Did Cooking Give Humans An Evolutionary Edge?

In Catching Fire: How Cooking Made Us Human, primatologist Richard Wrangham argues that cooking gave early humans an advantage over other primates, leading to larger brains and more free time. Wrangham discusses his theory, and why Homo sapiens can't live on raw food alone.

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PAUL RAEBURN, host:

From NPR News, this is SCIENCE FRIDAY. I'm Paul Raeburn.

This summer, while you're helping yourself to burgers and hot dogs and corn off the barbecue, stop for a second to think about this: Have you ever seen a chimp or a gorilla flipping burgers at the grill in all those hours of animal films on television ever? Probably not.

That's because other primates don't barbecue their food or boil it or broil it or sauté it or any of those things. Cooking, it turns out, is a uniquely human thing, but my next guest says it's not just unique to humans, it's essential. It's what made us human, and he argues that this custom of cooking our food has not only changed our bodies over the years, giving us smaller mouths and smaller guts, he says it's given us an evolutionary advantage: bigger brains, more time to use those brains and less time wasting time foraging and chewing all day long.

For the rest of the hour, we'll be talking about how cooking made us human, and give us a call. We'd like to hear from you and hear your questions. The number is 800-989-8255. That's 1-800-989-TALK.

Now I'd like to introduce my guest, Richard Wrangham, and we'll have some - we'll be talking about cooking with my guest Richard Wrangham, the author of "Catching Fire: How Cooking Made Us Human," who will be with us shortly. He is the director of the Kibale Chimpanzee Project in Uganda and Ruth Moore Professor of Biological Anthropology and Curator of Primate Behavioral Biology at Harvard University.

While we're waiting for him, his new book about cooking and how it made us human is just out. So please check that out if you're interested in what he has to say.

I think we have him. Dr. Wrangham, are you with us?

Dr. RICHARD WRANGHAM (Director, Kibale Chimpanzee Project; Ruth Moore Professor of Biological Anthropology, Harvard University): I am, Paul, thanks a lot.

RAEBURN: Thanks for joining us.

So now, I've given a bit of an introduction, which you might not have heard, about how cooking is not only unique to humans but made us human, and before we get to that argument and this very interesting new hypothesis of yours, do we have any evidence on how humans first began to cook?

Dr. WRANGHAM: Good heavens, no.

(Soundbite of laughter)

Dr. WRANGHAM: At all. It's completely lost in the mists of time, but we do have evidence is that our ancestors would have enjoyed cooked food as soon as they experienced it. That is to say if they had the opportunity to sit next to a fire or to see the products of a fire and take food after it had been heated, there is very little doubt that they would have immediately appreciated it. And the reason for saying that is we have done tests on the great apes, and the great apes uniformly show a preference for cooked food over raw or sometimes have no preference for cooked over raw in the case of one or two things, but they never prefer raw to cooked. And it seems likely that our ancestors would have been the same.

Put them next to a fire, drop something in by accident, and bingo, cooking gets going.

RAEBURN: Now, do we think that's - I mean, do we guess that somebody dropped meat in the fire or that there was a forest fire, and animals were burned? What do we think might have happened?

Dr. WRANGHAM: Well, I mean, that's all very speculative, of course. We can look at chimpanzees, and we do see a little bit of food processing by them, but not with fire - they will mash their foods. But what they will do in one place in West Africa is, after a fire has gone through and has baked some seeds of a species of tree that these chimpanzees do not normally eat when they're raw - do not eat at all, in fact, when they're raw - they will eat them after they're cooked.

So they understand that it's worth going to a place after a fire has swept through, and it's possible that that's one of the kinds of ways in which our ancestors might have learned.

RAEBURN: Now, somewhere along the line, there's this great difference between these very close relatives of ours, the chimps and apes, and humans - somewhere, these lineages split in evolutionary time, and one lineage started to cook, and the other didn't.

Now, you talk in the book about two particularly significant periods of development of human ancestors. Can you tell us a bit about that?

Dr. WRANGHAM: Well, yes. I mean, until we have the period of around two million years ago, our ancestors are pretty well known as australopithecines, which were chimpanzee-sized creatures that were not very different from a chimpanzee standing upright.

They walked bipedal. They had brains a little bit bigger than chimpanzees, but they were basically undoubtedly eating the same sorts of foods as chimps or gorillas: raw foods and a mixtures of fruits and veg and maybe occasional bits of meat.

And then around 2.5 million years ago, we have the first of the great transitions, which is that the australopithecines gave way to a species that is variably called Homo habilis or Australopithecus habilis, the uncertainty reflecting the fact that people don't know whether to call it more ape-like, Australopithecine, or human-like, Homo.

