Catching Fire. The other one.

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Catching Fire is apparently a very popular book and/or movie that everyone is very excited about. But Catching Fire: How Cooking Made Us Human is a different a book about some interesting research I was involved in about the origin of our genus, Homo.

You can pick up a copy of our paper on this page. We call it “The Cooking Hypothesis.” The basic idea can be summarized with these points:

1) Cooking food transformed human ecology. Many potential foods in the environment can’t be consumed by humans (or apes in general) without cooking. But adding cooking to our species-specific technology, we can access those foods effectively transforming our ecology to a much greater extent than the vast majority of evolutionary transitions, especially single-event transitions, have ever done. The total number of calories in the natural environment that become available to an ape that can cook goes up by orders of magnitude.

2) This increase in available calories left a biological signal that is very impressive. Two major changes happened in the hominid body (in early Homo erecuts/ergaster). One is an approximate doubling in body size from an earlier Australopithecine or “Early Homo” ancestor. The other is a reduction in tooth size. Less eating equipment with a body demanding so much more in energy to grow and maintain signals a fundamental change in the food supply. There may be more than one way this could have happened, but so far adding cooking to our technology seems to be the best explanation.

3) Related, this is when we see brain size, relative to body size and in absolute terms, increase. Neural tissue is picky, expensive, and costly. Having a significant increase in brain size may be related to the demands (on the brain) of adding cooking to our behavior in that the size increase is allowed by the extra energy. And, it may be related in that the larger brain may provide the capacity to have this behavior.

4) The actual act of cooking, as a technology, may or may not demand a larger brain. But the process of cooking almost certainly involves central place foraging (bringing all the food back to one place, much of the time, to cook it) and delayed consumption (as opposed to eating the food where you find it). The basic pattern for a chimpanzee-like ancestor is to eat the food where you find it. Bringing food into close proximity to other members of your group virtually guarantees direct competition for food, which makes getting to food to begin with a highly questionable thing to do. In order for cooking to work, the social interactions typical of an ape have to be modified significantly. Cooking demanded, facilitated, and made major changes in social structure “worth it” from the point of view of natural selection.

5) These changes in social structure are probably indicated as well by changes in stone tool technology. Early cookers also were early hand-ax makers, for example. Human ancestors went from making primarily expedient, one time use, very simple stone tools to making tools that required a great deal of investment in time and energy to learn the technology, get good at it, and even for the production of individual tools (including acquisition of better than average raw materials in many cases). Once the tools were made they seem to have been used, often, for long periods of time. It is hard to imagine a chimp-like creature carrying around a tool into which she invested time and energy without it being taken away. This is an important transformation.

6) Less visible but very likely is a change in social system which could be called the rise of proto marriage. Sexual arrangements of a human-like kind are very different than for chimp. The ability to allow others to possess food or invest in more sophisticated technologies may be parallel to the ability to have more or less exclusive sexual contracts among individuals. This is indicated independently in the fossil record by a large decrease in sexual dimorphism in body size. In polygynous species like chimps males are often much larger than females, and this seems to have been the case with pre-Homo erectus/ergaster ancestors. But at the same time the body size increase and tooth size decrease happen, we also see a reduction in sexual dimorphism in body size, strongly indicating a major change in social arrangements. The best two explanations for this may be a shift to a gibbon-like pattern of paired-off monogamous adults living more or less alone, or a human-like pattern of paired-off monogamous adults living in larger social groups.

It is an idea that would have caught on. It would have selected for more nuanced communication, and may thus have facilitated the origin of what we now know of as human language and symbolic processing.

So when you are eating your Thanksgiving dinner this year, most of which will be cooked, look around at the people at the table and, briefly, imagine them to be chimps. Then go back to your meal and try to put all those thoughts aside…

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24 thoughts on “Catching Fire. The other one.

  1. I read and recommended the book several years ago. Since then a bout of oral cancer , loss of dentition due to radiation therapy, and a years-long regime of liquids have led to even more appreciation of diet technology. Ownership of a Vita-mix is a far cry from the needs of my ancient ancestors. Of course by now, at 71, I’ve already lived to an age that would have been unthinkable millennia ago, but that has not diminished my appreciation and gratitude for the creativity of the Old Ones.

