Potatoes, sweet potatoes, yams, cassava these roots and tubers are staple foods for billions of people. They are subterrancan organs in which plants store starch, large molecular aggregates of the sugars they createduring photosynthesis. They are herefore a concentrated and long-lived package of nourishment for us as well. Some anthropologists theorize that roots and tubers may have helped fuel human evolution, when the climate of the African savanna cooled about 2 million years ago and fruits becam scarce. Because tubers were plentiful and far moro nutritious when cooked-raw starch granules resist our digestive enzymes, while gelated starch does not they may have offered a significant advantage to early humans who learned to dig for them and roast them in the embers of a fire