RAEBURN: We're getting close to the dividing line here at this point.

Dr. WRANGHAM: Exactly. This was kind of the missing link. This was the species that was still pretty small but was getting a bigger brain, and it was associated in time with tools that could have been used for cutting meat off bones, and so they were almost certainly meat-eaters.

And then another half million years and more pass, and we get to around 1.9 million years ago, and that's when you have the first species that everybody is happy to put into our genus, Homo. Homo erectus, a species about our size, although variable, and the first one, one might say, that could walk down a street in a modern city and go into a store and get some clothes off the peg.

(Soundbite of laughter)

RAEBURN: They didn't prefer designer clothes, as far as we know.

(Soundbite of laughter)

Dr. WRANGHAM: Right.

(Soundbite of laughter)

Dr. WRANGHAM: Of course, you know, they might have been hairy, but I don't think they were. At any rate, Homo erectus - I mean, some people regard it as so similar to ourselves that they call it Homo sapiens, some professional anthropologists.

Most people recognize it as a different species on the basis of its smaller brain and somewhat thicker bones and so on, but it was pretty much like us. And so the big question about where do we come from and why did these changes happen from essentially a chimpanzee-like creature standing upright all the way to an early, primitive version of humans, concerns those two changes. So one into the habilis type, and then from habilis to Homo erectus, and that's where all the action lies.

RAEBURN: And that's where cooking came into play.

Dr. WRANGHAM: Well, for my money, it is. Undoubtedly, meat-eating was a hugely important part of all this. And the traditional view is that was all there is to say, that our ancestors became meat-eaters, and the rest followed from there.

But here's the thing. Nowadays, we look at people, and we find that if people go onto a diet of raw food, then something peculiar happens -which is that unlike every other animal, they do not thrive in terms of getting really adequate energy. And there is a pretty clear reason for this, which is that our species has a very odd type of digestive system.

It's less than two-thirds of the size of the digestive system if we were a great ape - like a chimpanzee or a gorilla - in relationship to our body size. And so we have somehow, and for some reason, adapted to having a small gut - and we also have small teeth and small mouths - all of which indicates that we, as a species, have adapted to a diet which is very high quality, and we don't have to put large amounts through our gut and retain them and ferment them for many, many hours.

Well, what kind of diet is that? It seems very clear that cooking is responsible for increasing the quality of our diet in this way. So then one can say, well, okay, when did we get these adaptations, the small gut, the small teeth, the small mouth? And the answer is 1.8, 1.9 million years ago with the evolution of Homo erectus.

So if cooking is what restricts us as a result of our small diet - our small guts, excuse me - to a high-quality diet, then surely that's when cooking must have begun.

So I now like to think that the way to conceive of the pattern of human evolution is in these two important jumps. One is the acquisition of meat-eating, around 2.5 million years ago, where a serious increase in the amount of meat eaten led to important biological changes, including the initiation of a larger brain; and then with the full hominization at 1.9. That's when, surely, cooking must have begun.

RAEBURN: So others have said, if I understand correctly, that it was meat-eating or meat-eating and hunting that led to this change or it encouraged or accelerated this change. You're saying it's cooking per se, not just raw meat wouldn't have done it.

Dr. WRANGHAM: Yes. I mean, one of the problems with the meat-eating hypothesis is the one that I just mentioned, that you're asking it to do two things, to explain two kinds of transition. But another is that people have not given consideration to the difficulty of eating raw meat.

You know, I spent a lot of time watching chimpanzees, and even chimpanzees find it difficult to eat raw meat, even though they've got, you know, much bigger jaws than ourselves and big teeth. But they eat rare meat pretty slowly. They eat it so slowly that as they chew and chew and chew, the calculation of the rates of calories taken in per minute or hour is not very different from eating their not-very-high-quality fruit.

The difficulty with meat is that it's tough when it's raw. And I think that even when our early ancestors were taking this very important step of adding a significant amount of this high-quality food to their diet, they must have been processing it. And I think a very reasonable idea here, which should be archeologically testable, is that what the habilines were doing before the evolution of Homo erectus, when they were cutting meat off bones, undoubtedly, I bet that they were pounding it with rocks.

And we have lots of fist-sized hammer stones that they were clearly using for something at that time, and that would seem very reasonable. Because if you pound meat, then just like making steak tartare, just like making ground beef, it makes it much easier to chew and - actually, as we have seen with tests with pythons - it reduces the metabolic costs that the eater must pay for digesting the food. It actually gives you a relatively greater amount of calories if you can process your food in that way.

