Gene Expression


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A few weeks ago I commented on Richard Wrangham’s discussion with Robert Wright. Though most of the conversation was given over to the arguments in Wrangham’s latest book Catching Fire: How Cooking Made Us Human, I focused on the older Demonic Males: Apes and the Origins of Human Violence. One of the main reasons is that the latter was a book I had read. A few days ago I managed to get through Catching Fire. Though the content wasn’t particularly surprising or novel, Wrangham has been articulating the general model for years, the details were of interest and at ~200 pages it was a quick read. In some ways it resembles typical X-Made-Man books, such as Robin Dunbar’s Grooming, Gossip, and the Evolution of Language, and so can get tiresome. Rather than focusing language, or human sociality, tool use, or the consumption of meat, Wrangham naturally draws everything back into the use of fire and cooking. Despite this the argument is so heavily larded with specific detail that even if you find the emphasis on the overall thesis a bit heavy-handed it’s worth a read. Obviously publishers would be less than excited by a book titled “How cooking, language, tools and bipedality made us human,” but I think some of these other factors are left implicit in the text.

Catching Fire‘s basic thesis is interlaced throughout the narrative, but there’s a definite disciplinary progression. Naturally Wrangham starts with basic chemisty, physiology and anatomy. Contemporary experiments and observations loom large. It may not be On Food and Cooking: The Science and Lore of the Kitchen, but it comes close at moments. Then he proceeds to paleoanthropology and other assorted historical sciences. Finally he gets to the soft meaty heart of the implications of his thesis for us moderns, surveying the treacherous terrain of ethnography and cultural anthropology. There’s also an epilogue which seems to be tacked on for some public policy relevance, and has somewhat the feel of Michael Pollan’s latest book.

The first few chapters which focus on chemistry and physiology are the most interesting for low-level datavores. A clear and compelling case is made that cooking food makes it so that an organism can extract the maximum amount of energy per unit. I was interested to find out that Claude Lévi-Strauss argued that human taming of fire was critical for psyhcological reasons, in particular setting us apart from beasts. That is, there were no material consequences of human control of fire, something which might surprise anyone who knows the plot of The Jungle Book. Wrangham presents some paleontological data in regards to fire use which dates to nearly 1 million years in the past, which supports his contention that the control of fire and the emergence of cooking likely was a feature of Homo erectus. There are other circumstanial pieces of information which buttress this contention. To me the most persuasive one was the likelihood that Homo erectus slept on the ground because of their full bipedality, and the only plausible way they could defend themselves against predation by large animals would be a communal fire. Additionally apparently there are other clear signs of dental and digestive changes in erectus which suggests a sort of “great leap forward” vis-a-vis Homo habilus. I do not know much about paleoanthropology when it come to fossils, but this is something that I have found to be generally true. Homo erectus was a large and efficient bipedal machine, when it comes to goings on below the neck our own species has only changed marginally. Though our cranial capacities have increased in the past few million years, Homo erectus was likely qualitatively different from habilus in this regard. The former was more a man and the latter was more an ape.

Of course there’s another model for changes in terms of consumption that explains the erectine leap forward, that our lineage shifted from being a predominantly vegetarian one as are all primates, to a meat eating one. The arguments are laid out in books such as The Hunting Apes: Meat Eating and the Origins of Human Behavior. Many of the physiological and anatomical details which suggest a shift to cooking have also been argued for a shift to meat, so Wrangham must review both models and make a case for why cooking is superior to simply meat. First, the case for why there was likely some sort of dietary shift. Humans, for our size, have small guts, small teeth, small jaws, etc. We’re simply not very adept at consuming large quantities of low quality food, as is evident when starving human populations make recourse to grass, bark, and such. Our cousins the gorillas, and to a lesser extent the chimps, are. The small gut is a critical point, because it is metabolically an expensive organ. The digestive system has to use energy to generate energy. Another organ which is expensive is our brain, which utilizes about 20% of our body’s metabolism, as opposed to 10% for a typical mammal.

