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Why Do We Cook?

  • Posted 10.31.12
  • NOVA scienceNOW

Why are humans the only animals who cook? David Pogue explores this controversial theory and meets scientists studying the biology of digestion with the help of some surprising creatures. What can a python—who likes its dinner raw and furry—teach us about the power of cooking?

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Launch Video Running Time: 13:47

Transcript

Can I Eat That?

PBS Airdate: October 31, 2012

DAVID POGUE: Now that I know a thing or two about how to cook, it makes me wonder why do we even cook at all?

Throughout history, man has sat around a fire, cooking and eating, but we humans are the only animals that eat cooked food. Surely there is a good reason for it.

RICHARD WRANGHAM: Cooked food gives you enormously more energy, and so for a certain amount of food, you get many more calories.

DAVID POGUE: Richard Wrangham is a primatologist in the Department of Human Evolutionary Biology at Harvard. He thinks that cooking was essential to human evolution. He says cooked food is easier to digest, and so, humans evolved to use their food more efficiently. This is the skeleton of an ape, and he is comparing our anatomy with our ape cousins.

RICHARD WRANGHAM: The typical ape has got this very broad rib cage going right out there and flaring out, foreshadowing the fact that it's carrying a big gut down here.

DAVID POGUE: You're not talking about a potbelly, you're talking about…?

RICHARD WRANGHAM: We're talking about the small intestine, the large intestine, all of the stuff that is actually responsible for the digestion.

DAVID POGUE: So the simple invention of cooking produced these enormous changes in our skeletons.

RICHARD WRANGHAM: Yeah. It paid us, once we ate cooked food, to get rid of all of this gut, because that's expensive. So it's efficient to get rid of that.

DAVID POGUE: How can cooking change who we are? Understanding that and how we get energy out of our food is what Stephen Secor studies.

STEPHEN SECOR: They have the potential for killing you, simply from constriction around the neck.

DAVID POGUE: Secor, a biologist at the University of Alabama, works with a creepy, crawly, dangerous array of animals.

STEPHEN SECOR: You need to back up.

DAVID POGUE: He is trying to understand how all animals get the energy they need from what they eat.

Check out how a python chows down.

Here I am. Here snakey, snakey, snakey.

In the case of these guys, the food is very raw. These rats come frozen as snake food.

STEPHEN SECOR: Okay, there we go. There we go. There we go. There we go. There we go.

DAVID POGUE: One of Secor's favorite animals to study is the Burmese python.

It's suppertime.

STEPHEN SECOR: It is.

DAVID POGUE: Down the hatch in one big bite!

Pythons can eat more than a quarter of their body weight at one sitting.

How is the digestive system different from ours?

STEPHEN SECOR: Most of their digestion is identical to ours. It's just all very long and slender.

DAVID POGUE: A python is basically one long gut, so to see inside, we take one to a nearby veterinarian's office for an x-ray.

Hey, look, snakes welcome!

TECHNICIAN: Ready?

STEPHEN SECOR: Yep, yep.

DAVID POGUE: Wow, you see the rat in there!

STEPHEN SECOR: Ah, it's perfect.

DAVID POGUE: Sure enough, there it is: the python's dinner.

STEPHEN SECOR: The head of the rat is in the pit of the python's stomach, and the stomach extends back, and from this point on, that's esophagus.

DAVID POGUE: Inside the stomach, acids break down the rat, bones, blood and all.

Secor x-rayed the python over two weeks. Bit by bit, the rat disappears, and all but the hair is absorbed by the python.

Understanding where the disappearing rat goes can help us understand how our food nourishes us, minus the bones and fur, of course.

To make this point, Secor says, it's useful to compare the rat with a cupcake. After all, to a python, a rat is basically a triple-layer German chocolate cake.

STEPHEN SECOR: Here we have the cupcake and the rat. Both of these have energy stored in them.

DAVID POGUE: Now, even though we don't find these two treats equally appetizing, from the point of view of digestion, what they have in common is that they both are full of potential energy, or calories.

