At the dawn of the twentieth century, the soybean was little more than a botanical curiosity beyond East Asia. Today, soy is planted on hundreds of millions of acres of farmland across multiple continents, it is a leading export of emerging and developed economies like those of Brazil and the United States, and is the third-most valuable crop in the world behind only rice and wheat. Yet throughout the historical spread of soybean cultivation, the value of soy was often far from self-evident, both to its potential consumers and to the farmers who came to grow the crop. The rapid expansion...