How can we get the math to work out? Consume food which is much more energetically rich, and which is easier to process. Meat would seem to fall into this category, and true enough carnivores have much smaller digestive systems, and often relatively large brains compared to herbivores. Bu there are differences between the digestive processes of conventional carnivores and humans which imply that the analogy is imperfect. A look at human teeth makes it clear we’re not specialized in the same way cats or dogs are, and our stomaches do not seem to break down meat through physical action as in these carnivores. Meat may be rich in energy, but it is still relatively tough, and increasing surface area for digestive acids to work is critical. Humans do eat raw meat, but they are selective, preferring extremely soft and tender tissue, or meat which has been processed in some manner (e.g., burger patties). Reprocessing meat physically requires time and energy. Wrangham observes that this is one reason that chimps are opportunistic in their hunting, they simply don’t get as much out of it as they otherwise would because of the difficulties of tearing into and consuming raw muscle.

But how much of an energetic difference does this make? Through experiments which track the metabolism of various organisms it is reported that shredding meat increases net energy extraction by 12.5%, and cooking it increases it by 12.5%, and the two are additive so shredded and cooked meat may impart 1/4 more calories per unit than raw unprocessed meat. This is an enormous difference. This is probably a low bound estimate because the methods used did not seem to account well for how much energy shredding and processing would take, as well as the opportunity cost of these activities. The combination of cutting with tools and cooking seem like a sure fire way to increase the amount of calories per unit, and reduce the energy expended in preprocessing. Additionally, both cooking and shredding are important for vegetable matters. In extant small-scale hunter-gatherer societies there is a wide range of proportion of calories obtained from meat and vegetables, and the range is constrained by ecology and not human preference. The fact that humans can live on predominantly meat and vegetable diets, combined with our generalist dentition, suggests that an emphasis on the processing of food in addition to its form is the correct. We simply aren’t as constricted as pandas or cats.

Surprisingly most organisms also preferred foods cooked to non-cooked. This seems peculiar as humans are the only organisms who consume food cooked on a regular basis. What gives here? There are general differences between cooked and uncooked foods, and most species have an innate ability to discern when their food is more palatable. Similarly, though most of the fruits that chimpanzees in the wild consume are rather lacking in sweetness, they habituate themselves naturally to the much sweeter fruits which humans provide them. Their preferences are general and extend naturally to novel fruits and vegetables. As a point of possible future research Wrangham observes that cooking tends to generate chemical byproducts, some of which are known to be carcinogenic, and it is therefore likely that we have developed adaptations to battle the negative effects of cooking. There isn’t much exploration of possibilities, but it seems likely that biochemists and geneticists may be able to elucidate the mechanisms which distinguish us from our relatives in this dimension.

Obviously 1/4 more calories per unit has an adaptive significance. Aside from the anatomical and behavioral changes this might entail, there is an obvious natural experiment which might test what happens when humans shift away from cooked food. The “raw food” movement. Raw foodists tend to be thin. The reason behind this is simple: they gain fewer calories per unit from the foods they consume, and generally the foods they consume are lower in calories to begin with even if cooked. It is important to note that modern raw food enthusiasts have access to a wide array of goods thanks to modern agriculture, and can supplement their diet in a manner impossible in a premodern period such as adding a great deal of oil to their diet. Some research suggests that 1/3 of the calories for some raw foodists derives from these oils. I’m not particularly interested in the nutritional consequences, rather, more relevant are reports that 1/2 of female raw foodists stop menstruating and many of the males claim reduced sexual appetite. Raw foodists are generally loony New Age types, and apparently many believe that menstruation and ejaculation are processes which evolved to expel toxins from their bodies, so their decrease of sexual function is an indicator that they are no longer ingesting toxins. But from an evolutionary perspective this is a very strong argument that the ancient human diet was likely to not be raw; if modern raw foodists who have access to a wide variety of items exhibit such low potential reproductive fitness it is certain that pre-modern populations on the Malthusian margin would be far more likely to simply go extinct. It seems that no matter what you an say for the positive thesis, these sorts of data go a long way toward eliminating the competing models from the set of the plausible.

