Catching Fire: How Cooking Made Us Human - Critical Analysis
After reading a comment in a Facebook group the other day and posting my own comment (with citations) supporting my understanding that human brain growth preceded our use of fire. I was urged by a couple of members to read the book Catching Fire: How Cooking Made Us Human by Richard Wrangham, which supposedly supported their understanding that it was use of fire to cook food that created the larger brains in humans.
After purchasing the book (because I didn't want to be considered 'close-minded'), and following the author through a tortuous path of tortured logic, I'm beginning to wish I'd simply shut up and refrained from making the comment in the first place, allowing the respective members embroiled in the debate to continue as they liked. However, I'd made the plunge so now I'm following up with my opinion of the book.
Introduction The Cooking Hypothesis
The introduction of the book starts reasonably enough with the description of our ancestors creating and using stone tools for cutting meat some 2.6 million years ago. The transition at that time from the more ape-like Australopithecines to the Habilines is explained easily enough by meat becoming part of the diet. Wrangham has difficulty with the next transition 1.8 million years ago from Habiline to Homo Erectus, which he ultimately puts down to the use of cooking. He has difficulty rationalizing the smaller jaws with the ability to eat raw food:
"a key problem concerning the anatomy of Homo erectus, which had small jaws and small teeth that were poorly adapted for eating the tough raw meat of game animals. These weaker mouths cannot be explained by Homo erectus's becoming better at hunting. Something else must be going on."
At no point does he consider climate change, a period of cooling (as happens on a cyclic basis every 100,000 years or so), as being a possible driver that caused our early ancestors to be reliant on meat in the diet as opposed to plants. That possibility of having even greater amounts of meat in the diet causing our brains to become larger yet again.
He finishes the introduction with the idea that it is 'cooking' that makes us human and supports it with the curious assertion that:
"cooking increases the amounts of energy that our bodies obtain from food"
I say 'curious' because, in the last 15,000 years of civilization it seems that increasing the energy we obtain from food has mainly been associated with a decrease in the size of our brains as we've become better at breeding plant species and processing them and making them again a main staple of our diet. Furthermore, our civilization, now divorced from the 'hands on' involvement in capturing, killing and butchering animals for food, has given rise to a new breed of human, the vegetarian/vegan. A study by Oxford University showed:
"Using tests and brain scans on community-dwelling volunteers aged 61 to 87 years without cognitive impairment at enrolment, they measured the size of the participants' brains. When the volunteers were retested five years later the scientists found those with the lowest levels of vitamin B12 intake were the most likely to have brain shrinkage. Not surprisingly, vegans who eschew all foods of animal origin, suffered the most brain shrinkage. This confirms earlier research showing a link between brain atrophy and low levels of B12.
Vegans are the most likely to be deficient because the best sources of the vitamin are meat, particularly liver, milk and fish.
There were two other worrying aspects to this trial. The first was at the start of the trial, the biggest brain in a vegan, at 1455 ml, was already smaller than smallest brain of someone on a ‘normal diet’, at 1456 ml."
All said and done, if you are going to define humans as 'cooks' and the reason we became humans as 'cooking', then there is really nothing to be argued. I probably shouldn't have gotten involved in the debate.
Chapter 1 Quest for Raw Foodists
In the first chapter we are asked to consider the Evo diet. The Evo diet appears to be a raw plant food diet - later supplemented with cooked fish.
We take nine seriously unhealthy people and put them on an experimental raw vegetarian diet for about 2 weeks (12 days I worked out). They eat up to 5 kg per day until they are full of fibre and this works out to be around 2000 kcal per day. Their cholesterol levels and blood pressures drop and so does their weight. This is what Natasha Campbell McBride has called a fast. This has proven that the human body is not good at obtaining nutrients from raw plants, but that a lack of nutrients for a period of time can be a healthy intervention for a group of people who have become sick from eating a standard western diet for a few decades.
Next, the chapter suggests a cooked vegetarian diet is the same energy value as a cooked meat rich diet. Shows data that indicate a raw vegetable diet contributes to poor weight gain.
