One summer morning almost 30 years ago, my uncle Grainger Hunt phoned to say that a young bald eagle he had been watching on the Salt River in Arizona had begun its adolescent migration. The bird had been fitted with a small radio beacon that beeped every second or so, and my uncle owned a Cessna 182 with radio receivers mounted on each wing to track the bird. So I caught a jet to Phoenix and climbed aboard the Cessna, hoping that the young eagle would lead us to some unknown fly-fishing spot, and I would sell the adventure story to Sports Illustrated.The trip felt elemental: learning from my uncle how to track an animal—even if our quarry wore a radio tag, we were in an airplane, and our goal was to learn more about the national bird to keep it safe. As we flew, we talked about birds of prey and predators in general. Grainger was a hunter, a forager of wild food, and he earned his doctorate in evolutionary biology. He pointed out that we are predators: our eyes are in front, our front teeth are sharp, and our hands and arms evolved to throw a rock or a spear or a 100-mile-per-hour fastball. We coexiste …