Reconstructions of human evolution tend towards simple, overly cluttered scenarios. Our ancestors, for example, stood on two legs to look over tall grass, or began to speak because they finally had something to say. Like much of our understanding of early hominid behavior, the presented diet of our ancestors has been oversimplified.
Take the trendy paleo diet, which is based on the way people lived in the Paleolithic or Stone Age from around 2.6 million to 10,000 years ago. It encourages practitioners to forego the fruits of modern culinary advances – such as dairy, farm products and processed foods – and to live a pseudo-hunter-gatherer lifestyle, much like Lon Chaney Jr. in the film One Million BC. Adherents recommend a very specific “Ur-Menu” that contains a certain proportion of energy from carbohydrates, proteins and fats and recommends a level of physical activity. These regulations are based primarily on observations of modern humans living at least partly as hunters and gatherers.
From a scientific point of view, however, such simple characterizations of our ancestors’ behavior are generally not correct. Recently, my fellow anthropologist C. Owen Lovejoy and I have delved deeply into this crucial question in human behavioral development: the origins of hominid nutrition. We have focused on the earliest phase of hominid evolution, approximately 6 to 1.6 million years ago, both before and after modified stone tools were first used. This time frame includes, in order of appearance, the hominids Ardipithecus And Australopithecusand the earliest members of our own genus, the comparatively intelligent homo. None of these humans were modern humans who appeared much later, but our distant ancestors.
We have examined the fossil, chemical and archaeological evidence, and also delved deeply into the foraging behavior of living animals. Why is that so important? Even observing animals in nature for an hour provides a clear answer: Almost everything an organism does every day is simply related to staying alive; This includes activities such as feeding, avoiding predators, and preparing to breed. This is the evolutionary way.
What did our ancestors actually eat? In some cases, researchers can use modern technology to study the question. Researchers study the chemical composition of fossil tooth enamel to find out the relative amounts of food hominids ate from woody plants (or the animals that ate them) compared to outdoor plants. Other scientists look in the old tartar for pieces of silica from plants whose type can be identified – for example, fruits of a certain plant family. Others examine the small battle marks left by stone tools on animal bones. For example, researchers have found that hominids ate the flesh and bone marrow of antelopes as early as 2.6 million years ago; Whether they were hunted or captured is hotly debated.
Such techniques are instructive, but ultimately only paint a blurry picture of nutrition. They provide good evidence that the underground storage organs of plants (such as tubers), sedges, fruits, vertebrates and vertebrates, leaves, and bark were part of the diet of at least some early hominids. However, they do not tell us anything about the relative importance of different foods. And since these foods are eaten, at least occasionally, by live monkeys, these techniques don’t explain what makes hominids different from other primates.
So how should we proceed? As my colleague Lovejoy says, to reconstruct hominid evolution, you have to use the rules that apply to beavers to create a human. In other words, you need to look at the “rules” of foraging. We’re not the first researchers to look into this. As early as 1953, anthropologists George Bartholomew and Joseph Birdsell attempted to characterize early hominid ecology by applying general biological principles.
Fortunately, ecologists have long been compiling these rules in a research area called optimal foraging theory (OFT). OFT uses simple mathematical models to predict how certain animals would forage under certain circumstances. For example, given a set of potential foods with estimated energy value, occurrence, and processing time (how long it takes to acquire and consume them), a classic OFT model calculates which resources should be eaten and which should be ignored. One prediction—a sort of “golden rule” of foraging—is that an animal should specialize in profitable foods (those high in energy and low in processing time) in abundance, but when they are scarce an animal should expand its diet.
Data from living organisms as diverse as insects and modern humans are generally consistent with such predictions. In the Nepalese Himalayas, for example, perched gray langurs avoid the leathery mature evergreen leaves and certain types of roots and bark for most of the year — all of which are low in calories and high in fiber and plenty of processing time. But in the harsh winter, when better food is scarce or unavailable, they gorge on it.
In another, more controlled study, when varying amounts of tonsils were buried in or out of the shell, chimpanzees were able to later recover larger amounts (more energy), those that were physically closer together (less tracking time), and those without the shell (less processing) . time) before smaller, more distant or “in shell” nuts. This suggests that at least some animals can remember and use optimal foraging variables even when food is distant and beyond the range of immediate perception. Both studies support important predictions of OFT.
If one could estimate the variables important to foraging, one could potentially predict the diet of certain hominids that lived in the distant past. It’s a daunting undertaking, but this business of human evolution was never meant to be easy. The OFT approach forces researchers to learn how and why animals use specific resources, leading to more thorough considerations of early hominid ecology. A few scientists have used OFT with success, particularly in the archaeological treatment of comparatively young hominids such as Neanderthals and anatomically modern humans.
But a few brave souls have delved into the more distant history of human nutrition. For example, one team used OFT, modern analogue habitats, and evidence from the fossil record to estimate predicted optimal diets Australopithecus boisei. This is the famous “Nutcracker Man” who lived in East Africa almost 2 million years ago. The research suggests a wide range of potential food sources, widely differing movement patterns – based on characteristics such as habitat or use of digging sticks – and the seasonal importance of certain resources such as roots and tubers in meeting estimated calorie needs.
Researchers Tom Hatley and John Kappelman found in 1980 that hominids have bunodonts — low, rounded-cusped rear teeth — that share many similarities with bears and pigs. If you’ve watched these animals forage, you know they eat almost anything: tubers, fruit, foliage and twigs, invertebrates, honey, and vertebrates, whether preyed or hunted. The percentage contribution of each food type to the diet depends (you guessed it) on the energetic value of certain foods in certain habitats and times of the year. Evidence from throughout human evolution suggests that our ancestors, and even us as modern humans, were omnivores as well.
And the notion that our ancient ancestors were great hunters is probably wrong, since—at least before the advance of sophisticated knowledge and technology—bipeds are an extremely poor way of hunting game. Our mobility is restricted even more than with bears and pigs. Anthropologist Bruce Latimer has pointed out that the fastest human on the planet cannot catch up with the average rabbit. Another reason to be opportunistic when eating.
Simple characterizations of hominid ecology are divorced from the actual and wondrous complexity of our shared history. The recent incorporation of pastoral and agricultural products into many modern human diets—for which we have rapidly developed physiological adaptations—is but an extension of an ancient imperative. Hominids didn’t spread first across Africa and then across the globe using just one dietary strategy or sticking to a precise mix of carbohydrates, proteins, and fats. We made it by being very flexible both socially and environmentally, always looking for the greener grass (metaphorically) or riper fruit (literally).
Ken Sayers, postdoctoral researcher in primate and human evolution, Georgia State University
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