RAEBURN: So, you - in other words, the raw food. Is it the chewing, or is it something that has to happen in the stomach? Where are those extra calories going?

Dr. WRANGHAM: Well, there are two big reasons why it pays to cook your food. One is that it increases the proportion of the nutrients that you actually digest, because for raw food, there is a significant probability that a particular nutrient will pass through your gut undigested.

The amazing thing about this is that, until recently, this had not been widely appreciated because most people had looked at the difference between the amount of nutrient that you eat in a mouthful and the amount that exits in your feces to try and work out how much of it you had digested. But this is not quite the right way to do it. That - call that measure fecal digestibility. And you might find that all of the starch, say, that you eat might have been disappeared by the time it reaches the feces, which makes it look as though it's 100 percent digestible.

But the reason it might not be is that in our large intestines, in our colons, we have some 400 or 500 species of bacteria and protozoa that are themselves hungry, as it were. They are going to metabolize any food that comes through into that area. And depending on what the nutrient is, our bodies may not be able to use that at all. I mean, in the case of protein, for example, any protein that goes from the end of the small intestine into the large intestine is completely useless to us metabolically. It is digested by the bacteria and transformed into chemicals that we cannot use.

So, the only way to assess the impact of cooking on digestibility is to look at what happens to the food by the time it reaches the end of the small intestine, before it goes into the large intestine. That is, of course, a great, great difficulty because it hurts if people dive into your guts and extract your food.

(Soundbite of laughter)

Dr. WRANGHAM: But there is a way to do it, and that is to take advantage of people who've the misfortune of losing their large intestine, or a lot of it. And they end up with an ileostomy, a bag at the end of the small intestine that lies on the surface of the abdomen, and this is the way that they pass their food. And the researcher can then get permission to extract this effluent from every 15 minutes, or whatever it is, and then see how much of the food is digested by the time it gets through the end of the small intestine.

The results have been fascinating. There is a study by some Belgian gastrointestinal physiologists on eggs. And what they discovered was that when you cook your eggs, then almost all of the protein is digested. So it's digested to the point of about 94 percent, whereas if it is eaten raw, then only 55 to 64 percent of it is digested and the rest is lost.

RAEBURN: Well, that's a big number.

Dr. WRANGHAM: That is not a huge surplus(ph).

RAEBURN: That's a surprise.

Let me stop for just a minute to remind people I'm Paul Raeburn. This is SCIENCE FRIDAY from NPR News.

And I think there're so many questions here. We've now - now, we've gone from anthropology into potential diet advice here, I think. Let me…

Dr. WRANGHAM: Well, yes. I mean…

(Soundbite of laughter)

Dr. WRANGHAM: …it's a great way to lose weight for people…

RAEBURN: Yeah. Yeah.

Dr. WRANGHAM: …to eat raw food.

RAEBURN: If you're not trying to evolve into a human. Let me take a call. We have Dan, from Boston. Go ahead, Dan.

DAN (Caller): Hi, gentlemen. I have a question about - well, I guess it's already been addressed to some degree, but exactly how the food is changed when it's cooked, from a molecular standpoint. I was just curious if you could - you can address that a little bit.

Dr. WRANGHAM: Well, yes. No, because I was only really getting into that. So what I was talking about was when you cook the food, then you increase the digestibility of many foods, many nutrients. But exactly how does that happen?

Well, we were talking about protein just then. And the conclusion of the people who investigated this question is that the significant consequence is that when you heat protein at all, then it tends to lose its structure. It's called denaturation, the sort of - it's like a ball of wool that is tightly wound. And as you heat the protein, it opens up. And the significance of being opened up is that it is then much easier for the digestive enzymes to come in and snip off the peptide bonds, to break off the amino acids.

RAEBURN: It's easier to digest, in other words. It's just easier to digest. Yeah.

Dr. WRANGHAM: Exactly. It becomes digestible in a way that it previously was not. And so this is a completely predictable consequence of heating. I mean, denaturation, of course, it's hugely important. One of the ways in which we denature protein is by putting them in acid. And guess what our stomach is full of? It's full of, you know, hydrochloric acid, pH 1 or 2 - very, very acidic. So that starts the process. But cooking really accelerates the amount of denaturation that happens and, therefore, it exposes these molecules to easy action of the digestive enzyme.

And another example is starch. Starch, when eaten raw, is a sort of semi-crystalline molecule, granule. And when it is cooked - properly, at least - then it opens up and the amylose and amylopectin - these critical sugars - these chains of sugars are opened up, and again, can be snipped off. So heat exposes the molecules to action by digestive enzymes.

