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Research Projects
Tubers and Cooking in Human Evolution
| Cooking may have adaptive advantages, such as the detoxification and tenderization of meat and marginal plant foods. Some authors suggest that cooking evolved as early as 2.0 million years ago, facilitating the emergence and spread of Homo erectus. One aspect of this hypothesis suggests that roasting tubers was important because tubers are a critical food resource for hunter-gatherers and fire is expected to ease chewing effort and improve digestibility. To examine this hypothesis, we initiated a study of Hadza cooking behavior. The Hadza are a population of hunter-gatherers living around the southern shores of Lake Eyasi, Tanzania. They derive 30-40% of their daily Kcal from tubers, which they tend to roast on open fires (Figure 1). |
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Figure 1. The roasting and preparation of tubers |
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The objectives of our study are twofold. First, we aim to characterize Hadza roasting behavior (Figure 2). Second, we aim to characterize the effects of roasting on the mechanical properties and starch content of tubers (Figure 3). Starch is a complex and important carbohydrate in the human diet, and roasting may improve the extent to which it is digested in the mouth and small intestine. To better understand the evolution of starch digestion, our lab has also initiated a study of the salivary amylase gene (AMY1), the enzyme responsible for hydrolyzing starch into glucose (for more details, click here).
Our initial results indicate that roasting exerts a significant effect on the material properties of tubers. After just 90 sec on an open fire the elastic modulus and fracture toughness of a tuber are substantially lower, but more data are needed to determine if the extent of such changes is common across edible tubers. Stay tuned! |
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| Figure 2. PhD student Justin Yeakel using an infrared pyrometer to measure the temperature of a fire used to roast tubers. The temperature ranged from 700-900°C. |
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Figure 3. Cross-sectional images of a raw and cooked tuber called do'aiko (Vigna macrorhyncha; Fabaceae). After 90 sec of roasting, the fracture toughness changed substantially. The tough cortical cells surrounding the tuber also changed: 1753 to 807 J m-2 . |
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