"The amount of meat in the Giessen Raw Food diets was not recorded but many raw-foodists eat rather little meat. Could a low meat intake have contributed to their poor energy supply? It is possible. However, among people who eat cooked diets, there is no difference in body weight between vegetarians and meat eaters: when our food is cooked we get as many calories from a vegetarian diet as from a typical American meat-rich diet. It is only when eating raw that we suffer poor weight gain."
Not only poor energy supply but what about adequacy of nutrients? Is he really suggesting that calories is the important feature here? He is using data from people eating basically raw vegetarian diets and saying that these will be equivalent to raw meat diets in terms of nutritional inadequacy?
Next, to illustrate energy insufficiency, Wrangham mentions absence of menses on a raw food diet.
"Healthy women on cooked diets rarely fail to menstruate, whether or not they are vegetarian. But ovarian function predictably declines in women suffering from extreme energy depletion, such as marathoners or anorexics."
Another illustration of how a raw plant diet is not good for the survival of the species.
Indeed much of the chapter is discussing the problems of obtaining nutrition from raw plants - something I can agree on. There is not much study of what happens on a raw animal-based diet but he does discuss one case where a family were stranded in a lifeboat after their boat sank. This family spent 38 days in a boat and had to eat what they could catch for the last 31 days (when they no longer had access to sugar - cookies and candy). They emerged healthier than when they started. However they missed the cooked foods they had traditionally eaten.
From this he concludes:
"The lack of any evidence for longer-term survival on raw wild food suggests that even in extremis, people need their food cooked." [Bold emphasis my own]
Chapter 2 The Cook's Body
In chapter 2, Wrangham continues to assert that cooking achieves energy advantages and illustrates it by trying to draw an inference that cooking pet food is what causes our cats and dogs to become fat.
"The spontaneous benefits of cooked food explain why domesticated pets easily become fat: their food is cooked, such as the commercially produced kibbles, pellets, and nuggets given to dogs and cats. Owners of obese pets who recognize this connection and see cooked food as a health threat sometimes choose to feed raw food to their beloved ones to help them lose weight. Biologically Appropriate Raw Food, or BARF, is a special diet advertised as being beneficial for dogs for the same reason that raw-foodists advocate raw diets for humans: it is natural."
No elucidation here as to the macro-nutrient constituents of the "commercially produced kibbles, pellets, and nuggets given to dogs and cats". Just that cooked commercial foods make pets fat and Biologically Appropriate Raw Food makes them healthy again.
The chapter goes on to describe changes to our anatomy including weaker jaw muscles.
"Our small, weak jaw muscles are not adapted for chewing tough raw food, but they work well for soft, cooked food."
And raw meat, I suspect. (At least my jaw muscles make short work of raw meat.)
The gut comes into the dialog as having been reduced in size - in his view because we cook food.
"Thanks to cooking, very high-fiber food of a type eaten by great apes is no longer a useful part of our diet. The suite of changes in the human digestive system makes sense."
While the author correctly attributes the reduced size of the large intestine in humans to the fact that we no longer have to digest large amounts of fibre that the great apes do, he neglects to mention that we developed a gall bladder so we could store bile produced by the liver that will help us digest and get energy from ingested fats.
Gorillas also get their energy from fats, but not exogenous fats like us. Their greater intestinal capacity allows for bacteria to digest fibre and convert it to fat for their energetic purposes. It is the ingestion of meat and preformed fats that has prompted this change in our "suite of changes in the human digestive system".
Chapter 3 The Energy Theory of Cooking
In this chapter, the author quotes "authoritative science" as saying that there is no effect of cooking on energy content of foods. Yet he finds this puzzling in light of his own grasp of the science of nutrition where he asserts:
"Obviously it conflicts with the abundant evidence that humans and animals get more energy from cooked foods."
