Chapter 5: Brain Foods

Having Your Cake and Efficiently Digesting It Too.

In Chapter Five, Wrangham discusses how our genus Homo experienced an evolutionary trade off, giving up big guts in order to grow big brains. Diverting more of our Basal Metabolic Rate (BMR) toward fueling our calorie-hungry brains, we had to compromise by shrinking the size of calorie-consuming stomach. Brains and stomachs, along with hearts, kidneys and livers, are the most expensive organs in the human body in terms of consumption of metabolic energy (Wrangham).  Aiello and Wheeler (1995), summarize this nicely in the following chart, which was reprinted (Billings, 1999):

Furthermore, the same source states:

“Since gut size is associated with dietary quality (DQ), and the gut must shrink to support encephalization, this suggests that a high-quality diet is required for encephalization. That is, a higher-quality diet (more easily digested, and liberating more energy/nutrients per unit of digestive energy expended) allows a smaller gut, which frees energy for encephalization.”

But was shrinking the size of the gastrointestinal track the only adaption that could have facilitated encephalization? I wanted to conduct a bit more research into morphological or behavioral options that could have allowed us to grow bigger brains, and to evaluate their validity.

Option 1. The Other Big Spenders

As previously mentioned, the heart, kidneys and liver also consume a large proportion of our energy. However shrinking any of these organs could have much greater consequences. The brain depends on glucose processed by the liver, so it has to be of a large enough size to function properly. This is especially important considering the brain has no glucose stores of its own and depends on that which flow through the blood stream (Aiello and Wheeler, 1995). The brain, if it was to increase in volume, would need even more glucose, so it is best not to shrink the liver. Aiello and Wheeler (1995) also state that shrinking the heart may compromise circulation which brings a constant flow of oxygen and nutrients to the brain, another unviable option. Finally, the kidneys have high metabolic rates as well, but compromising their function of removing waste products from the blood stream and processing urine would be especially dangerous in the habitats where water is limited, which is likely the case with Africa hominids (Aiello and Wheeler, 1995).

Option 2. Cheaper Cuts

Perhaps a reduction in skeletal muscle could balance out the energy budget? Not quite, because muscle tissue has a much lower BMR, so to offset the brain’s high BMR, much more muscle tissue would have to be eliminated, at least 70% (Aiello and Wheeler, 1995).  

Option 3: Have Your Cake and Eat it Too

Consume more calories, keep both. Sounds perfect, right? Aiello and Wells (2002) states increased BMR imply that an organism must either increase the quality or quantity of food. Increasing the quantity is unlikely, states the same source, because Homo ergaster needed adequate time for traveling, socializing and resting, not just for feeding. The same source purposes a drastic increase in diet quality, adding more soft bulbs and tubers and increasing meat consumption. And not surprisingly, the increased nutritional content of cooked food would help too—this leads back to support Wrangham’s original hypothesis. Therefore, it appears after a brief comparison that the shrinking of the GI track may be the most energy efficient way to balance out encephalization. 


Also: Wrangham brings up the curious case of the walking science experiment Mr. St. Martin, whose open-air stomach led to the discovery of the digestive process. Learn more at: radiolab.org

Resources:

Aiello L, and Wheeler P. 1995. “The Expensive-Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution.” Current Anthropology. 36:199-221

Aiello L, and J.C.K. Wells. 2002. “Energetics and the Evolution of the Genus Homo.”  Annual Review of Anthropology. 31:323-338.

Billings T. 1999. “Comparative Anatomy and Physiology Brought Up to Date: The Relationship of Dietary Quality and Gut Efficiency to Brain Size.” Available at www.beyondveg.com

Wrangham, R. 2009. Catching fire: how cooking made us human. New York: Basics Books.

