Strip a ring of bark from most trees and you have killed them. The bark is where sugar travels down from the leaves, and a tree cut off at the waist starves slowly, standing up; farmers used to clear land that way. The African baobab is an exception. People have stripped its bark for rope for generations, and in a dry season elephants gouge it for the wet wood underneath, and the tree, within limits, grows a new layer over the wound and carries on. Baobabs in elephant country wear the scars, lumpy and folded like a badly healed knee. They aren’t invulnerable: when drought, fire and elephants come at once, they die like anything else. But they have lasted a long time by not keeping the part they can’t afford to lose on the outside, where everything can reach it. A good deal of what gets built, by trees and otherwise, does exactly the opposite.