The impact of fire

Could the discovery of fire have been the cause of man's big brain?
08 November 2016

Interview with 

Professor Richard Wrangham, Harvard University


A fire burning


If the Jungle Book is anything to go by, man's mastery of fire is what truly sets us apart from our ape cousins but just how integral was the role of fire in making us what we are today? According to Harvard University's Richard Wrangham, it was vital. Connie Orbach heard how...

Richard - The cooking hypothesis is the hypothesis that the way that humans stopped being, basically, just another kind of great ape all had to do with our control of fire. The idea is that somewhere around 2 million years ago, pre-humans got sufficiently good at controlling fire that they came to rely on it completely. A major effect was to give us more energy. Another effect was to give us the body shape that we have today. Another one was to reduce the amount of time that we had to spend chewing and a major effect was to give us, ultimately, our big brains. And that's why the control of fire made us human.

Connie - Why would this change in body shape and more energy lead to a big brain?

Richard -   The brain comes from a supply of energy that is exceptionally large in humans compared to any other species. So our basal metabolic rate when we're just lying around doing nothing (sleeping), we're sending something between 20 and 25 percent of all the calories we use into the brain. No other animal can afford that, and we could not afford it if we were eating raw food and there are two reasons for that.

One is that we would spend so much time chewing our food that we would not be able to do anything else. It's been calculated that we would be spending something like ten hours a day just chewing in order to be able to get enough raw food to supply our brain. And the other reason is that, in humans, the one part of our body that is really outstandingly small compared to other primates, such as great apes, is our gut system. Our intestines are reduced in size by something like 30 percent compared to a great ape, and that saves us energy, and that energy can be diverted to go to the brain. Cooking makes our food so much more digestible that we can afford to have a smaller gut than we would have if we were a great ape.

Connie - This hypothesis - it certainly is very compelling. I find it incredibly interesting but it;s not been accepted by everyone has it? What are the problems with it?

Richard - Well, the big problem is a single one, which is that we don't have direct evidence of the control of fire going back to the time whenever it turns out that Homo erectus really did emerge. And the problem, of course, is that fire is something that is not easily evidenced in the fossil of the archeological record. So we have very good evidence of the control of fire in the last quarter of a million years; by the time you get to three quarter of a million years it's only just a handful of sites and then at 1 million years ago there's literally one site in Wonderwerk in South Africa. And after that, between 1 and 2 million years ago, you have maybe a dozen sites where people have said "we think that we can see evidence for the control of fire here, but we're not absolutely certain." And so it will be wonderful to look forward to the time when people are able to use techniques of higher resolution to be able to look in that period.

Connie - Could there have been another solution other than fire, for example, pummeling food, cutting it very finely, something like that ?

Richard - Yeah. Pounding food is a really interesting idea as an alternative to cooking, but even with electrical blending of foods it is impossible to get enough energy to satisfy the energy demands.

There was one particular study of several hundred German raw foodists led by Corinna Koebnick, and what she did was to assess the degree to which women's ovulatory cycle - their menstrual cycle - continued to operate. And what she found was that by the time women were eating 100 percent of their food raw, 50 percent of the women were amenorrheic that meant they weren't menstruating at all so, obviously, they weren't menstruating and couldn't have a baby.

So, somewhere in the human body frame, as we know it now, cannot survive on raw food in the wild because even in urban conditions where the food is providing lots of energy, it's being blended, people aren't taking much exercise, and they're getting food all year from supermarkets, nevertheless the average woman is unable to have a baby.

Connie - How are we going to come to a conclusion about this hypothesis one way or the other?

Richard - Yeah, we still don't know what's going to happen. You know, we don't have a clear plan for assessing the evidence for fire in the distant past. I know of places where people are looking at ancient sites and are feeling encouraged by what they are seeing. In the year since my book was published there have been several sites that were older than any previously known, so I assume that we will eventually them. But different sites produce different types of technical hazards and so there isn't going to be one single approach.

I was very struck by the fact that the site at Wonderwerk in South Africa, I think it's the only extant cave with a living floor that has been looked at. And, low and behold, it's 1 million years old, they find evidence of fire there - the only one in Africa. What they did was to show that inside the cave, somewhere at 30 metres deep, there was ash at the 1 million year level indicating that there was a consistent  reintroduction of flammable material into the cave, and on-one can think of any way that that could have happened unless people had been bringing the fuel in. So that's an example of an unusual kind of situation, and what we have to just hope for is the discovery of more unusual situations which will be able to test the fire hypothesis directly.

Chris - Harvard University's Richard Wrangham. Seem feasible to you Lee?

Lee - In part, I think it's obvious that the controlled use of fire, the cooking of meat would have had tremendous impact upon any hominids which happened to do it, whether they were direct ancestor of humans or others.  I think the more controversial part of to sort of summarise that is -  is that event associated with the encephalisation, increasing brain size?

Chris - Because it's associated in time but we can't say one caused the other?

Lee - We think it's associated in time and I think Richard was doing a good point of  talking about the lack of evidence. Very similar to the lack of association between hominids species in archeology. I guess a falsification of that hypothesis would be if we happen to find a very small-brained hominid that was using fire and wasn't undergoing that sort of enchephalisation. But he is right, these caves, the exploration needs to be done. It is probably going to be in a cave where we find these sort of direct associations and I think there's a real possibilities of breakthroughs in testing these hypotheses in the future.

Chris - Matthew - are fire remains easy to find and is there any other proxy marker we could use for this?

Matthew - Well listening to Richard, one is brought to mind of the fact that we do have this growth on teeth dental plaque - dental calculus. And what we have found in Neanderthals is evidence of particulate material, ash from fire. So if, it's a long shot, but there was calculus in some of this material and we could find evidence of burning trapped in the calculus - that would be a direct line of evidence.

Chris - Very nice. Thank you very much Matthew. 


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