Across thousands of years of sediment, ancient shells have preserved a rhythm that challenges what science thought it understood about life's most fundamental instructions. Paleontologists have found that entire populations of marine organisms periodically reversed the direction of their spirals — clockwise to counterclockwise and back — in a pattern too consistent and too regular to be chance. The discovery sits at the edge of what current evolutionary and developmental biology can explain, suggesting that the deep processes shaping living forms may be far more responsive to the world around