He appears to be getting out of his depth here and delves into his own belief system in spite of what he reads from scientists and nutritionists. He is also perhaps, over-subscribed to the belief system of the 'calories in calories out' cadre - largely inhabited by old-school doctors, some 'big food' subsidized nutritionists, and 'bro-science' gym proprietors.
"Although different nutritionists say that cooking has no effect on the caloric content of food, or increases it, or decreases it, we can clear up this confusion. As indicated by the evidence from raw-foodists and the immediate benefits experienced by many animals eating cooked food, I believe the effects of cooking on energy gain are consistently positive." [Bold emphasis my own]
Unable to show any science for the increased digestibility of cooked meat over raw, he turns to a study done on the cooking of eggs increasing digestibility, This perhaps may be true for eggs, however we are really interested in meat from animals (particularly large ruminants) as that is what we think may have produced the massive changes in our increased brain size. After a little searching on the Internet I myself have managed to find this study:
Compared with Raw Bovine Meat, Boiling but Not Grilling, Barbecuing, or Roasting Decreases Protein Digestibility without Any Major Consequences for Intestinal Mucosa in Rats, although the Daily Ingestion of Bovine Meat Induces Histologic Modifications in the Colon.https://academic.oup.com/jn/article/146/8/1506/4584673
Shows that cooking meat will actually not make much difference to the Total Ileal Digestibility of proteins (unless boiled - in which case it reduces it).
"Conclusions: Boiling bovine meat at a high temperature (100°C) for a long time (3 h) moderately lowered protein digestibility compared with raw meat and other cooking processes, but did not affect cecal bacterial metabolites related to protein fermentation. The daily ingestion of raw or cooked bovine meat had no marked effect on intestinal tissues, despite some slight histologic modifications on distal colon."
Notwithstanding evidence to the contrary, Wrangham goes on to assert as fact that we (and other animals) get more energy out of cooked foods - regardless of what they are - animal or plant.
Where he is getting confused perhaps is the nutrient values. Cooked and processed plants certainly yield more digestible nutrients than the raw variety. However the nutrients they yield are typically sugars which simply become glucose and not much else. While this provides the body with energy, it leaves it lacking in some of the building blocks you might think would be necessary to grow a bigger brain, like amino and fatty acids. Cooking and fermenting plants will certainly render less harmful some of the toxins they contain, thereby incidentally making them more useful. Meat, on the other hand, requires no such processing to make it yield up the amino and fatty acids we need to repair our cells and create new ones. While it may require slightly longer to denature in the stomach (Wrangham insists that it only partially denatures), raw animal protein will nevertheless be fully dissolved by the time it gets to the ileum and is ready for full absorption by the digestive system.
Our bodies require a certain amount of energy to go about our daily business. If the food we eat doesn't have the required amount of energy we either eat more or do less business. While bigger brains require more energy in order to grow, it isn't the energy that causes them to grow, otherwise they would still be growing - because we are now feeding them more energy than ever!
Wrangham places a lot of emphasis on plants becoming more important to us once cooking allows them to become more digestible. I put it that, rather than this factor increasing our brain size, the fact we've moved away from a more meat rich to a plant rich diet in the last 30,000 years has been the reason our brains have decreased in size.
With such a small gut with which to absorb all the nutrients and energy our bodies need, a modern low-calorie, low-fat, fibre-rich, plant-based diet is woefully inadequate as an energy source for our energy-hungry system to function at peak efficiency. That lack has begun to show.
Since the advent of agriculture, there has been a worrying trend as our brains have actually decreased in size. A recently updated and rigorous analysis of changes in human brain size found that our ancestors' brain size reached its peak with the first anatomically modern humans of approximately 90,000 years ago. That then remained fairly constant for a further 60,000 years. Over the next 20,000 years there was a slight decline in brain size of about 3%. Since the advent of agriculture about 10,000 years ago, however, that decline has quickened significantly, so that now our brains are a further 8% smaller. That is a total of 11% smaller than at their peak size.