Much of the second half of the book ranges over the implications of the high calorie and low energy processing requirements enabled by fire. By analogy, fire is a technology, and replaced human activity in terms of making food more palatable for our digestive system. Instead of chewing for 3 or 4 hours, we simply cook for a time and we can chew the food with relative ease. Similarly, steam replaced muscle power, and so made land shipment economically competitive with water transport for the first time in human history. This change had many consequences. In Catching Fire Richard Wrangham elaborates a theory for how cooking produced our normal sexual division of labor and more generally resulted in patriarchy in most small-scale societies. You may, or may not, believe it, and similar stories have been told about tools, or language, or the importance of meat acquisition. To some extent the cultural anthropologial inferences are interesting only once you accept the role of fire and cooking as a catalyst for human evolution, you may be able to construct plausible alternative explanations based on tool production and use. Unlike the earlier sections on the chemistry and physiology of food production, processing and consumption, the later chapters are difficult to unpack as they involve more detailed speculations which hinge upon many moving parts. Still fascinating, but in many ways less concrete and more “Just So.”

The last chapter jumps back to the beginning to some extent. A strong case is laid out that modern food labeling methodologies are imprecise, and may be resulting in the obesity epidemic we see around us. The research reported above strongly imply that the physical structure of food affects how much net caloric input we receive. Therefore, grains high in fiber tend to deliver fewer calories than extremely finely milled flour. To some extent this correlates with the glycemic index. The data here are numerous, and makes biological sense. I suspect few would quibble with the assertion in the abstract. Of course a 10-20% difference in calories between two food sources of the same substance of different higher order structures might be tolerable for “government work,” but the extra caloric intake may make a great deal of difference in terms of long term weight gain. Reducing or increasing intake 10-20% may have an enormous effect on the caloric margins. Modern industrial processed foods are extremely rich and efficient sources of calories per unit. In contrast, “whole foods” tend to be much less efficient because of their complex structure, and so are much more expensive per calorie unit. The reason raw foodists lose weight so quickly is that they eat “whole foods” necessarily because of their dietary constraints. Wrangham doesn’t engage in a jeremiad against the modern food industry, that isn’t his brief, rather, he is making a case that assays of calories should be reconsidered. Approximations which might justifiable in terms of basic science may have extremely significant public health impacts in the applied domain.

As with most science the “moral” of the story is for you to draw. Though I think I can infer the author’s general attitudes when it comes to processed foods there isn’t a wholesale assault upon them. After all one reason that processed foods are “bad” for us is that they “fit” with the capacities of our digestive system so well! Fire & cooking were simply the first steps in the long progression toward the industrialization of food processing. Similarly, the specialization enabled and enforced by cooking may simply be a precursor to the modern economy, where specialization results in gains of efficiency and productivity. There are critics who might claim that the specialization as gone too far.

Comments

  1. #1 David B
    June 21, 2009

    There is an interesting new(ish) book by Sarah Blaffer Hrdy, ‘Mothers and Others’, which argues that the main distinction of human evolution (compared to other great apes) was a shift away from childcare exclusively by the child’s mother (as in other apes) and towards childcare partly shared by other adults in the group. This created a selective environment favouring cooperation and reciprocity. I’m still reading it, but she makes a good case (so far).

  2. #2 daedalus2u
    June 21, 2009

    I completely agree about fire being essential for humans for cooking.

    I think the need for fire to protect against predators is overblown. Four adults, 3 with longish spears and the fourth throwing fist sized rocks could probably defend against any single predator. Six or eight could probably take a carcass from a group of predators. The spear holders protect the stone throwers. At point blank range, a fist sized stone will do considerable and unacceptable damage to a predator.

    Extant predators may have an instinctive fear of fire because fire was associated with humans who would take from them what ever the humans wanted to take, or kill them in the process.

  3. #3 Mike
    June 21, 2009

    The food labeling discussion makes me think of the common weather reporting ‘feels like’ temperature. 98 degrees — feels like 102 degrees.

    I’d like to see that on food labels. 100 cals.– feels like 88 cals.

  4. #4 razib
    June 21, 2009

    i didn’t think erectus had spears.

  5. #5 Colugo
    June 21, 2009

    Maybe aging/fermenting rather than cooking was the breakthrough that allowed more nutrients to be extracted from vegetation and meat.

  6. #6 Greg Laden
    June 21, 2009

    Nice review. I’m writing one as well, but as a co-author of the seminal paper leading to this book, I have a bias (in favor of the hypothesis).

    I’d like to underscore two things: Body size increase and change in habitat (allowed by novel foods not edible to primates until cooked).

