable. So does every part of our body. The main characters are our organs and systems. The themes and plot are a mishmash of genes and our environment. The result is an astonishing amount of diversity across humanity, united by our common ability to adapt over time and place. Pontzer says that a deeper understanding of how our bodies evolved and how that process shapes our biology can help us better take charge of our health.
This transcript has been edited for clarity and correctness.
Your book, Adaptable, begins like a good murder mystery: with a dead body. I'd love it if you could just tell the story of your experience as an “interloper” at a [Harvard] Medical School dissection while you were studying at Harvard Griffin GSAS. What was the realization that you had that eventually played out in your new book?
So, my first semester at Harvard as a grad student or PhD student, I had the luxury, the privilege of being able to take gross anatomy at the Harvard Medical School with the incoming Harvard Medical School class. And so, I was never intending to be a doctor. I worked as an EMT for a few years, at the end of college, and then, you know, afterwards. But I knew I wasn't gonna be in the medical field.
But, you know, I've always just been intrigued about how bodies work, and I knew I was launching this career into a whole career spent looking at human bodies and thinking about how they work. And how could I not take the opportunity to really get down to the details and disassemble a human, and see the parts, right? And so, I jumped at the chance, and it was it was eye opening, for all the sort of all the reasons you can imagine.
The person who led that course for so long was a professor in biology at Harvard, named Farris Jenkins, wonderful man, an evolutionary biologist. Now, why do you have an evolutionary biologist teaching a human anatomy class? Isn't that strange? His focus was not humans; his research focus was early mammals, among other things. Well, because it helps to understand from an evolutionary perspective how everything developed, how it got to be the way it is, how it all works. So that was kind of an eye-opening thing.
Eye opening thing number two was that, as you work your way into the body, you are immediately frustrated daily by the fact that what you're looking at doesn't look like the book. We've got these old textbooks that are supposed to work us through. The sections are set up like chapters. Like, let's look at the abdomen this day. Let's look at the heart. Let's look at whatever. And, you know, nearly every day, you are encountering variations in this person that you were assigned—and, by the way, I really appreciate the gift of that person donating themselves for this. I mean, we couldn't do it without these generous folks.
But, you know, as soon as you get under the skin, it doesn't look like the book. Sometimes it does. Sure. But often you find these structures that are different, and that is why you do it. In this world of CGI and all this different great computer modeling and visualization software, you can go online and get yourself a free app. It'll help you work through the human body. You can see every structure and thing that's there. But guess what? That's a fiction. Dissection in real life with a real cadaver is how you learn. That's what I took away from it anyway. Just how different we all are. Even though, of course, on the surface, we're all quite similar and different too.
So it's this great tension that you walk out of this class with. Yes, we're all the same. Yes, we all have a shared evolutionary history. Yes, things generally work a certain way. And yet, we are also all unique snowflakes who all have all these differences. That's the tension. How do you understand that? And so that has been motivating for my career.
It sounds like that fascination with your exposure to the reality of human physiology is the undercurrent in this book.
Oh, absolutely. I mean, I just am overwhelmed all the time at the kind of just how cool the body is. There's so many interesting things going on, complexity, you know, harmony, integration, it's all there. And, you know, I guess that's another reason I wrote the book. I just want to share that joy and that kind of wonder.
But then it does leave us with the hard question: How do we understand and how do we make sense of the fact that you're different than me, I'm different from everybody in the world, two identical twins are different from each other, and yet we're also all humans, and we've all got the basic laundry list of parts [that] is more or less the same for everybody. We all have this shared history. How do we deal with that tension? And again, that kind of spills out in different ways into how we think about how society works, right? And so, we have to begin with the building blocks, how do the systems work and that allows us to kind of build ourselves up and have good answers or at least a good evidence base to have a better conversation about these big questions.
I read you in this book as trying to, as you were starting to do just there, move beyond the kind of nature versus nurture debate and show how both really combine to shape our bodies and our health. I'd love it if you could talk about how genes and environment interact when our brains visit the supermarket.
Speaker 1: Yeah. Well, you know, I mean, that's exactly right. That's a great place where we see this in real life. You know, [in the] early post-Darwin days of human biology and anthropology, nature ruled everything. That got it to a lot of ugly places, including the eugenics movement that became the Holocaust.
