To cross the bridge over the narrow, swift waters of the Iowa River is to enter a new and unexpected realm. Here, in the Driftless region of Wisconsin, so-called because glaciers were unable to push piles of gravelly drift through the hills, the terrain is sloping, craggy, forested, alien to the monolithic Iowan corn fields that I have left behind. With the afternoon slipping into thick mist, I reach a cluster of houses and a scruffy clearing in the embrace of silent woods. Two pigs root about in an area fenced off by live wire; chickens squawk from a nearby enclosure. When I exit the rental car, a lean black dog lunges at me, nipping my hands and feet, testing my nerves. For the past year, I have circumnavigated the world, researching the history of the human diet on a shoestring budget, often crashing at the homes of friends and strangers. Such visits sometimes yield unexpected insights into the history of food and health. More to the point, though, I am hungry and broke, so I fend off the vicious mutt and ask for directions at the nearest dwelling.
With the canine hassling me like the neighborhood thug, I hurriedly make my way along an overgrown trail. At the end of the path, I call out greetings through a screen door. "Ah, you finally made it!" replies Tom, an easygoing chap with matted locks whom I had met over the Internet. Next to him on the couch are a brunette wrapped in a towel and a dreadlocked African American in tattered overalls. All three are giggling over an astrology text. They ask for my sign and then laugh some more. Two naked boys with...