Chapter 4: When Cooking Began

First Ingredient, Solid Case Studies

                Wrangham begins this chapter by acknowledging the great discrepancy over the approximate date for the beginning of cooking in human evolution. The fact seems so obvious I’d like to gloss over this a bit a fast forward to the part of the chapter that interested me the most. Wrangham states that by searching the fossil record for morphological changes (many of which are chronicled and explained in previous blogs) we can put our finger on when cooking began by the adaptions it caused. He uses the parallel argument that because many animals respond to dietary changes with inheritable adaptions, humans could have to. I would agree with this, except I think he uses a poor example:

“Studies of Galapagos finches by Peter and Rosemary Grant showed that during a year when finches experienced an intense food shortage caused by an extended drought, the birds that were best able to eat large and hard seeds—those birds with the largest beaks— survived best. The selection pressure against small-beaked birds was so intense that only 15 percent of birds survived and the species as a whole developed measurably larger beaks within a year. Correlations in break size between parents and offspring showed that the changes were inherited (Wrangham, 2009).

Now, I don’t think this is a proper example—it appears a bit too “apples to oranges.” Here’s why: in the case for cooking causes evolutionary adaptions Wrangham agrees that the nutritional benefits of food changes the bodies of hominids in an inheritable way. Here it is not the nutritional value (or a food processing method that increased the nutritional value) of food that is being evaluated, but the scarcity of the resource. This would make sense as an analogy to the theory that Robust Australopithecines (with extremely strong chewing apparatuses) may have gone extinct because they were too specialized and could not adapt when food availability favored a more gracile set of chompers. To present a strong argument for his point, I think Wrangham needs to find an example that says perhaps “birds eating nuts with impressive protein levels showed increased wingspan and muscle development.” Now that is made up, but I set out to find some examples of studies that I believed better support what Wrangham was trying to prove through this analogy.

To be honest, the related research I could find was limited. I read a case study detailing how mice exposed to a high-fat diet experience heritable changes in their gut microbial and metabolic phenotypes, but not a study that spoke of the link between diet changes and drastic phenotypic change in other animals (Serino M, et al., 2011). I feel like this argument is crucial to Wrangham’s book, and he could have spent more time on his supportive examples here.

References:

Serino M et al. 2011. Metabolic adaption to a high-fat diet is associated with a change in the gut micribiota.  Available online at http://gut.bmj.com/content/early/2011/11/22/gutjnl-2011-301012.full.pdf.

Wrangham R. 2009. Catching fire: how cooking made us human. New York: Basics Books.

Chapter 3: The Energy Theory of Cooking

Chapter 3: The Energy Theory of Cooking

Enter Junk Food

            In this chapter, Wrangham presents arguments based on nutritional science how cooking facilitates food digestion (I think he may be getting redundant at this point….). In summary, he states that although cooking may have adverse effects on the nutritional content of food (energy losses through drippings, the production of inedible compounds and a reduction in vitamins) it does make what nutrients remain easier to digest by breaking down the cell walls or plant matter and tenderizing meats (Wrangham, 2009). He asserts, at the end of the chapter, that because female members of the genius Homo cooked and could therefore get more nutrients, they had healthier babies, higher reproductive success and passed on more genes than ancient raw-foodists.

            The importance of consuming high-nutrition foods during pregnancy is clear. But in this day and age it may be taken too far.  New research done by the Royal Veterinary College of London suggests that food preferences can be passed down from mother to unborn child, especially those for high calorie, high sugar and high cholesterol foods. Their research found that rats that ate diets high in fat, salt and sugar while pregnant produced offspring who were more likely to prefer the same diet as opposed to regular feed (Boyal et al., 2008). Another study from the Journal of Physiology indicated that these young rats bodies’ retained negative effects to their metabolism long past their junk food filled-adolescence (Science Daily, 2008).

            Are there similarities between pregnant women and pregnant rats? Research shows that the heavier a woman became during pregnancy the more likely she was to have an obese child (Oken et al., 2008).  The same study shows the female children shows signs of high levels of leptin –the hormone that induces appetite, making them more susceptible to over eating.  Therefore, nutritionist Dr. Stephanie Bayol states: “We always say 'you are what you eat'. In fact, it may also be true that 'you are what your mother ate.' This does not mean that obesity and poor health is inevitable and it is important that we take care of ourselves and live a healthy lifestyle. But it does mean that mothers must eat responsibly whilst pregnant" (Science Daily, 2008).

