"“The great irony is that in the beginning, the gut was all there was. “We’re basically a highly evolved earthwork surrounding the intestinal tract,” Khoruts commented as we drove away from his clinic the last day I was there. Eventually, the food processor had to have a brain attached to help it look for food, and limbs to reach that food. That increased its size, so it needed a circulatory system to distributed the fuel that powered the limbs. And so on. Even now, the digestive tract has its own immune system and its own primitive brain, the so-called enteric nervous system. I recalled what Ton van Vliet had said at one point in our conversation: “People are surprised to learn: They are a big pipe with a little bit around it.”"