This suggests some kind of recent historical deficiency in some aspect of overall human nutrition. The most obvious and far-reaching dietary change during the last 10,000 years is, of course, the enormous drop in consumption of high-energy, fat-rich foods of animal origin which formed probably over 90% of the diet, to as little as 10% today, coupled with a large rise in less energy-dense grain consumption. This pattern still persists; it is even advocated today: it is the basis of our so-called 'healthy' diet."
Chapter 4 When Cooking Began
This chapter I have no argument with, it matters not, whether the consensus changes to go with Wrangham's theories of control of fire taking place several hundred thousand years earlier than current evidence suggests, just as long as the cooking was primarily meat with a few tubers thrown in.
Chapter 5 Brain Foods
Wasn't what I expected from the title - I thought it may have been about the particular nutrients that might be supposed to contribute to growing a brain. Instead it is more speculative navel-gazing about why we might have bigger brains and generally asserting that it must have been cooking that caused it. Already discussed in other chapters and repeated in this one. It does touch on the 'expensive tissue hypothesis' however, which is probably handled better in this blog of Dr. Michael Eades - Are We Meat Eaters or Vegetarians - Part II - if you want a better understanding. Also Eades properly attributed this understanding to Max Kleiber who originally formulated the law the work was based on.
Chapters 6, 7 and 8
Mainly relate to how cooking frees men and enslaves women in the patriarchal society and discusses other useful aspects of fire. I choose not to discuss these as they are not that crucial to the main point of the book and serve as filler to give the book some volume.
It is more logical to me that early ancestors started eating meat, possibly from scavenging, and this caused their brain to grow, probably because of a better, more suitable mix of nutrients than were available from plants - not more energy. The increased intelligence saw them using tools like sharp rocks to cut meat, and, eventually, fire to cook foods and keep warm and safe at night.
Use of tools to eat meat evident 2.6 million years ago. 2.3 million years indicates a species, 'habiline' which had a brain twice as big as a non-human ape. This shows that the encephalization process occurred prior to 2.3 million years ago and that tools were being used at that point, in the absence of fire and cooking. This MUST indicate that early ancestors were doing something else that was growing the brain - that something else was likely the ingestion of raw meat.
Wrangham's basic premise has been that our brains have grown bigger because of the extra energy imparted by food through cooking. Although he concedes it was the introduction of meat that started the process 2.4 million years ago, he thinks that the next big step was that we learned to control fire and used it for cooking foods and that was the way we released the extra energy from foods.
While he is able to show that cooking plants makes them more digestible, he fails to show where any 'extra' energy comes from. He is unable to produce any scientific evidence that cooking meat produces any extra energy but then shifts the goalposts to 'digestibility'. Again he cannot show any evidence for any significant ease in digestibility for cooked meat so shifts focus to eggs - which apparently there is some science to show that cooked will digest better than raw.
All his assertions about cooked yielding more energy than raw are illustrated by people eating mainly raw plants as opposed to cooked foods in general. He suggests that that vegetarians who cook their food are the same weight as omnivores who cook their food and therefore failure to thrive on a raw plant diet will suggest failure to thrive on a raw meat diet. It is a total failure of logic. His preoccupation with focussing on plants as is pretty much reflective of how our society in general regards them.
If it is energy density of foods that has been the driver of our increased brain size then how does he account for the fact our brains have been decreasing in size over the last 30,000 years - the time when we have been steadily increasing the energy we've been able to get out of plant foods by selective breeding and refining?
My alternative theory is that the move away from plants to a more NUTRIENT rich animal-based diet is what sparked our brain growth. Various glacials in the interim have made us even more reliant on the nutrient rich animal foods and prompted further spurts in brain growth.
Agriculture/civilisation has seen us move back to a greater reliance on plant foods and this has seen us decrease our brain size. Plants are proving to be nutrient poor compared to animals and we are now seeing the 'diseases of civilisation' - obesity, diabetes, cancer, heart disease, autoimmunity and dementia as we eat more and more energy-dense nutrient-poor foods, starving our body and brain of nutrients we've evolved on.