Anthropologist Herman Pontzer spends time living among a Hadza hunter-gatherer tribe in order to see if they burn more calories than a typical Westerner.
Herman Pontzer, professor of anthropology at Hunter College in New York, investigates the human and ape evolution. His work incorporates laboratory and field studies of humans and apes, living and extinct, to shed light on our evolutionary past. Most recently Dr. Pontzer has investigated energy expenditure among Hadza hunter-gatherers in northern Tanzania. Follow him @HermanPontzer.
STORY TRANSCRIPT
Humans are weird. We don't think we're weird. We're biased. But imagine just for a second how you look to any other normal animal. Big, bulbous head, naked, sweaty skin, walking around on two legs, your bits flopping about. It's disgusting. It's disgusting. We know this inherently because we're the only species that feels the need to cover ourselves in clothing.
And secondly, you ever think about anytime you hear about a case of bestiality it's always the humans that initiate it.
I'm a biological anthropologist, which means my job is to figure out how humans got to be such oddities. How evolution shaped our biology and our bodies. And that is how I ended up driving a 30-year-old Land Rover covered in diesel fuel, into the teeth of this raging savanna fire in northern Tanzania.
I was in the middle of a two-month stint living with the Hadza, one of the last populations of hunter‑gatherers on the planet. Nobody had ever measured how many calories you burn if you're a hunter-gatherer. And to my buddy and fellow anthropologist Dave and I, that seemed like an obvious screamingly important thing to do.
From an evolutionary perspective, life is just a game of turning energy into kids. So you can't understand anything about a species until you understand how it uses its energy.
And since humans evolved as hunter-gatherers, we were missing something really fundamental about humans if we didn't understand how hunter-gatherers use energy.
We're also missing something really important in public health because it's commonly assumed that one of the reasons that we struggle with diabetes and obesity and other metabolic disease in the west is that our cushy urban lifestyles don't burn as many calories as our hunter‑gatherer ancestors did. A typical American adult burns about 2500 calories a day but estimates for hunter-gatherer energy expenditures are 3,000, even more, calories a day.
But those are just estimates so this might be a big problem and something we need to tackle. But without real data, there's no way to get a handle on that and know.
The plan was pretty simple. We'd go live with the Hadza and we'd have them drink some water that was enriched in these isotopes of hydrogen and oxygen. Completely safe. Completely expensive.
And what you would do then is after they drink some of this water, we would collect urine samples over every couple of days for about two weeks. And by analyzing the levels of those isotopes in the urine samples, we could calculate how much carbon dioxide they produce every day and that would tell us how many calories they're burning because you can't burn calories without making carbon dioxide.
Now, the one little wrinkle was that we had to keep the urine samples frozen. And for that, we were going to use liquid nitrogen. Perhaps that seems like overkill, but when you're in the middle of the savanna with no electricity and no obvious way to keep things cold, liquid nitrogen is the way to go.
And plus, cattle husbandry, turns out, is huge business in East Africa, at places like awash in bull semen which they keep on liquid nitrogen. So it's actually easier to get a gallon of liquid nitrogen than a good cappuccino in most of East Africa.
So we knew that the Hadza would burn a lot more calories than we do in the west. The question was really just how much. Life is really strenuous for the Hadza. They don't have any agriculture, no domesticated crops or animals. They don't have any machines. They don't have any modern conveniences. No electricity or plumbing, anything like that.
Instead they wake up every morning and they comb the rocky savanna around them to get food to eat that day. So men go out and hunt wild game with bows and arrows that they fashion themselves. Women go out and look for wild plant foods. They dig for tubers or collect berries, often with a kid on their back the whole day.
And at the end of the day they come back to camp and share the food they got, sitting around their grass huts having dinner. It's an incredibly strenuous, challenging lifestyle.
But a lot like the Amish here in the states, they know about the outside world but the Hadza are really proud of their culture. They really love their old traditions and they stay with them. And that's a boon to people like me who are interested in our species’ past.
The Hadza are incredibly generous to let us live with them and do this research and they are also incredibly badass. Nothing, I can tell you this from experience, nothing makes you feel less adequate as a man than sitting there eating your bowl of instant oatmeal while five Hadza of guys come back with a freshly killed antelope that they stole from a pride of lions, because the lions are afraid of them.
Up until the fire everything had been going great that season. Dave and I had talked another buddy, Brian, and another, he's also an anthropologist, into leading the field operations.
Brian is a Hadza expert. He's lived with them on and off for years. The deal was Dave and I, who had done field work but nothing with the Hadza, we would focus on getting the energetic measurements. Brian would take care of everything else. Any problems arose, it was up to Brian to lead the way and he'd know what to do.
Up to that point, everything had been going great, though. There really weren't any snags. The only one funny thing that happened was a tank of diesel fuel in the back of one of the Land Rovers had sprung a leak and it just spilled diesel fuel all over the back of the Land Rover, just soaked the whole thing.
And we thought, “Well, as long as we're not dumb enough to get this thing near open flames, we're fine.” Hahaha.
Well, the fire came out of nowhere and Brian that morning had conveniently left to go track a wounded giraffe with some Hadza guys. Typical Wednesday morning, am I right?
