Our earliest human ancestors were omnivores: they ate whatever they could find worth eating on the African savanna, from meat scraps on an animal carcass to nuts, fruits, leaves, and tubers. They relied on taste and smell to judge whether a new object was edible—sweetness meant nourishing sugars, bitterness toxic alkaloids, foulness dangerous decay—and to help identify and recall the effects of objects they had encountered before. And they ate a varied diet that probably included several hundred different kinds of foods. They had a lot of flavors to keep track of.