    I won’t comment further, just mentioning them.

    Also, not mentioned by Wrangham and not generally known: Cooked foods may contain compounds that are actually very bad for some animals that don’t eat cooked foods, but that don’t seem to bother humans (much). Which is interesting.

  7. #7 agnostic
    June 21, 2009

    Does he talk mostly about muscle meat, or fat as well? You can’t eat more than about 30% of your calories as protein — the rest will be fat and carbs, mostly fat pre-agriculture. There’s still the advantage of extracting more energy and nutrients from that minority of food calories, but since the bulk of our diet wouldn’t have needed extensive processing (being fats), that takes away from the “great leap forward” or X-Made-Man interpretation.

    And some of that protein would have come from organ meat, which we used to eat extensively, and which isn’t nearly as tough as a shoulder cut steak.

    The loss of reproductive function among Raw Foodists — from what I sense, most of whom are specifically vegan or vegetarian (or mostly so) — is not due to fewer calories but to a lack of fat and especially cholesterol. Cholesterol is the precursor to all steroid hormones, including the estrogens and androgens (and vitamin D). 1200 calories of bacon and Gruyere cheese aren’t the same as 1200 calories of spinach and soybeans — on the first diet, you’re still down to fuck.

    Labels don’t have to do with obesity. Gary Taubes in his talks provides a useful way to see how trying to alter calories in / calories out cannot cause weight gain or loss over the long term:

    Assume a diet of 2700 cal / day (typical)
    So, 1 million cal / year, and 10 million cal / decade
    This is 12 tons of food / decade
    To keep weight within 10 lbs over this time, you need a calorie-counting accuracy to better than 0.4%, or 11 cal / day.

    No one, except the lab scientist who controls patients’ diets in a metabolic ward, can do that, so the implication is that we’d all end up obese (if too high) or emaciated (if too low) over our lifetimes. That doesn’t happen, so counting calories in / out cannot cause weight gain or loss.

    The reason is that the balance between energy in and out is regulated homeostatically by the body — that’s where the accuracy comes from, not from our conscious calculation from labels. It’s the same with any other important bodily function — air in and air out, heartbeats per minute, etc. Too important to trust to conscious action, so it’s regulated homeostatically by systems beyond our conscious control.

    I’m glad to hear there’s a bunch of data in the book, but his interpretations of it sound slightly off.

  8. #8 bioIgnoramus
    June 21, 2009

    In the Australian TV series “Bush tucker man” the point was made that the energy expended in opening shellfish could take up a large part of the energy generated by eating them. The BT man then showed the intelligent way to do it – he threw the mussels (or whatever they were) on the hot embers of a fire and the shells obligingly opened.

  9. #9 razib
    June 21, 2009

    he mentions protein poisoning. reports that wild game has extremely low fat content.

  10. #10 tom bri
    June 21, 2009

    “…A look at human teeth makes it clear we’re not specialized in the same way cats or dogs are, and our stomaches do not seem to break down meat through physical action as in these carnivores. Meat may be rich in energy, but it is still relatively tough, and increasing surface area for digestive acids to work is critical…

    I have to go with Agnostic on this one.

    Have you ever eaten raw muscle meat? Our front teeth are perfectly designed for nipping off small bits. Wrangham may be right about the caloric advantages for cooking plant foods but he is way out of there on meat.

    Cooked meat is cut into chunks and chewed with the back teeth. This is hard work for tough meat. Raw meat can be easily eaten with nothing more than the front teeth.

  11. #11 razib
    June 21, 2009

    tom, it depends on the type of meat. as i alluded to above. have you read my post?

  12. #12 agnostic
    June 21, 2009

    reports that wild game has extremely low fat content.

    Nah, as long as you stay away from Cape Buffalo, you’re good. Here’s a photo album from someone’s fieldwork with the Hadza, an H-G group in Eastern Africa:

    Hadza pics

    There are several pics of the meat they’re preparing, and it’s marbled enough that it’s visible from 10 feet away. Wild and grass-fed animals are leaner and tend to have less saturated fat than industrial meat, but it’s not “extremely lean.”