To understand what kind of difference cooking can make to your food, you need to first understand a calorie.

STEPHEN SECOR: Calories represent the amount of fuel that's present with either one of these food items.

DAVID POGUE: Calories are a way of measuring the energy in food, energy your body or a python needs to function.

Think of this cupcake as fuel, like a log on a fire. If we burn it, that fuel will increase the heat of the fire. A calorie is way to represent that increase.

Let's burn the cupcake.

STEPHEN SECOR: Okay.

DAVID POGUE: So it is actually burning…

STEPHEN SECOR: Yes.

DAVID POGUE: …like a charcoal briquette or something.

STEPHEN SECOR: Yes, like a, like a log.

DAVID POGUE: Burning the cupcake like this, in the open air, it's impossible to measure the heat it gives off, so Secor shows me the right way to do it, using a machine called a bomb calorimeter.

Items put in the bomb calorimeter must first be dehydrated, since water doesn't burn. Luckily, Secor is prepared for that.

STEPHEN SECOR: This is a dried rat that has been ground up…all the water out of it…kind of mix it all up and then formed a pellet.

DAVID POGUE: All right, well, bring on the bomb calorimeter.

A portion of the dried rat goes into the bomb calorimeter, where it's burned in a special tank, sensitive enough to measure the heat, or calories, in the rat.

We do the same thing with our pink cupcake: dehydrate it, grind it up, make a pellet and, as the grad students like to say, "bomb it."

Okay, professor. A nation of eaters awaits the results.

The bomb calorimeter says that seven ounces of cupcake has twice as many calories as seven ounces of rat: impressive and disgusting.

Now, let's take it one step further. Those calories come from the basic elements of eating: proteins, carbohydrates, which are simple sugars, and fats. Secor has calculated the percentage of each in our cupcake and rat.

No matter what we eat, whether it be a cupcake or a rat, those are the things your body is going to extract?

STEPHEN SECOR: That's right, and how they differ and how all meals differ is the relative proportion of each of these elements.

DAVID POGUE: What's amazing is the quantity of sugar in this thing. It's almost the entire cupcake by volume. And you know the fat is quite a, quite a dollop, too. And over here we have so much protein and far less sugar and fat. The rat looks like it would be healthier lunch than the cupcake.

STEPHEN SECOR: Right.

DAVID POGUE: Fat, sugar and protein give me the energy to fuel my activity, and Secor can see how much I need by measuring my oxygen use.

It turns out that the act of digesting a meal takes energy, too, like that big plate of barbequed ribs. Even as I lie here, my body is working to break down that dinner.

And that energy I burn digesting takes away from all the fuel in the food. Some of the calories are always lost in the process, and that is where cooking comes in. Cooking made digesting easier.

RICHARD WRANGHAM: When food is cooked, our body doesn't have to work as hard to digest it.

DAVID POGUE: Wrangham says that cooked food gave humans extra energy, compared to their primate relatives.

RICHARD WRANGHAM: And where are we putting it? Here is one big place. This brain is about three to four times the size of this brain.

DAVID POGUE: The human brain requires approximately half a cup of sugars a day to function. That's a lot of calories.

So it was our brain, the largest, proportionally, of any primate, that Wrangham believes benefited most from a nice cooked meal.

It seems we humans have always figured out clever ways to fill up with less effort!

WORKER AT RESTAURANT DRIVE UP WINDOW: Can I take your order?

DAVID POGUE: Can I have the Number One Burger, no skin, bones or feathers, please?

No not that way!

Thanks a lot.

But with tools, like spears or knives, as well as cooking.

Wrangham says getting more energy out of food with less sweat was a key factor in human evolution. Cooking was a real timesaver!

RICHARD WRANGHAM: It takes a lot of time to chew. So if we were a great ape, like a chimpanzee or a gorilla, we estimate that we would have spent about six hours a day just chewing.

DAVID POGUE: What?

RICHARD WRANGHAM: Yeah.

