Daniel Lieberman, the Harvard evolutionary biologist sometimes credited for sparking the barefoot running revolution, has a new book out—The Story of the Human Body—and it’s a doozy. Lieberman argues that only by looking at human physiology through an evolutionary lens can we truly begin to understand how we get fit, and, consequently, why we get fat.

The Story of the Human Body hits stores this week

That humans are poorly adapted to our modern lifestyle of convenience foods, flat screens, and desk jobs isn’t very controversial. But how we best cope with this new reality often is. Lieberman takes on many popular notions, including barefoot running, the paleo diet, epigenetics, and a host of hot topics ranging from obesity and chronic disease to Nanny State politics. We caught up with the good professor to hear more about his new book and the story of our bodies.

OUTSIDE: I wanted to ask you first to explain more about the provocative idea you bring up early in the book, the notion of "disevolution," which is something we seem to be in the throes of right now.

DANIEL LIEBERMAN: Well, I'm very interested in evolution and medicine, which forms one of the core themes of the book. And some of the focus of evolution and medicine has been: Why do we get sick?

It's not an insight that we, as a society, spend too much time treating the symptoms of diseases rather than their causes. But I guess the argument I'm trying to make is that that, too, has an evolutionary basis. I mean evolution as a perspective helps us inform what's going on, but it's not a traditional kind of evolution, with Darwin and natural selection. This is really a form of cultural evolution.

It seems like one of the key turning points has been this idea that, for many generations, humans have been trying to get enough calories, and now we've suddenly entered this period where we have too many calories.

Mm, it's amazing. And we're just not very well adapted for it.

Do you look at this from an evolutionary perspective and think, wow, we're really in this bizarre and transformative period?

I think so, yeah. One of my jobs is to try to look around at the world we live in, and to think about what's really normal and what's abnormal from an evolutionary perspective. It's normal to think that the world you grow up in is normal, right? We think it's normal to fly in airplanes, drive a car, eat breakfast cereal from a box, and all the other things that you and I probably do—but actually they're abnormal.

Now, just because it's new doesn't mean it's bad, and I think that's probably one of the problems with a simplistic ancestral-health, paleo-diet view. But just because it's new doesn't mean it's good, either.

A lot of things we take for granted make us sick. And we pay a huge price for it. Illustrating that perspective helps us step out of the world we live in and think about it more critically. And that's really the point.

So you’re saying that, basically, the lifestyle that we've come to understand as very normal and commonplace is actually, from an evolutionary perspective, quite abnormal.

Correct. A lot of people might think, oh, I'm going to go back to nature, and what they mean, usually, is to be a farmer. We think of that blissful, pastoral farmer's life as back to nature right? That's actually also abnormal because that's pretty recent. In fact, you could even argue that the bow and arrow is a pretty recent invention. We invented the bow and arrow, and we stopped having to run. And that's only the last 70,000 years.

Evolution is a complicated thing. There's no one point in time when all of a sudden our bodies became normal or abnormal. It's a constantly moving mosaic, which is why I tried to not just start with hunter-gatherers, where I think a lot of paleo-diet, ancestral-health perspectives begin. Hunter-gatherers are the end of an even longer story, and we need to know the whole story. I started arbitrarily with the origins of the human lineage when we diverged from apes, but of course we could go all the way back to fish.

What do you think about the paleo movement, since the back-to-nature idea has moved beyond the farmer and is now the caveman?

Anybody who reads what I wrote carefully will find the critique of the paleo diet in there. But there isn't any one paleo diet. There were many paleo diets, and just because our ancestors ate it doesn't mean it's better for us. After all, one of my key arguments—not an original idea, but I try to drive it home—is that natural selection is not geared toward making us healthy. It's geared toward making us have more babies in a very different context. But the relentless theme that I keep trying to bring up throughout the book is that adaptation is a tricky concept. And there's no simple answer to the question: What are we adapted for?

Early in the book you say that we haven't evolved to be healthy or happy. That struck me because not only do you see a lot of people seeking out solutions to health and fitness, they're also trying to sort out how to be happy. There are some evolutionary factors there as well.