    And Wrangham has to recall that H-Gs — and even more modern societies, when times were good — ate animal organs too. Waste not, want not. Liver, kidney, brains, heart, testicles, tripe, tongue, you name it. Liver, tongue, and brains particularly are high in fat.

    We have a tendency to project what our camping trips are like back into the past — so, liver and brains are just completely out of sight and out of mind — but throughout most of history, this offal was prized.

    Another reason we know that pre-agricultural people didn’t consume so much protein is that they weren’t taking in lots of digestible carbs (not being agriculturalists who had potatoes, wheat, etc.), which leaves proteins and fats. If they were relying mostly on protein, they’d suffer from protein poisoning and probably would’ve had insulin-mediated diseases — dietary protein gets converted into glucose by the liver (gluconeogenesis).

    Usually not a problem, since protein also stimulates the release of glucagon, the “anti-insulin” hormone, but if you eat mostly protein and little fat, it’ll become noticeable. But insulin-related diseases — obesity, Type II diabetes, etc. — are unknown among those eating an H-G diet. So, they must have been relying mostly on fats.

  13. #13 doug l
    June 21, 2009

    Some very interesting thoughts. I’m hoping to get the book and read more about it.
    I do wonder about human dentition. There is one other animal that does have, at least to my eyes, somewhat similar teeth from the stanpoint of their aparent function: Sea Otters. I dont’ mean to presume anythin other than they look similar, and don’t presume to invoke anything about “aquatic apes” but there is an element of selective bias towards fossil bearing areas that are not coastal, it seems. A diet rich in shellfish seems to accompany a certain degree of fitness for humans who live on that kind of diet, and we don’t need tearing fangs or shearing carnasials for shellfish and finned fish in general, but more anvil shaped gnashers and shovel shaped biting incisors, and those sea otters certainly exhibit that.
    Anyhow, I’m not a science-pro or anything, but an avid reader on human origins and other natural history subjects and consequenty I’m shamelessly willing to imagine a human past that no doubt included the African savannah and steppes of Eurasia, but find it odd that our perspective is so terrestrial when anyone who’s ever been fortunate to live on a beach where the natural abundance is as profuse as it can be it just is an ideal habitat if the issue of exposure through fire and other tool-using technology, including shelter, is aculturated, while ingoring that a band of clever social apes who could use strategy and rocks and sharp pointed sticks, and fire, couldn’t have been at least as significant contributing to the evolution of our physical and physiological traits.
    Anyhow, always interesting material to ponder and thanks.
    I recommend you try a couple of weeks on the shores of New Zealand’s Able Tasman Park, eating mostly shellfish and the odd natural food, I seem to recall the quavas or fijoas or similar semi-tropical fruit that we grew to like, to supplement our supply of ramen and gorp, were prett good and I think we actually put on weight.

  14. #14 tom bri
    June 22, 2009

    Razib, sure I read the post, all of it. I stand by my comment. Human front teeth are ideal for cutting meat, just take a hunk in your hands and shear it off with sideways jerks. Very similar to the way a dog uses its shearing teeth on large hunks of meat. They jerk their heads sideways.

    Cooking toughens meat, unless you boil, steam or bake it a long time. Rare steak is easier to eat than well done, raw easiest of all.

    As for the ‘type of meat’ you mention, I would be interested to know which type is inedible raw. Modern hunter-gatherers live on the poverty-stricken ecological fringes. That certainly doesn’t represent the bulk of human history. Just as lions rarely starve unless there is general famine, ancient humans ate well most of the time. They could pick and choose what kinds of animals to eat and what parts of those animal, most of the time.

    I suspect that raw foodists lose so much weight because few of them eat enough fat, and plant foods mostly do need cooking to maximize efficient digestion.

  15. #15 Sandgroper
    June 22, 2009

    Zeeb – There is this: http://www.schoeningerspeere.de/ But I think that’s a bit of a red herring. All animals except Homo are afraid of fire, and it’s about the most effective defence against predators that there is, especially nocturnal ones. It’s also very useful for hunting.

    But I think that’s also a bit of a red herring. For me, Richard Wrangham tries just a bit too hard to sustain the connection between the need for meat preparation and division of labour. He doesn’t need to try that hard. I once read a very good account by Greg Laden of how a lot of tubers and roots need to be cooked to make them edible for humans. I hope I’m not pre-empting Greg by mentioning it.

