What better subject for the first chapter than the food with which we all begin our lives? Humans are mammals, a word that means “creatures of the breast,” and the first food that any mammal tastes is milk. Milk is food for the beginning eater, a gulpable essence distilled by the mother from her own more variable and challenging diet. When our ancestors took up dairying, they adopted the cow, the ewe, and the goat as surrogate mothers. These creatures accomplish the miracle of turning meadow and hay into buckets of human nourishment. And their milk turned out to be an elemental fluid rich in possibility, just a step or two away from luxurious cream, fragrant golden butter, and a multitude of flavorful foods concocted by friendly microbes.