            Wrangham states that passing nutrition and a preference for cooked food from mother to child with crucial in the success of our early ancestors (Wrangham, 2009). I find it interesting that now the same trend, plus Twinkies, little Debbies’ and Frittos, may again affect our evolutionary success. As obesity and related diseases occur with increasing frequency within the industrialized world, it will interesting to see if society’s attention switches from a fixation on slim-cut jeans, to addressing the genes themselves.

References:

Bayol S, Simbi B, Bertrand, and Stickland N. 2008. Offspring from mothers fed a "junk food" diet in pregnancy and lactation exhibit exacerbated adiposity which is more pronounced in females. The Journal of Physiology. 586:3219-3230.

Oken E, Taveras E, Kleinman, K, Rich-Edwards, J and Gillam M. 2008. Gestational weight gain and child adiposity at age 3 years.  American Journal of Obstetrics and Gynecology. 196:322.

Wrangham, R. 2009. Catching fire: how cooking made us human. New York: Basics Books.

--- 2008. Poor Diet During Pregnancy May Have Long Term Impact On Child's Health, Study Suggests. Science Daily. Available online at: http://www.sciencedaily.com/releases/2008/06/080630200951.htm

Chapter 2: The Cook's Body

The Trade Off: Little Jaws, Big Brains?

In Chapter Two: The Cook’s Body, Wrangham discusses the morphological differences between human and ape digestive systems. As predicted, he contributes most of these to cooked food. However, other factors should be considered, such as random gene mutations. I want to summarize these changes quickly before exploring the article I want to bring up. In brief some of the changes mentioned are:

1.       MINISCULE MOUTHS and LIPS:

Humans, as compared to other primates, have relatively small mouth compared to body size; our mouths fit the same amount of food as that of a chimpanzee, although humans weigh on average twice as much as chimps do. (Wrangham, 2009).  Chimpanzees also have much stronger lips, used to compress food against their teeth. Human lips are small, and together with the mouth can only accommodate a relatively small amount of food at a time (Wrangham, 2009)

2.       WEAKER JAWS and TINY TEETH

Human masticatory muscles (the temporalis and the masseter) reach only to about the tops of our ears, where as many apes have larger sagittal crests than anchor chewing muscles from their strong, robust jaws to the tops of their craniums. You would have to trace back along our evolutionary timeline to the robust Australopiths to find such masticatory equipment.  We also have smaller, weaker muscle fibers in our jaws (Wrangham, 2009). This is important, and we’ll return to this in the journal article. Also, after millions of years of soft food items, Wrangham, (2009) believes our early Homo chefs developed more diminutive teeth, because cooked food requires less grinding and shredding.

3.       SMALLISH STOMACHS

The surface area of the human is only 1/3 the expected size for a primate of our body weight- that’s smaller than 97% of other primates (Wrangham, 2009). According to the same author this may be because, eating foods of low quality, gorillas and other apes have to ingest much more food to break even on their caloric intake.

4.       ITTY-BITTY INTESTINES

Finally, while the human small intestine is only a little smaller than the predicted size for a primate of our body weight, our large intestine is 60% less than the expected mass for that organ (Wrangham, 2009). According to Wrangham (2009), this is likely because the colon is where tough fibrous plants ferment in other primates, and through cooking we have largely decreased the amount of difficult-to-digest roughage we consume.

                Returning to the diminutive jaw muscles. Could our little jaws be due only to changes in diet? Could our loss of sagittal crests and large masticatory muscles have played a role in the development of our bigger brains? Stedman et al. (2004) conducted research linking the myosin heavy chain (MYH) Wrangham mentions with the evolutionary trend of encephalization.  This is attributed to a frameshift mutation and loss of the protein that produced larger, powerful masticatory muscles.  Stedman et al. (2004) believes this mutation occurred at approximately 2.4 million years ago, and that without the constraints of sagittal cresting and larger chewing muscles, are craniums could expand to house larger brains. But the advent of cooking, according to Wrangham, occurred ~1.9-1.8 million years ago. Therefore, I think Wrangham could consider other factors in our morphological changes besides those instigated by softer, more nutritious diets. Cooking may have led to morphological change, but considering the research done by Stedman et al. (2004), cooking may have just further spurred on changes long in the making, and independent of our dietary preferences.

