This would have increased the range of foods they could eat, because many foods are indigestible or poisonous until cooked. Cooking would also have reduced the time they spent chewing and digesting their food. Use of fire may have had other important consequences. For example, cooking reduced the digestive work required of the gut, so the gut shrank (and, yes, there is fossil evidence for this), releasing some of the metabolic energy needed to run larger brains. As yet, this interesting hypothesis remains unproven, because good evidence for systematic control of fire appears only from about
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