An age ago—perhaps as long as 20,000 years—small bands of hardy people, ancestors of the adventurers who had crossed the Arctic land bridge from Siberia thousands of years earlier, were hunting and foraging in what is now the Valley of Oaxaca. The forests and meadows abounded with edible plants and game—from squirrels and rabbits to great Ice Age herds of camels, horses, and mammoths. Supplied with abundant food, the people multiplied.

But by around 7000 B.C. the climate had warmed several degrees, and the great game animals were extinct. Perhaps in response, the people began to sow seeds of their favorite edible wild grains, legumes, vegetables, and fruits. As their descendants still do today, those ancient Oaxacans picked out the biggest and healthiest seeds to plant for the succeeding year’s crop. After many generations, their fields were blooming with domesticated beans, squash, corn, and avocados nearly as robust as those enjoyed today.