I agree. I don't know the secret to it, either. Certainly having health helps you be happy. In your line of business, in my line of business, we become very aware of the relationship between the mind and the body. They are mutually interactive for many reasons, mostly because the things that make us healthy also make us happier. Physical health and mental health are often both improved by exercise and diet.

You write a bit about how running has influenced the humans we've evolved into today. I just want to make sure I understand one idea in particular, that we're the only animals that have evolved to run long distances in hot weather?

Pretty much, yes. There are other animals that have evolved to run long distances but they do so at night, or dusk or dawn, when it’s cool. We're the only animals that run long distances in the heat. And that gives us a huge advantage. I don't know the last time you tried to run down an antelope or a deer but, should you want to do it, you'd be better off doing it on a hot day.

I haven't chased one recently. But we can do so also because we’re designed to sweat, right?

It's the combination of the ability to cool by sweating and the ability to run at speeds that makes it possible. Because quadrupeds can’t pant when they gallop, they can’t cool themselves. So you basically knock out their thermoregulatory system. If you chase it long enough in the heat, you'll actually drive it into heat stroke. It's called persistence hunting. I can't pretend it's my idea. I've worked a lot on the evolution of running, but other people proposed that first. We just fleshed it out in a famous paper in 2004, the "Born to Run" paper, with Dennis Bramble.

I think that you can't really understand the value of long-distance running, and that's part of the theme that you mentioned earlier—what's normal versus abnormal. When you look around the world today, when you look out your office building, you'll see lots of people walking but you won't see a lot of people running. There are a lot of hunter-gatherer groups that don't run very much, but I'll make a bet that if you could go back 100,000 years you'd see a lot more running going on. Because before bows and arrows, before stone weapons were invented, how else were you going to get dinner? No one's come up with a better idea of why we are so good at running.

Let's talk about barefoot running, since your work pretty much put barefoot running on the map.

Yeah, sometimes I wish I'd never touched the subject! People have so many preconceptions about it and so much anger about this particular issue, which I find interesting. From my perspective, I'm not crazy about it. If you don't want to run barefoot run, don't run barefoot. It's more about how you run than what part of your feet you use.

Do you still find yourself confronted with a lot of controversy about it? It’s ebbed and flowed a bit in terms of its general popularity. And I've had a few conversations with physical therapists who are like, "Oh, god, barefoot running!"

Part of the problem is that it's been approached in a fad-ish way. A lot of people read Chris McDougal's book, Born to Run, which is a terrific book. And they think, oh my gosh, if I take off my shoes, everything will be perfect. I'll suddenly become an ultra-runner, and I'll have this incredible body. And of course, it's not that way. For one, barefoot runners get injured, too. Secondly, if you haven't been running that way your whole life, you're not adapted to it. You need to build up strength in your calf muscles in order to run properly.

But in any kind of fitness or conditioning program you are trying to introduce adaptation through progression.

Absolutely. I see that a lot of the time. People go buy a minimal shoe. I've heard a lot of good things about minimal shoes, but if you've been wearing cushioned, elevated shoes with arch support your whole life, and you suddenly just throw them away and put on a minimal shoe and you go for a 10-mile run, you are going to be very unhappy. And probably soon seeing a physical therapist.

But if you slowly introduce it, and adapt to it, you might benefit from it. On the other hand, if it ain't broke, why fix it? If you aren’t getting injured running in a conventional shoe, there's nothing wrong with it. I'm not opposed to heel striking. I just think that we shouldn't pretend that it's not normal.

Is evolution, or adaptation, or both, accelerating? Are we changing faster than we did in the past?

Well, that's a bit of a debate at the moment. So it depends on the time span you look at. There was a good, popular book a few years ago, The 10,000 Year Explosion, that makes the argument that evolution has actually been accelerating since the emergence of agriculture. There’s a section in my book where I discuss those ideas.

To one extent the answer is yes, and to another extent the answer is no. By having much, much larger population sizes, for natural selection to occur, you need to have intentions that are beneficial or detrimental. And differential reproductive success. One engine that drives at our regeneration is intentions, and the other engine that drives it is competition.