I mean, there's so much ugliness that came from the genetic, deterministic, all-nature [perspective]. We can't get away from that point of view of how our bodies work. The pendulum swung, I think, and did a lot of good and said, No. No. No. Nature is actually shaping our bodies in ways that are really important, and so let's invest in early childhood education, those kinds of things. Right? Let's understand that what we think are deep, immutable biological differences are actually usually cultural or environmental differences. I would say we're now in a third, moment, a third part of how we understand the body and and let's call it a personalized way. So if we go from nature to nurture to, okay, unique, how does my individual body work?
And you can get your retail genetics looked at. There’s no better time to measure all your environmental influences than with all the wearables we have. And people are beginning to say, okay. It's nature and nurture together. How does that work for me? And, you know, we can experience it when we go to the supermarket.
Our brains are built to love salt and sweet and fat. We don't have to be taught that. Now, some of us, depending on the genes we're dealt, right, what gene variants did you happen to get from mom and dad, are lit up a little bit more or light up a little bit less, depending on how we get those nutrients. Right? We also have different nurtures, different environments. So, you know, what tastes good to you? What were you told tastes good? And, you know, you look at a package and, in moments that you can't even really conceptualize or experience consciously, there is a wash of response. The stimulus and response of your brain. And the question is, do you put the package in this basket or not? Do you put it in your cart and go check out, or do you say Not today? I'm gonna go get something else.
That is the struggle that we all face on some level. Do you put lots of healthy stuff in your cart? Do you not? Now, let's also be honest that there's an economic factor. Do you even get to go to a place that has healthy food? Are you making a wage that allows you to afford these things? So let's not ignore those issues. But, you know, but then also, let's say you do have those choices. What choices do you make? That's nature and nurture right there.
And, you know, notice we haven't said anything about race. We haven't said anything about ancestry. Because that set of gene variants has nothing to do with the color of your skin.
That set of gene variants that are affecting the way our brains work has nothing to do with where our great-grandparents came from. And so, when we think about human variation, we really have to think system by system like this. How does my digestive system work? How do I interact with food? How do those gene variants work? And when we have a discussion about how our muscles work or how our immune systems work, we're gonna have another discussion there, they're gonna be system by system, and that's really a more fruitful way to ask these questions. The way we often talk about human variation right now, which is Oh, well, if I'm white, I'm like this. If I'm Black, I'm like that. So we can get away from that not very helpful way of thinking about human diversity [and move] into better ways.
I'd love to talk about a couple more examples of the incredible human diversity and adaptability that you cover in your research. You talk about people who live in the mountains, like the Andes and the Himalayas. And then kind of on the other end, people who are the free divers of Southeast Asia. Talk to me about how those exemplify the point and the main themes of adaptable.
One of the questions that comes up again and again in the book is, why, across the room or across the globe, do we see differences in how people look and how their bodies work? And the story again and again is most of this variation isn't particularly meaningful. So, things like the shape of your head. Is it wide or is it narrow? Those kinds of things we know are just noise in the system. And most of the differences that we see superficially are just exactly that. The just-so stories we tell about why people are different, usually, there's not a whole lot there.
Now, interestingly enough, when we have populations move to a new area and experience really strong selection pressures, the environment's really pushing around who survives the best and who has the most kids because that's what evolution really cares about. And there are some gene variants that really are helpful in that environment and some that aren't as helpful.
Now we have the potential to see what I'll call local adaptations. For that to really happen, you have to have an environmental pressure that's lasting many, many generations, stable, and local. That's rarely the case, but sometimes it happens.
Well, it happens when we move to the mountains. And so populations have moved into high altitude in the Andes, like you say, in the Himalaya, in the Ethiopian Plateau. And every one of them becomes a little bit isolated up there and also experiences the same pressure, which is that there's not enough oxygen to breathe. You need oxygen. So how do you deal with that? Evolution has generated different solutions. [There are] different ways of responding and making sure you can carry enough oxygen in your blood with enough red blood cells.
There's this amazing story in the Himalayas, specifically. One thing that anybody's body will do if you go to altitude, and this is whatever your ancestry is, your body will make more red blood cells to try to carry more oxygen. Your red blood cells carry oxygen. If you're oxygen-starved, you'll make more red blood cells. If you make too many, your blood gets a little too thick, and that can lead to what's called altitude sickness.
There's this gene variant . . . everybody carries it essentially in the Himalayas. It's not very common anywhere else, but it's very common there. There's one gene variant that regulates how many red blood cells the body makes so you don't overproduce them. Folks in Nepal and in the Himalayas, they live their lives. They get enough oxygen. They're adapted to do that very well. They don't overproduce, and they don't have as many issues with altitude sickness as people, for example, in the Andes tend to have.