    HGs do a lot of food preparation of vegetable matter as well as meat, as this photo kindly referenced by ArseMan illustrates: http://www.flickr.com/photos/briansgallery/346528665/in/set-72157594460801667/ And guess who gets to do most of the work?

    In some cases, Australian Aboriginal women put an amazing amount of effort into preparation of vegetable matter in order to render it edible – including some stuff that was toxic unless put through an extended and complex process. I’ve always wondered how the hell they figured it out.

    Why go to that much effort? Because it was a source of carbohydrates, which by weight provide double the calories of protein and fat, and as noted, HG diets are usually low in carbs, and also often low in fat, to the extent that the organs are often prized above the muscle meats, as Arseman has observed. A lot of game animals really are low fat, even compared to free range grass-fed domestics, which have been selectively bred for fat.

    So I do buy Richard Wrangham’s hypothesis. To get necessary nutritional balance as well as sufficient calorific value, division of labour to enable sufficient effort to be given to food preparation was a real advantage.

  16. #16 Gary Katch
    June 22, 2009

    “Raw foodists tend to be thin. The reason behind this is simple: they gain fewer calories per unit from the foods they consume…”

    So why don’t they just eat more units?

    The above quote is an example of the dogmatic “caloric balance” hypothesis of weight regulation, which is completely busted by Gary Taubes’ book Good Calories, Bad Calories.

  17. #17 agnostic
    June 22, 2009

    Because it was a source of carbohydrates, which by weight provide double the calories of protein and fat

    Other way around — protein and carbs provide 4 kcal/g and fat provides 9 kcal/g.

  18. #18 zayıflama
    June 22, 2009

    Extant predators may have an instinctive fear of fire because fire was associated with humans who would take from them what ever the humans wanted to take, or kill them in the process.

  19. #19 Sandgroper
    June 22, 2009

    Erm, right, wrong way round. But the point I was trying to get at is that Aboriginal people went to a lot of trouble to get carbs when they could, which was one of numerous things that required division of labour, not just hunting and preparation of meat.

  20. #20 Blind Squirrel FCD
    June 23, 2009

    i didn’t think erectus had spears.

    Yes they did.

    http://www.archaeology.org/9705/newsbriefs/spears.html

  21. #21 Emily
    June 23, 2009

    The Andaman Islanders had no fire-making skills.

  22. #22 toto
    June 23, 2009

    No mention of the sterilisation aspect? Cooking kills germs. This alone would be a sufficient reason to evolve a taste for cooked foods – especially for meat.

  23. #23 elsa
    June 23, 2009

    Thanks for the thorough review!
    Two comments:

    1. Just yesterday, this item went up on science daily http://tinyurl.com/msacec. Humans have a higher cancer rate than chimpanzees. The featured research tries to link that to humans having bigger brains, which may rely on decreased capacity for programmed cell death and hence decreased cancer-fighting ability. I can imagine lots of reasons humans might have more cancer than chimps, but, based on your post, it occurs to me that eating cooked meat with its carcinogenic byproducts might also be one of them?

    2. Did you know that Wrangham is going to be on The World Science Podcast this Friday (the 26th), and that he will be in the online forum to discuss and answer questions throughout the following week? http://theworld.org/science (Disclosure: Yes, I’m involved in producing the podcast!)

  24. #24 Sandgroper
    June 23, 2009

    toto – yes, but so do curing, smoking and drying. But cooking is faster. Trade-off – cooked meat lasts less time before it spoils, the other methods much take longer than cooking but preserve the meat for a much longer time.

    All of them are an advance on raw meat, except in relation to carcinogens which don’t influence reproduction.

  25. #25 The Mind Relaxer
    June 24, 2009

    Wow, that’s a long but very informative post. Let’s start cooking now,cause I really prefer cooked food and not the other one around. Very interesting.

  26. #26 MaxDWolf
    June 24, 2009

    Aside from animals fearing it (and I’m not certain this fear is as ubiquitous and overpowering as it’s made out to be), the other defensive value of fire is in the light it gives off. I understand one of our major predators in the early years were the big cats (still to be feared in places). Their night vision is much better than our own. Having a campfire would be one of the ways (among many) to even the odds a little at night.

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