The Role Starch in Human Evolution Part 1
Cultivating starch: rethinking the origins
Just how important was starch to human evolution? This question demands an answer because it bears directly on what humans eat today, on what we perceive the role of starch to be in the modern diet and how we view starch in relation to the epidemic of obesity and type II diabetes. It's also important because so many people buy the proposition that starch is somehow unnatural to humans or that starch was the downfall of human health and that we should eat more like our Paleolithic ancestors who consumed a diet of only meat, supplemented by fruits, vegetables, nuts, and seeds. It's important because so many people buy the claim that our genes are old and therefore, we can't adapt to food of more recent origin, a claim more appropriate to intelligent design than to evolution, more pseudoscience than science.Â
Does your dog understand you, think like you? Maybe it's because he or she eats like you? In the January 2013 issue of the journal Nature an article titled "The Genomic Signature of Dog Domestication Reveals Adaptation to Starch Rich Diet" directly contradicts the notion that it takes millions of years to adapt to a new food source.  In this article, researchers identified 10 genes that have key roles in starch digestion and metabolism: "We identify candidate mutations in key genes that provide functional support for an increased starch digestion in dogs relative to wolves." There's long been a debate about how domestic dogs evolved from wolves. Here researchers speculate that wolves adapted to the foods humans left lying around, foods rich in starch. Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves, constituted a crucial step in the early domestication of dogs. If wolves, obvious carnivores, could rapidly adapt to starch, why is it so difficult for humans, obvious omnivores?
Humans began cultivating grains, beans, roots, and tubers (the foods naturally rich in starch) about 11,000 years ago, abandoning this critical source of energy only where or when severe climate made cultivation impossible. Starchy foods now feed most of the world and provide the majority of the calories and protein. And if we began cultivating starches 11,000 years ago, it's a good bet that they were important to us long before that time. Our ancestors didn't suddenly one day quit hunting and gathering to begin cultivating crops about which they were clueless. Knowledge of their value must have gone back a very long time, but exactly how long depends upon what we mean by starch, a definition that carries with it no small degree of complexity.
What is starch?
Simply put, starches are chains of sugar (glucose) molecules that act as the primary energy store for the plant. This energy is stored in seeds (like grains and beans), roots, and tubers. Presently, starch is the most dominant human fuel on the planet. Grains and beans, roots and tubers are the foods of civilization. They are the staples of every ethnic cuisine. Can anyone imagine the Asian cuisine without rice and noodles, Italian cooking without pasta, Middle Eastern dishes without couscous or garbanzo beans, Irish cooking without potatoes or oatmeal, Mexican food without rice and Pinto beans? Before the advent of fast food, even the American cuisine was a melting pot that included staples like boiled potatoes, great northern beans, and cream of wheat. Need I go on? So, when did this dependence on starch begin?
When did we begin to use starch?
According to Harvard primatologist Richard Wrangham, roots and tubers, a.k.a. underground storage organs, were important sources of food for humans as early as 1.8 million years ago. That's about the time Wrangham believes human ancestors (there were many who lived currently) began to control fire. Cooking made many foods more palatable, easier to chew, and easier to digest, allowing greater access to calories. While it's easy to understand the effect of cooking on food, not all anthropologists agree with Wrangham's timing of the control of fire, putting it closer to 400,000 years ago, though still a discovery of Homo erectus. Whatever the precise timing, starches wouldn't have been important foods until we learned to control fire because we can't digest raw starch efficiently.
As discussed elsewhere on this website, starch must be gelatinized (heated in water so that starch granules swell and burst) in order for starch-digesting enzymes to access the starch chains. This could have been accomplished long before the ability to boil water, a relatively recent development. Roots and tubers can be thrown into an open fire and cooked because they carry their own water. However, after gelatinization (which occurs as the water inherent in roots and tubers boils), the high temperatures and dry conditions of the fire drives off most of the water, shattering the starch chains (a process called dextrinization) converting the starch effectively to sugar. Still these foods would have been an important source of calories that helped our ancestors to avoid protein toxicity, something hunter-gatherers struggle with on a daily basis because protein cannot be the primary source of fuel for humans to the nitrogen byproducts generated when converting protein into fuel. Thus the claim that starch wasn't important until we began cultivating food is pure nonsense based on the assumption that our ancestors never bothered to dig roots out of the ground when they were hungry.
When did starch act like starch?
Because throwing roots and tubers into an open fire dextrinizes the starch, the next question is: when did starch act like starch? In other words, when could we get the full benefit of starch, the full potential for glycogen storage? That would await an innovation equal in importance to any in our history; the ability to boil water. I proposed this hypothesis in 2001, and it is even more valid today. Boiling technology gave our ancestors access to the starch in grains and beans as sources of fuel and made roots and tubers much more efficient at promoting glycogen storage in muscles and brain. Boiled starch, functionally different sugar and dextrinized starch, could do for our ancestors what it does for us today: it greatly increased the ability to store glycogen in muscles and the brain. The best explanation for this is that boiled starch makes these cells more responsive to insulin, better at pulling glucose out of the blood. This would have a profound effect on our ancestors both mentally and physically.