RAEBURN: So this is - this, to me, is from a - again, pardon me for shifting the focus. But from a dietary direction, aside from the anthropological implications, we've - I mean, I have argued many times with many people about the fact that food has so many calories, that's it. And now you're saying that it's not a question of, you know - a carrot has some calories when it's cooked and some when it's raw.

Before you answer, however, we have to take a short break. We have lots more with Richard Wrangham. Please stay with us.

(Soundbite of music)

RAEBURN: This is SCIENCE FRIDAY from NPR News.

(Soundbite of music)

RAEBURN: From NPR News, this is SCIENCE FRIDAY. I'm Paul Raeburn.

We're talking this hour about how cooking made us human. My guest is Richard Wrangham, the author of "Catching Fire: How Cooking Made Us Human," oddly enough. He's also director of the Kibale Chimpanzee Project in Uganda and professor at Harvard University in Cambridge.

Now, before the break, Professor Wrangham, I was asking you about how many calories in a cooked carrot or a raw carrot. You mean to tell me that all those books I have that tell me how many calories are in this or that, they don't say anything about whether the food is cooked or raw. So what's going on? Do I have to throw those all away?

Dr. WRANGHAM: Well, I mean, we do have to modify it, and it's true for the food labeling system. Because if you look up on the USDA Web site and see how much - how many calories there are in a piece of raw meat or a piece of cooked meat or a raw potato or a cooked potato, you will find that old wisdom there, that it's the same. But look, when you cook, when you process the food, it really does affect the number of calories you get into your body. And there was a wonderful little experiment on rats that just shows this so clearly, and it's a very, very simple form of processing. It's a little analogous to cooking.

This is an experiment in which rats were given their regular chow pellets in two different forms. One was the ordinary pellet, and the other was with air added. They were puffed up. It's as if you took a grain of wheat and then puffed it off into puffed wheat.

RAEBURN: No nutrients added or subtracted, just air.

Dr. WRANGHAM: That's the only thing, air. And the experimenters were very careful. They gave exactly the same number of calories as measured - you know, the same weight of food to two groups of rats. And they measured how much locomotion they expended, and it was the same. So, same number of calories, same locomotor expenditure - you'd think that they would grow at the same rates. But the ones that ate the softer food grew faster, ended up heavier and had 30 percent more body fat.

RAEBURN: It can't be true.

Dr. WRANGHAM: So they grew obese.

RAEBURN: It can't be.

(Soundbite of laughter)

RAEBURN: It can't be true.

(Soundbite of laughter)

Dr. WRANGHAM: Well, you see, this is where the costs of digestion come in. It's so important, because they could actually show where the difference was. And the difference is this: that after a meal, the rats that ate the softer food had a lower rise in body temperature than those that ate the harder food. Their metabolic rate was lower because their bodies were working less hard, because there was less to do. They didn't have to soften their food.

And this is a wonderful little model, I think, for all sorts of examples in the human case. When we turn our beef into ground beef - just like hunters and gatherers who cook their meat and then pound it, what we're doing is making it easier for our bodies to digest the food and therefore sparing our bodies the need to waste energy, calories, on digesting the food. And the result is that the net caloric gain is greater when we eat food that has been more highly processed.

RAEBURN: Let me…

Dr. WRANGHAM: And, of course, this is fantastically significant in terms of the fact that we've got an obesity crisis and very highly processed food in the middle(ph).

RAEBURN: It's amazing. Let me - I know there are some listeners who want to get a crack at this. Let me try Katie in Cape Cod.

Hi, Katie.

KATIE (Caller): Hi. How are you?

RAEBURN: Good. Go ahead and ask your question.

KATIE: I've recently been introduced to the raw food diet, and I was wondering what you think about that and if you think it's all a hoax.

RAEBURN: Go ahead, doctor(ph).

Dr. WRANGHAM: Well, thanks, Katie.

RAEBURN: Go ahead.

Dr. WRANGHAM: I mean, that's a great question. And I think that it - the funny thing about the raw food diet is that many of the proponents argue that it is the natural thing to do. And I'm quite sure that it's not the natural thing to do in the sense that we're not biologically adapted for it, because if you look at raw foodists nowadays, they lose weight on a raw food diet, even to the point where women, in the only large survey that is being done of this, turn out to stop menstruating in half the cases when they are on a 100 percent raw food diet, an indication of how little energy they have. The scientists conclude that raw food diets lead to chronic energy shortage.

So if you want to gain energy, if you're living in the Third World, like a third of the people in the world, very hungry, then you - the last thing you want is a raw diet. But in our society, a raw diet can have all sorts of advantages. It can help you control your weight, and it has other advantages, too, for some people. I mean, there's lots of benefits that people report.