DAVID POGUE: Wow. Their floss budget must have been immense.

RICHARD WRANGHAM: Humans are completely off the curve.

DAVID POGUE: Now, there is one problem with Wrangham's theory: there is no evidence they built fireplaces suitable for cooking until around 400,000 years ago. And we know that the human brain was already evolving, long before that: about 1.8 million years ago.

Wrangham is confident that older evidence of cooking fires will eventually turn up. But, in the meantime, he's hunting for other evidence to support the theory. When he heard about Stephen Secor's work, he wondered if the snakes could help to illuminate just how much energy cooking actually saves.

Secor can easily measure the energy it takes a python to digest food, just like he was able to measure how many calories it took for me to digest that plate of ribs. But there was a problem: pythons don't eat what we do; they like their meals furry.

So how do you make a python eat a steak? That was a challenge for Secor and his grad students. Believe it or not, this is what they figured out. They sewed a rat's face onto a steak.

You have little meat stick rat puppets.

STEPHEN SECOR: That's right.

DAVID POGUE: Why not just take a cooked rat?

STEPHEN SECOR: We wanted to use a food that was similar to what we might be eating. So we need to sort of entice them to eat the steak.

DAVID POGUE: Clearly, science takes ingenuity.

You could tape the face of a cupcake onto a big piece of broccoli and feed it to children.

Success! Once full, on that rat-faced steak, Secor put his python into this Tupperware®, a makeshift oxygen tank, so that he can measure exactly how much oxygen the snake consumes while it's digesting.

Kind of like when I was on the treadmill with the thingy?

STEPHEN SECOR: Same principle.

DAVID POGUE: But they don't make treadmills for snakes, so…

And with that, he can figure out the caloric cost of digesting the raw versus cooked meat. The result? It turns out that cooked steak takes 12 percent less energy for the python to digest than raw steak.

Say what you will, the rat-faced-meat experiment worked.

So what about vegetables? Not even a rat's face will make a python eat broccoli. Fortunately, bearded dragons love vegetables, raw or cooked.

The bearded dragon experiments show that cooked vegetables take 40 percent less energy for them to consume than raw ones.

So the python and the bearded dragon help to show that eating cooked food takes less work to get the energy from the fat, protein and sugar in our food.

There is still the unsolved mystery of when campfires and cooking started, but we know that the impact of cooking has been enormous.

Wrangham says cooking changed many things for humans, by giving us more time and energy to communicate around a fire or even more time to make babies.

RICHARD WRANGHAM: So, cooking really has astonishingly diverse impacts on our lives.

DAVID POGUE: Cooking? A little thing like cooking has produced these enormous specieal changes?

RICHARD WRANGHAM: Cooking seems like a little thing until you go without it. I think of this as the most significant increase in the quality of food in the history of mammals and maybe in the history of life. I mean this was enormous. It has enabled us to dominate the earth.

DAVID POGUE: And it's delicious, too.

Did you know there are ingredients in mother's milk that babies can't even digest?
They're complex sugars called oligosaccharides.
But who could they be feeding?
Bacteria!
Inside the baby's intestine…
…those weird sugars help grow microbes crucial for human survival.
Got to keep those bugs happy…
After all, they make up 90% of the cells in a human body!

Credits

Can I Eat That?

HOST
David Pogue
WRITTEN, PRODUCED AND DIRECTED BY
Doug Hamilton

Nathan Myhrvold Profile

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Jesse Sweet
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Joshua Seftel & Jesse Sweet
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NOVA scienceNOW is a trademark of the WGBH Educational Foundation

NOVA scienceNOW is produced for WGBH/Boston

This material is based upon work supported by the National Science Foundation under Grant No. 0917517. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

© 2012 WGBH Educational Foundation

All rights reserved

Image

(burning cupcake)
© WGBH Educational Foundation

Participants

Stephen Secor
University of Alabama, Tuscaloosa
Richard Wrangham
Harvard University www.harvardscience.harvard.edu/directory/researchers/richard-wrangham

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