  2. Greg, Lars Werdelin has an article in the latest Scientific American about the timing of large carnivore extinction in Africa (actually, more precisely, a pronounced and permanent drop in species diversity) and the apparent adoption of hunting by hominids. Does this fit with the proposed timing of the advent of cooking?

  3. The total number of calories in the natural environment that become available to an ape that can cook goes up by orders of magnitude.

    Miscellaneous tangents:

    * “Cooking” when first invented involved either dropping something into fire/coals or skewering it with a stick to pass it over/through flames, no? Works great for bigger pieces of meat, not so much for gathered seeds, leaves, roots, grubs, eggs, small animals…

    * Cooking-quality pottery must have taken generations of acute r&d frustration. The payoff to a gathering economy from being able to make a soup of readily scrounged edibles must have been revolutionary.

    * Anywhere with a lot of tubers, the baked-in-mud technique would likely be discovered not long after the invention of campfires. No doubt Africa has at least its share of tubers, but that benefit could only occur after fire-using was established.

    * How much advantage would keeping a nice bright fire going at night add up to in terms of predation prevention? Or a nice smoky fire as insect deterrent?

    * How much benefit came from cooking as a calorie catalyst as compared to parasite prevention?

    * Field observations suggest tendencies to gather around and stare at fires has been strongly selected for during multiple generations of Homo (semi)sapiens.

  4. I didn’t mention it in this post but we postulated based on earlier work that tubers and roots etc would be among the first things cooked. Seeds, eggs, etc. don’t need to be cooked. Small animals are easily cooked on a fire with no extra instruments.. I’ve eaten plenty of small rodents, song birds, and bats cooked that way.

    (On the same page I pointed to you can see research on tubers that relates.)

    Fires don’t scare away predators in my experience. At all. Archaeologists have long suggested that this is a role of fire but this is wishful thinking. As a calorie catalist fire has potential (see the Wrangham et all paper).

    Lars: I’ll have to look at that timing.

  5. Cooking also kills bacteria and other food-borne infectious agents and parasites. Disposal of food wastes in fire, such as by throwing the inedible (to humans) parts of food plants and animals into a fire, also renders them unsuitable for use by flies and rodents.

    These factors would have produced changes in disease and mortality patterns over time. Are there any archaeological data on that?

  6. It also occurs to me that the advent of fire would have led to the at-first accidental burning of plants that happened to be poisonous or psychoactive. This would have had to produce the impression that an “unseen force” was striking people dead, making them sick, or giving them visions: an unseen force entirely different to that unleashed by eating the respective plants.

    The question is, would early humans have attributed the new “unseen force” primarily to the fire, the smoke, or the plants? And how would that have affected the development of “religious” beliefs early in human history? (Even to this day, the use of incense in churches can be considered a faint echo of the idea that there is a connection between smoke and the deity or spiritual realm.)

  7. Interesting. If purposefully made fire use was a feature of H. ercectus or ergaster, that means that H. sapiens may have been literally eating cooked food for as long as we were a species. So much for the claims of raw food enthusiasts that we were evolutionary adapted to eating raw food (not that I put much stock in those types of arguments in the first place).

    Also, regarding your (Greg H) comment that fire does not deter predators: since it seems to be an article of faith (or at least a scientific “urban legend”) that it does, how do you think this belief has persisted so long?

    BTW, when you wrote you’ve eaten “bats” cooked on a fire I almost read that as “brats,” and thought “big deal.” ;-D


  8. Nick: Yes, exactly.

    How has the belief of fire working on predators persisted? It is one of those made up things, made up by arm chair theorists, who never tested it! I assumed it was likely true until the first time I tried to scare off a predator with fire, and that was the first of a series of failed attempts to do to.

    Predators probably avoid human hunters because the penalty of harassing them is severe and extend to kin. But fire per say is only a signal that there may be something to eat.

  9. @Pierce Butler: I’ve cooked all kinds of veggies on sticks over a fire. My friends and I do “everything on a stick” parties, where we build a fire and cook wildly creative food on sticks. The bacon rolls are a particular hit, although I don’t think Neanderthals had those. And the whole quail were easy and delicious.