Athletes intuitively understand the benefit of boiled starch in providing muscles with glycogen, though why boiled starch is so effective is never fully explained because we have always failed to recognize the distinction between boiled and baked starches, and still do. More to the point here is that glycogen has a powerful effect on the brain. It's not news that glucose is the primary fuel for the brain, with ketones acting as a partial substitute only during emergencies when carbohydrates are not available. What is news, however, is the role glycogen plays in the acquisition of long-term memory. A 2011 article published in the journal Cell titled Astrocyte-Neuron Lactate Transport is Required for Long-Term Memory Formation shows that glycogen in brain cells called astrocytes is necessary for the consolidation of short-term, transient memory into long-term memory.  The effect of glycogen cannot be imitated by glucose, regardless of quantity. Though this study was done in rats, it demonstrates an important principle. Glycogen, which consists of chains of glucose molecules like starch, provides both energy and information about what to do with that energy. For humans, boiled starch carries the information needed to store glucose as glycogen more efficiently than could be done in its absence. Access to the information carried by the starch molecule occurred as a direct result of the technology to boil water, an event that we know occurred at least 40-50,000 years ago, because that's when the telltale evidence of uniquely shattered stones, indication of stone boiling could be found.  This puts boiling technology concomitant with the rapid advance in the mental capacity of Homo sapiens. Often referred to as the Great Leap Forward or the Mind's Big Bang, this creative threshold our ancestors crossed ushered in all the advances we now associate with modern thinking. This is the best explanation for the transition from the Middle to the Upper Paleolithic Period made only by Homo sapiens. No other explanation can account for the time, for the rapid spread of mental ability throughout a population.
The Unheralded Role of Starch
Homo sapiens, our species, were anatomically modern some 200,000 years ago, but did not leave behind any indication that they were behaviorally modern, modern the sense of how we think and approach problems, or how we interact with each other until roughly about 40 or 50,000 years ago. We defined this time as the upper Paleolithic period. What's mysterious is that it happened with no change in anatomy. Our brain didn't get bigger, or anatomically more complex. Our brain apparently didn't physically change at all, but somehow we became a lot more mentally capable. So what happened?
Anthropologists have struggled for decades to account for this rapid mental advance, made only by Homo sapiens, by resorting to explanations that are highly improbable and unnecessarily complex. For example, they suggest that one or more brain mutations caused fundamental changes in either the language center of the brain or the areas that control executive functions. Mutations provide the necessary variation of traits to be selected from in response to environmental change, but they have no power in and of themselves to drive adaptation, especially of an entire population in a relatively short period of time. An innovation that affects the source of available food, however, has exactly that power, and there is plenty of precedent for this in human evolution, notably the development of stone tools and the control of fire, each of which expanded the food choices of our ancestors. The ability to boil water is just such an innovation.
Any mutation in brain function had to be secondary to a change in environment. That's how evolution works. It requires selective pressure. What we have completely ignored in this particular case is the selective pressure that we ourselves provided and have always provided innovation. Innovation provides selective pressure by changing the available food in the environment. It's happened before with profound results. In fact, the journey of human evolution is defined by innovation, by the ability of our ancestors to respond to and shape their environment. There were three seminal events in human evolution that allowed us to survive by expanding our selection of foods. The first of these was the development of stone tools which marked our entrance into the Paleolithic period. The second great innovation was the control of fire, which had the same dramatic affect. The story of fire and its effect on human evolution is told by Harvard primatologist Richard Wrangham in his book Catching Fire: How Cooking Made Us Human. The problem with Wrangham's thesis, however, is that it stops short of considering the effect of cooking at a critical time in our mental advance. It ignores the most important fundamental in carbohydrate nutrition when it comes to humans, that there are four macronutrients, not three. Therefore, Wrangham's argument can only account for access to calories, which requires only that our ancestors could control fire, not that they could boil water.
Boiled starch is a completely unique food, one that heretofore never existed, one that carries with it the information necessary to drive glycogen storage in an unprecedented fashion. In light of the Suzuki article, it is reasonable to suggest that the ability to boil water provided Homo sapiens the potential to go from local transient memory to consolidation into long-term memory, a trait that could quickly spread throughout an entire population as simply as the spread of a new technology, as easily as new cooking technique. This is the simplest and most practical explanation for the enigmatic transformation that characterizes only our species. As much as we like genetics as the answer, it takes time for genetic changes to happen, a lot of time, unless of course, they were in response to selective pressure. The ability to boil water provided that selective pressure.
The proposition that starch is unnatural to humans, that starch is the downfall of humanity couldn't possibly be more erroneous. In fact, absolutely the opposite is true. Homo sapiens are defined by starch. The movement into the upper Paleolithic period indicated by remnants of sophisticated stone tool technology, cave paintings, body decorations, musical instruments, and sophisticated tools and other materials is the result of starch. How we managed to overlook what seems so obvious is the subject of part 2.
1.Axelsson, Erik, et al. Nature 495, 360-364 (21 March 2013). 2.Suzuki, A., Stern, S.A., Bozdagi, O., Huntley, G.W., Walker, R.H., Magistretti, P.J., and Berini, C.M. (2011). Cell 144 810-823. 3.Bricker, H.M. (1995) Abri Pataud.