Larger populations create more mutations. So there's more variation out there to act on. But the other side of the coin is that, now, cultural evolution is acting strongly. How much the effects of those variations influence how many offspring you have that survive and reproduce is debatable. One example might be that since the origins of farming there have been lots of selections for genes that affect how we digest carbohydrates. But on the other hand, those diseases that we get from digesting carbohydrates, like Type-2 diabetes don't often affect people until after they've had kids.

It’s kind of an extreme way of saying that natural selection hasn't stopped. And there's more variation out there. But on the other hand, we have so many cultural means to deal with the deleterious effects of our genetic background that it's probably not so important. For example, we know there's a genetic basis for things like myopia and flat feet. Those genes didn't cause people to get myopic or flat footed back in the paleolithic, because they weren't living inside, and reading books, and wearing shoes with arch supports. But the environmental interactions lead to myopia and flat feet. I would be really shocked if people who were myopic or who had flat feet had lower reproductive fitness than people who have normal feet and normal vision. There's no deleterious consequence because in this culture we've got orthotics, and we've got glasses and contact lessons. So natural selection is clearly not acting in those cases.

At times when I was reading the book, I felt like I was projecting forward and wondering if we were all going to end up looking like the cartoon humans in the movie Wall-E.

Oh yeah, I made a mention of that. I think that's where we're headed. Two thirds of Americans are overweight or obese, and about a third of American children are overweight. The numbers don't look good at all.

And other countries are in for a serious crisis. Take India. The journal Nature called it a Type 2 diabetes time bomb. The middle class there has terrible rates of obesity, and diabetes is rising at an alarming rate. One of the scary things about India is that they appear to have less genetic background that protects people. And people are getting it at lower ages there. Also, a lot of the medications that have been developed don't work as effectively on younger individuals.

You talk about the different factors that influence health and fitness, that it really goes beyond diet and exercise to includes genes, your microbiome, stress, and sleep.

Yep. No question about it. I also discuss the hygiene hypothesis, about how our bodies are filled with things that aren't us—about 10 times not you in terms of cells in your body, especially in your gut. Every time you take an antibiotic you change the bacteria in your ecosystem. Sometimes that can have negative consequences. A lot of autoimmune diseases may result from changes in our microbiomes. Certainly, it's been proven to have an effect on obesity.

As for sleep, lack of sleep elevates chronic stress and leads to a series of problems. Sleep also affects your appetite, and the regulation ghrelin and leptin. Everything we talk about is a gene-environment interaction. I focused on the environment’s role, partly because we can't really change our genes. So environment is where we need to focus our efforts.

My sense is that a lot of people feel like they're doing something to combat weight issues and they're frustrated because they’re going to the gym every day and working out for an hour and not getting the results they want. You're suggesting a more comprehensive fitness strategy where all of the factors need to come into line. Changing one or two of them isn't going to really make much of a difference.

I agree with everything you just said. If your sole goal is to lose weight, if that's the reason to exercise, then yes, you are going to be disappointed. It's very hard to lose weight through exercise. But since when was that the only reason to exercise? Physical activity makes you happier, makes you smarter, helps your heart, helps digestion, and a thousand other things.

Second, the data on physical activity helps you keep weight off more than lose it. And third, you're right, there is no magic bullet and part of the problem is that once you're overweight, your body wants to stay that way. That's what we're evolved for.

There's a reason dieting is hard, people who lost weight, were at a reproductive disadvantage most of our evolutionary history. So when you diet, guess what, you exercise less, because you lose the motivation, because you're tired, right? That makes sense, because before the industrialization of food we were programmed to save that energy so we could reproduce better. If people understand the evolutionary story, they can better tackle the problem, they understand their body’s natural response.

This is the genetic destiny we all share, then. Am I understanding it right?