References:

Steman H, Kozyak B, Neilson A, Thesler D, Si L, Low D, Bridges C, Sheager J, Minugh-Purvis, N and Mitchell M. 
  2004. Myosin gene mutation correlates with anatomical changes in the human lineage. Nature.   426: 415-419.

Wrangham, R. 2009. Catching fire: how cooking made us human. New York: Basics Books.

Chapter 1: The Quest for Raw Foodists

Half Baked: The Raw Foodism Movement

In Chapter One: the Quest for Raw-Foodist, Wrangham explores the Giessen Raw Foods Diet. He investigates the reasons for and implications of abstaining from cooked food. Participants in raw-food diets report “a sense of well-being, better physical functioning, less bodily pain, more vitality…improved emotional and social performance…reductions in rheumatoid arthritis and fibromyalgia symptoms, less dental erosion, and improved antioxidant intake” (Wrangham, 2009). However, the qualitative results may be more along the lines of vitamins deficiencies (especially of B12), decreased levels on HDL (the good cholesterol) and low amounts of homocysteine (lack of which may lead to heart disease) (Wrangham, 2009). Raw food diets (in nature as well as in the “1st world”) are especially tough on women, and lead to severe weight loss, amenorrhea, loss of menstrual cycle and decreased fertility (Wrangham, 2009).

A former vegetarian myself (who returned to meat after chronic anemia) I decided to investigate deeper into the nutritional validity of raw foods. “Raw-foodists, it is clear, do not fare well,” asserts Wrangham (2009) at the conclusion of the chapter. This implies cooking is superior (if it was so bad for us, wouldn’t we have stopped several hundreds of thousands of years ago?). But, let’s explore the nutritional science a bit more thoroughly.

According to Food Writer Scott Kustes, the central claim of the Raw Foods Movement is that “that cooking denatures or destroys essential enzymes in the food, that all food has a kind of 'life force' that is killed off by cooking.” (Kustes, 2012). Raw foodists claim that these “natural enzymes” are essential for proper digestion (Better Nutrition, 2004). They also believe cooked food is the cause of many of the chronic diseases and obesity that effect industrialized nations (Biali, 2006). Therefore, digesting raw food is better for you (more natural, more energy efficient etc.) than cooked food, considering our evolutionary ancestors and great ape cousins ate or eat mostly raw plant matter.

However, cooking has obvious nutritional benefits, are here are the most well-known. Cooking tough fibrous foods makes them 2-12 times more digestible as compared to their raw forms, especially for foods of high nutritional values like legumes, grains and seeds (Kustes, 2012). Some vegetables actually release more nutrients when heated and consumed (such as garlic and diallyl, which lowers blood pressure). Also, according to Kustes (2012) cooking helps break down some anti-nutrients (the plant’s evolved chemical defenses). Kustes (2012) gives the example of soy, whose trypsin inhibitors and lectins (cytotoxins) are neutralized by heating.

As Wrangham states, the negative effects of a raw the diet may very well surpass the aforementioned “benefits.” Weight loss may be the most obvious consequence. According to a study done by Koebnick et al. (1999), in long term raw food diets (3.7 years), men loose approximately 9.9kg and women loose about 12 kg. For 30% of the women in the same study, this caused partial to complete amenorrhea. The study concluded that because “the consumption of a raw food diet is associated with a high loss of body weight. Since many raw food dieters exhibited underweight and amenorrhea, a very strict raw food diet cannot be recommended on a long term basis” (Koebnick et al, 1999). Besides malnourishment and amenorrhea, the deficiencies in raw food diets can cause loss of bone mineral density and rotten teeth (Biali, 2006). Ironically, because raw foodists often ingest a high proportion of citrus fruits, they have significantly MORE dental erosion (Ganss C. et al., 1999). Looks like even a purposed benefit of the raw food diet is a detriment.