Where do they get that gene variant? They got that gene variant from a past mating event with a whole other species of human, called the Denisovan. There's this amazing evolutionary story there. As our species was successful and evolved in Africa and then migrated to Europe and into Asia, we met these other species: Neanderthals, for example, you've probably heard of; Denisovans, which people might not have heard of. “Admixed” is the word that we use for the mating events with these groups. And we picked up some genes. Most of these genes don't seem to have any big effect, but this one does just in this one particular case. And so it probably had no effect on any, you know, survival or reproduction for a long time until the downstream generations later, people started to go up into the Himalaya. And if you had that variant that they got from the Denisovans, there you go. So, it's a crazy story, you know, with multiple timelines going on.
Now, how does that relate to people who spend their lives in the ocean? You think it'd be the opposite problem, right? Because it's the opposite of altitude.
But actually, it's the same problem. Human populations in Southeast Asia, in the Pacific, on boats, and at sea rarely come to land, forage underwater. Well, guess what? There's no oxygen for you to breathe underwater either. And so there's been the same selection pressure. How do you get enough oxygen?
In this one population called the Sama, we see a gene variant that increases the size of the spleen being very common there. Why was that gene variant favored? Well, because your spleen is a sort of reserve tank of red blood cells. We all use it that way, but we haven't all been through the selective pressure of getting a slightly bigger one to have a bigger reserve. So, yeah, wonderful story of dealing with oxygen levels across different populations there.
To get back to something that you'd started to talk about before, humans historically have often conflated cultural constructs—particularly around race, ethnicity, and gender—with biological differences. I'd love it if you could talk a little bit about the dangers of that way of looking at diversity and how Adaptable really tries to flip that script.
Again, I think we try to understand why people are different, why we see their differences, and how we're all unique. I think that's a normal human thing to wonder. And without an understanding of how our biology worked, people have come up with a bunch of bad ways historically of understanding diversity, unhelpful ways.
And often, the way that we understand diversity has been used by the powerful to keep people down. The classic example of this in the US is the way we talk about race and the way that race was used to divide people up and create these hard categories. That racial way of thinking about the world is really just, truly, done to keep one group enslaved to the group that was in power. But it's talked about as though it's a real biological categorization.
Now, you know, in today's world, we still use those terms: Black, white. But, you know . . . if you look at human biology, if you look at blood types, if you look at any of our physiological systems, none of them are categorized or break down along these racial lines. Even skin color, which is used as one biological marker of race in this country, really doesn't work that way. There aren't hard edges on it if you're dark-skinned or light-skinned. There's everything in between, of course.
And so, you know, if we take this racial view of our diversity and we say, Look, in my world, there are categories. You're either this or you're that. And you let yourself believe that is telling you something meaningful about [a person’s] biology and about the way their bodies work . . . it's not true for one thing. And because it's not true, it's completely unhelpful for, again, tackling these big societal problems.
And so, I try to kinda break down all the reasons that it's not a good way of thinking about the world in the book, and give a better way of thinking about our diversity.
And isn't it true that, actually, most of the genetic diversity that you write about in Adaptable is within races and ethnicities?
Yeah . . . if you look at genetic differences between two individuals within a population, you're more likely to see bigger variation between individuals within a group than you are to see between groups.
I work in Africa, for example, in Kenya and in Tanzania. And I talk in the book about working with the population in Kenya. If you look at the genes that affect body size and proportion . . . the tall people in these hot environments tend to be taller and thinner, that's true across the board, regardless of what continent you're on. If you look at those genetic variants, the folks we work with, you know, I'm more similar genetically probably to the folks I work with who are coming out of Nairobi and don't share those same gene variants for being tall and thin. But if we take all of us to the US . . . we'd lump the tall, thin folks in Northern Kenya in the same Black race as my colleagues from Nairobi, even though that's actually not how the genetics sort out at all. That's not how the relatedness sources out genetically.
And it's not useful anyway because all we're talking about in that case is sort of skin color, which is a whole other . . . aspect of our biological diversity. Skin color is, of course, a biological trait. [But] when we start talking about how things break down within versus between groups, we see that race doesn't mean anything. This category doesn't mean anything. And even when we try to apply them in a kind of a practical way to understand variation in different traits, it also breaks down. So let's try to move forward with a better way of doing it.