Following the park guide, I scribbled notes as he taught about the plants of the Bahamian primeval forest. He told us which trees to avoid. The Poison wood tree, he said, secretes a black sap that causes a painful, itchy rash. But not to worry! The antidote could usually be found growing right next it. “Cut into the red bark of the Gum Elemi tree,” he said, “and rub the sap on the rash. It will immediately begin to heal.”

I nearly dropped my pencil in astonishment. I hadn’t expected to find a picture of salvation in the forest. But in…