Yeah, absolutely. It’s harder for the person who is already overweight because signaling mechanisms shut off sensitivity to leptin that prevents going into negative energy balance. So we have to stop blaming people who are overweight for being overweight. It's not their fault and we should stop demonizing and ridiculing them. Instead we should understand what they’re going through and how we can help, and that requires an evolutionary perspective.

You get into some ideas at the end of the book about ways to encourage this change.

Part of the book was about that because everybody has strong opinions on what to do. Evolution offers several lessons. One is what kind of environment we’re adapted for, and how there's a complicated trade off for every adaptation.

Secondly, it's important to recognize what we're up against—our evolved instincts. They're almost clichéd, right? If I put celery and a donut in front of you, and we talk for an hour, at some point you are going to reach for the donut before the celery. I would.

If you put a little peanut butter on the celery, maybe I'd go for the celery… Nah, I'd probably still go for the donut. Especially if it's the afternoon, when my brain is really craving the sugar.

Exactly. Those are real instincts, and they need to be understood. And to ask people to suddenly start pretending that their instincts don't exist is just fantasy. There are a few of us who can occasionally do it, but most of us fail most of the time.

So the way I stay fit and healthy is by coercing myself, frankly. I like to run marathons. I sign up for them, not so much because I like to run marathons, but when I sign up for one, it forces me to train because, say, on October 15th I've got to slog through 26 miles. If I didn't, there's no question, here in New England on a Sunday morning in February when it's minus 20 and the roads are covered in ice, ehhh, I'm not going to run.

I have a group of friends I run with so I've now forced myself, I’m accountable. When I go shopping, I always go shopping after I've eaten so I'm a little less likely to do all that craving purchases. We all learn tricks. Fortunately I have enough means and have time to train and run and buy healthy food and not everybody has those opportunities and abilities. And that's why we coerce children. Nobody gives children the choice about what they're going to eat, or at least most people don't.

You bargain and negotiate.

Once you start negotiating, you've lost. The problem is you can't philosophically justify coercion in most cases for adults. In some cases we do, like with seatbelt laws, but they are big battles.

You can't prevent somebody from smoking or eating donuts, but we can't do it on our own, either. We live in a world in which people have provided us all of these comforts and foods that we crave, and our instincts aren't, for the most part, able to handle it.

There is also a lot of deceptive advertising. You know, all those muffin shops claiming their goods are fat free. Technically they're right—these muffins are fat free. But they're 50 percent sucrose, and sucrose is 50 percent fructose, which basically turns straight into fat in your liver. We need laws to prevent that kind of advertising because people don't understand it. We need government on our side in a way that helps us help ourselves, but in a way that respects people's liberties and freedom to do what they want with their lives.

What do you think about things like Mayor Michael Bloomberg's soda ban in New York?

I think that's actually a good example of libertarian paternalism. Because on the one hand, he's not preventing people from drinking soda. He's just saying you can't buy 32-ounce sodas. If you want 32 ounces of soda, you have to buy two. And you can't prevent anyone from doing that. I think people overreacted, as if it was an infringement of their rights. But I think it was a reasonable nudge rather than a shout or a push.

We're in a healthcare crisis. We spend, what, 2 trillion a year in the U.S.? Some of the diseases people get are preventable. Heart attacks, coronary heart disease, strokes—and it's costing a fortune. Can we afford not to take some action? What's going to happen to our economy if we don't start enacting some measures?

It certainly seems like the argument from an evolutionary biology perspective is making a very effective and persuasive case against a lot of this.

Thank you. I also wanted people to understand where they really came from rather than having some kind of artificial idea about cavemen.

Some people just seem to think they should eat more meat. They need some of the actual science behind it and that's in short supply right now.

I also think the paleo movement has done a lot of good, but its become a bit of...it's not quite a clique, but there is a bit of a group think.

My take is that the core community that embraced paleo initially were a little bit more serious about it and probably understood the nuances better. Now that it's more widespread, people are just co-opting it and taking it as dogma.

You know, if you think about it, with 7 billion people on the planet, we're not going to be able to feed them all grass-fed beef. Whether you like it or not, we can't do it. It's just not an option. That's not our solution, and that's not going to help the largest number of people.