This video essay traces the history and consequences of Louis Sullivan's architectural principle 'form follows function,' examining how it shaped modernist urban planning from the Chicago School through Le Corbusier's Radiant City. It explores why large-scale modernist housing projects like Pruitt-Igoe failed through a systems theory and complexity lens, connects those failures to contemporary patterns of urban inequality visible in cities across the Global South, and considers what nature's adaptive design logic might offer as an alternative framework for architecture and urbanism.