    Cooking roots in coals is easy and works great, especially if you wrap them first (aluminum foil or large green leaves). Eggs can be cooked either over the fire with tongs (fast, but there’s some risk of explosion) or placed in a mildly hot spot near the coals for an hour or so.

    Probably the best thing I’ve tasted from a campfire was the whole chicken, wrapped up and buried in coals under the fire, like they do with pigs in the South Pacific.

    Cooking food together is about as human as you can get, and I think it’s pretty unlikely our fully human ancestors ever lived any other way.

  10. The Efe Pygmies typically cook using pots that are either traditional clay ones they are theoretically able to make or, more commonly, cheap aluminum trade pots that are used in the region.

    One day I asked a group I was living with if they could cook without the pots. I expected them to say yes, but to do things like those suggested here, using sticks for certain things, or putting objects on the coals, etc. Also, I expected them to limit the range of things they would be willing to cook this way.

    What happened was instead quite shocking and turned out to be an example of how limited we are in making guesses as to what is possible or not possible, or even difficult vs. easy.

    They told me that occasionally they needed to cook without pots, so they had a way to do this.

    They made rice, beans, and cooked some meat. They did it all just as you would do it with pots, but they made “pots” out of leaves. It wall went very well and they made it look easy.

  11. I think there is a typo in #6:
    “…at the same time the body size increase and tooth size increase happen”. Shouln’t that be ‘tooth size decrease”?

    Fascinating hypothesis. Are there implications in this view for possibly finding earlier direct evidence of fire use so early – 1.8 MYA is a lot earlier than the current evidence, isn’t it?

  12. Good catch, thanks.

    As for the earliest evidence of fire, we are arguing that the body size increase IS a biological signal for that, but I know that is indirect.

    The earliest evidence for fire is the burned patches at East Turkana at 1.5 mya. Not every one accepts that, but on the other hand, many who reject that evidence accept Zhoukoudian at 0.6 mya even though we think that is guano burning naturally. But since it is a later date and longer in the literature it is somehow less uncomfortable calling burning sloth shit human hominid controlled fire than patches that look like fire hearths and have magnetic properties consistent with controlled fire direct evidence.

    There is also evidence in South Africa over a million.

  13. Just a quick note in response to the commonly made misstatement way up in comment #1 that
    Of course by now, at 71, I’ve already lived to an age that would have been unthinkable millennia ago
    70-80 was the typical life expectancy (if you survived childhood) three thousand years ago. This is clearly stated in Psalms 90:10 (a historical note, not a supernatural one).

  14. Fires don’t scare away predators in my experience.

    A former national park warden in South Africa/Southwest Africa (as it was then) told me that one evening he returned to the camp fire he’d left blazing to deter predators, only to find it surrounded by 5 lions basking in the warmth. A Namibian colleague related that, as a student, one evening she stayed alone at a campsite. A rhino dashed in from the dark then stamped around, dispersing and putting out the fire before leaving.

    Apart from using metal or earthenware cooking pots, mopani worms (caterpillars) are cooking by dropping them in glowing embers. It seems the ash also has a preservative function. I’ve read that in some societies, food is cooked by dropping fire-heated rocks into gourds containing water (and the food).

  15. @Greg #14:
    Thank you for those extra data points.
    I’ll get the book and start following the paths on that fire controlling evidence. I agree that there should be a good (very good) reason or reasons for these roughly contemporary phenontypical shifts in body size, tooth shrinking, and brain growth, etc. That there _is_ >1MYA evidence albeit not fully recognized is great to know. Now to search it out!

  16. Richard: Your comment came through just as I was about to give a lecture on early fire and I worked in your examples.

    The idea that Rhinos stomp out fires is a meme I’ve heard before, and it is part of “The Gods Must Be Crazy” … still not sure if I believe it but I’ve heard stranger things (in South Africa!)

  17. Greg: I mentioned ‘The Gods Must Be Crazy’ to the colleague who told me about the rhino stamping out the fire – she had not seen the film and I don’t think she was one to exaggerate, so I’m inclined to believe her.

  18. What about the idea that cooking food pre-digests it so that energy used for the gut is made available for the brain?

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