Some people find that they get reductions in rheumatoid arthritis, for instance, some very specific things like that. But many people feel a greater sense of well being, more vitality - quite often, less pain. And I think partly, this is going to be due to just eating less, and partly it probably is due to the fact that some people may be allergic or have some kind of response to the chemicals that are produced in cooked food. So, it's a very personal thing. You know, for some people, raw diets can be terrific. It's just that, you know, don't think they're natural, they're not.

RAEBURN: Are you on a raw diet, Katie?

KATIE: I am not on a raw diet, but I've started to eat a lot more raw foods, and I found that I did lose a good amount of weight by changing my diet.

RAEBURN: And now you know why. Thanks for calling.

KATIE: Thank you.

RAEBURN: We have another call from - let me see if I can get the right button here - from Mark in Saint Paul, Minnesota.

MARK (Caller): (unintelligible) and I think - thanks for taking my call.

RAEBURN: Where are you from?

MARK: South St. Paul.

RAEBURN: South Saint Paul. Okay I…

MARK: It's one of the misnomers. We're sort of south, but we have west, that's actually just west of South St. Paul. North is actually east of St. Paul, and (unintelligible) just like that.

RAEBURN: Wow. I'm with you. Go ahead with your question.

(Soundbite of laughter)

MARK: Well, I have actually two. I developed the second one while listening to you. The first one is about - well, not to be over about it, but aspect of race. Explain real quick. Scientific American did a piece where they showed some Pima Indians in Southwestern United States, that's - are the typical American diet: lots of meat, starch and so forth. They had overweight, diabetes, hypertension - the works.

But they had some (unintelligible) cousins. They were down in Southern Mexico that were having the traditional diet. They did not have any of the medical troubles. If there is such a problem in that where we, sort of, racially evolved, you might say, who - a measure where we can eat certain foods better than others.

RAEBURN: Okay, let's give that question to Richard Wrangham. And then, if we have time, we'll come back for your next one.

MARK: Okay, thank you.

Dr. WRANGHAM: Yeah. Well, thanks, Mark. And these are important questions, but I'm working at the level of the species differences, of what makes us different from chimpanzees. And I have not seen any evidence of - specifically, cooking - having different impacts or leading to different kinds of digestibilities among different peoples.

So, it certainly is the case that different peoples have some different enzymes. The famous one is the lactose digestion enzyme which is persistent in people who have got an evolutionary history of eating milk. And whether or not this applies to some of the products of cooked food, I can't tell you.

RAEBURN: Okay, Mark, give us the second question very quickly if you could, please.

MARK: Okay. It's about carmelization. Some researchers saying that carmelization can actually induce aging in certain measures. The question, basically, is: Do some - how does overcooking or undercooking affect foods can actually affect our aging? And in some regards to that, does aging affect our ability to eat certain foods? Thank you.

RAEBURN: Thanks, Mark.

Dr. WRANGHAM: Well, let me answer that question by saying that cooking does increase the concentration, very greatly, of a series of compounds called sometimes Maillard compound after the French biochemist discovered them, that are combinations of amino acids and sugars. And these are very much implicated in certain aspects of aging. We produce them more as we age, but the dietary source of them in cooking is a very high concentration compared to our normal production. And they're significant because they do produce tumors in rats. So, it is feared that they may be important in humans.

Now, recently, it was discovered that there was one of these acrylamide at unsuspectedly high concentrations in potato products, cooked potato products, and no one's known quite what to do with that. So, because as I understand it, the expectation was that this should've led to lots of cancers from people eating cooked potatoes, but actually it doesn't.

So maybe we have, as a species, adapted to the negative effects of these Maillard compounds. It's one of many, many areas where there's not enough information for us to be certain. But you're absolutely right that cooking produces these Maillard compounds, and many of them are known to be toxic in other animals, so there are cases where we want to know more about that.

RAEBURN: I'm sorry to say, we're out of time. I just have one final question for you. Have you thought of leaving Harvard and opening a restaurant?

(Soundbite of laughter)

Dr. WRANGHAM: Well, you know, there's a lot to be said for an evolutionary approach to eating, undoubtedly. And I'll take that suggestion on hold.

RAEBURN: Yeah, think it over. Our guest has been Richard Wrangham, the author of "Catching Fire: How Cooking Made Us Human." He's also a director of the Kibale Chimpanzee Project in Uganda, and Ruth Moore professor of biological anthropology and curator of primate behavioral biology at Harvard University in Cambridge, Massachusetts. Whether you open a restaurant or not, thanks for being with us.

Dr. WRANGHAM: Thanks a lot.

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Catching Fire

How Cooking Made Us Human

by Richard W. Wrangham

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