Against the basic benefits of cooking food, and the numerous deficiencies and negative effects of  consuming only raw foods, straight nutritional science has me erring on the side of “well-done.”

References:
Anonymous. 2004. Are raw foods a raw deal? Better nutrition. 66:19.
Biali, S. 2006. The raw foods diet: a raw deal? Med Post. 42: 25.
Ganss, C, Schlechtriemen M, Klimek J. (1999). Dental erosions in subjects living on a raw foot diet. Caries Research. 33: 74-80.
Koebnick C, Strassner C, Hoffmann I, and Leitzmann C. (1999). Consequences of a long-term raw food diet on body weight and menstruation: results of a questionnaire survey. Ann Nutr Metab. 43: 69-79.
Wrangham, R. 2009. Catching fire: how cooking made us human. New York: Basics Books.
Kustes S. 2012. Are Raw Vegetables Healthier Than Cooked Vegetables?. In Real Food University. Retrieved March 7, 2012, from http://www.realfooduniversity.com/

Introduction

A Taste of What Made Us Human.

We all know cooking food has immense historical, cultural and social significance.  There are a myriad of publications and pop media (from “The Joy of Cooking” to “Iron Chef” on the Food Network) about it, professions developed around it, and passions exploring and exploiting it. Much of our universal culture hinges on our preparation and consumption of edible substances. Yet this simple act is often over-looked in our daily lives, and perhaps even more so, in our evolutionary history.

In his book “Catching Fire: How Cooking Made us Human,” Richard Wrangham, a renowned primatologist and anthropology professor at Harvard University, explores how cooking doesn’t just enrich the human experience, but possibly created it. “Cooking increased the value of our food. It changed our bodies, our brains, our use of time and our social lives,” (Wrangham, 2009). In the introduction to his book, Wrangham looks for the dietary stimuli to major morphological changes in our evolutionary time line. Specifically, Wrangham and many of his contemporaries are interested in the evolutionary transition that took place between 1.9 and 1.8 million years ago, when Homo habilis gave way to Homo erectus.  If the transition to a more carnivorous diet may have facilitated the rise of the genus Homo from our Australopithecine ancestors, Wrangham hypothesizes, then there must be a second, different impetus that made Homo erectus so successful. Could it have been the advent of cooking?

There are many arguments (Wrangham’s included) that seek to link the increased nutritional value of cooked found with evolutionary encephalization. Cooking meat makes proteins easier to absorb, and increases the amount of energy actually digested and processed by the consumer (Leung, 2011). Likewise, tough fibrous vegetables are broken down; cooking softens the plant cell walls, and once this roughage is chewed it is much easier to digest (Brahic, 2010). In comparison with other primates like chimpanzees, humans consume a relatively low amount of indigestible fibers (30% compared to 10% respectively), according to Wrangham in an interview with Townsend (2006). The extra caloric uptake from more easily digestible food maybe have allowed early humans to travel further, grow taller, and develop a larger proportion of energy-expensive organs (like big brains), states Wrangham in the same interview. Also, at the end of their linage, the robust Australopithecines had massive masticatory muscles, large anterior teeth and jaws capable of high-bite forces (Strait, 2010). Early members of the genus Homo on the other hand developed smaller teeth, more delicate jaws and flatter faces (Townsend, 2006). In his book, Wrangham explores the role of cooking in the morphological, social, and cultural developments that occurred between the Australopithecines and modern Homo sapiens. In this blog, I will be exploring and further expanding upon each topic he brings up, chapter by chapter. So grab a torch, catch the fire, and come along.

References:

Brahic, C. 2010. Chew on this: thank cooking for your big brain. The New Scientist 207: 1-12

Leung, W. 2011. How cooking may have affected human evolution. The Globe and Mail. 

Strait, D. 2010. The Evolutionary History of the Australopiths. Evo Edu Outreach. 3:341-352.

Townsend, E. 2006. The cooking ape: an interview with Richard Wrangham. Gastonomica. 5: 29-37.

Wrangham, R. 2009. Catching fire: how cooking made us human. New York: Basics Books.