And the landscape there is just this golden sea of tall, dry grass. The entire thing is incredibly flammable. You are just waiting to get burned alive as this wall of fire comes towards us. It caught Dave and me totally by surprise.
We look at each other and we realize everything we have is flammable. The tents, the sleeping bags, the computers, the solar panels. Not to mention the Land Rovers, of course, which are your lifeline to the outside world. And you know what fire would do to this five gallon cocktail of liquid nitrogen and Hadza pee. I mean the whole project is about to just go poof.
And we thought what the hell are we going to do? We are in the middle of… this is all going to be fire very soon. What are we going to do? Where can we go? There's no escape.
We realized the only place that wouldn't burn was where it had already burnt. So all we had to do was drive through the fire to get to where it had already burnt. That seemed like the best option. I mean when that's the best option, that's tough.
So we just took everything, all the important stuff anyway, and just chucked it all in the Land Rovers and just aimed for a break in the firewall and just hoped we wouldn't explode, and drove through. And it worked. We didn't explode. I'm here.
And we're getting out of the Land Rovers feeling pretty good about ourselves, having saved the day without Brian's help. Dave and I look at each other pretty happy, pretty satisfied. We look back towards the Hadza village as the fire kind of sweeps in and that's when we saw the Hadza houses, those little grass huts start going up like match heads. Just pfff-pfff-pfff. We were just in disbelief.
We ran over to the camp as quick as we could and there are the Hadza women gossiping, chatting, laughing. They'd seen that fire come in long before and they'd done what any smart Hadza woman would do. They'd went into their houses, grabbed all their possessions, which they could do like this, in two arms, and taken them out to some flat rocks that couldn't possibly burn near camp. They are fine.
In Hadza Land you can rebuild your house in about a day, but replacing that nice cotton t‑shirt, that's a pain in the butt. So life lesson and priorities from the Hadza women there.
So we survived the fire and we did hit some other snags that summer. We had a Land Rover break down on a resupply in the middle of nowhere. The liquid nitrogen kept running low because those tanks are built for air conditioned laboratories not hot equatorial sun. We had to drive to Kenya to ship the samples out.
But you know, time goes on and eventually it's the day that you're packing up and leaving camp. Then it's the day that you're getting on the airplane and you're flying through Amsterdam having that nice cappuccino. And you're back home and you slip back into your old routine. Summer kind of works its way into fall, classes start up. So I'm teaching classes that fall.
Then it's winter break in February. Snow is on the ground, and I get an email from the isotope lab that had analyzed, finally, all of those urine samples. And there in an email attachment were all the answers. There's the data. There's distilled, the entire project distilled into a little Excel file. All the calories per day for all the Hadza men and women that participated in the study. This was it. This was the reason for doing all this.
It was too much. It's overwhelming. I couldn't open it up right away so I cleaned my office and alphabetized my bookshelves and everything else.
Finally, it's time to reckon with this. So I sat down and I pulled up, first thing I did I pulled up some comparison data for folks from the U.S. and Europe, like us here in this room. And I had their energy expenditures all mapped out and I had that nice 2,500 calories a day average that you'd expect for folks like us. And then I got the Hadza stuff ready.
And this was going to be big. Was it going to be 3,000 calories? 4,000? I didn't know. Was the computer going to explode from all the calories?
A couple of clicks and there it was. No difference. No difference at all. Same 2500 calories that we burn here in the west. I couldn't believe it. I was sort of nauseous.
You know, I'm a scientist. We know how to massage data, right? So I'm correcting for body size and I'm correcting for sex and I'm correcting for age and I'm doing all the… nothing. Nothing. Hadza are completely indistinguishable from you and me.
We went to all that trouble, three years to get this funding and get the permits for this project, all that trouble in the field, all the generosity and time from the Hadza themselves, of course, surviving a wildfire, all to get energy expenditures for Hadza hunter-gatherers, and apparently, I could have gotten 30 people off the street and gotten the same damn answer.
There's a term of art in science that kind of captures that crushing hopelessness you get when an experiment doesn't work. It's called negative results. These were the most negative results I'd ever had. I was just I didn't know what to do.
And then slowly, a light flickered on and I realized these were the coolest results I could have gotten. The Hadza were telling us something really fundamental and important about the way our bodies work. That no matter how different the lifestyles were, despite these radical differences in lifestyle, that just under the surface, our bodies were working really hard to keep everything running the same for the Hadza and for us in the west and for everybody else.
We were going to have to rethink what we thought we knew about hunter-gatherers and about hunter-gatherer energetics and ecology in our hunter-gatherer past. We were going to have to rethink what we knew, what we thought we knew about obesity. We're constantly barraged with this message of we need to exercise more to stay thin. We need to adopt a more hunter‑gatherer-like lifestyle, more physical activity. And it's absolutely true. Exercise is fantastic for you. You should do more of it. But it's not enough.
What the Hadza data were telling us is you could be as active as a Hadza hunter gatherer and you're still not going to burn off the extra calories. Our bodies are working under the surface against that.
How do we do it? How do our bodies adapt to these radically different lifestyles to keep everything running the same? How do our bodies know in the first place how many calories you're supposed to burn? I had no idea. I was in uncharted territory right there in the office and this was going to be a lot of fun.
Thank you.