On Food and Cooking

these roots and tubers are staple foods for
billions of people. They are subterranean
organs in which plants store starch, large
molecular aggregates of the sugars they create
during photosynthesis. They are therefore 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 became
scarce. Because tubers were plentiful and far
more 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.
Though some underground vegetables are a
third or more starch by weight, many others
— carrots, turnips, beets — contain little or
no starch. Because starch granules absorb