Today I stepped outside to find my 18-month-old daughter arduously ascending the board-and-nail rung ladder on the mulberry tree next to the garden, all the while chanting her new favorite word, "Up. Up. Up." As I tore across the yard to spot her, my mind a-whirl with competing terror and admiration, I had to wonder. If she's determined to climb six feet up a tree trunk at this age, what heights might she attempt in the future?