Mobile technology has transformed the way we live — how we read, work, communicate, shop and date. But we already know this. What we have not yet grasped is the way the tiny machines in front of us are remolding our skeletons, possibly altering not just the behaviors we exhibit but the bodies we inhabit. New research in biomechanics suggests that young people are developing hornlike spikes at the back of their skulls — bone spurs caused by the forward tilt of the head, which shifts weight from the spine to the muscles at the back of the head, causing...