Evolution is complexity, analogically, optimally realised. Leonardo da Vinci's Golden Ratio links the Asynsis principle with the Constructal law, a classical theory of everything revealing nature's inherent economy, elegance and beauty, its inherent sustainability. A new optimising, geometric design law of nature in the Asynsis principle-Constructal law, a new paradigm that will serve to promote in enviro-extremis, the global sustainable design and development agenda, is also a paradigm for how cities evolve to facilitate more fluid and enhanced volumes of energy/matter/information resource flow. This dynamical symmetrical behaviour is a temporal signature of energy, mass and information flow, of nature self-organising itself more easily over time, for less energy cost. The reason we see the ratio in statics so often is because it is an archetypal, emergent dynamical signature, a static condensate revealing the optimal dynamical geometries in natural flow systems. So one could argue that to best preserve nature - we had also best (& urgently), emulate her - by building these behaviours into our city metabolisms and morphologies. The arguments for green building and city planning just got far more compelling as a result (because to be "green" is actually following a law of nature, the fundamental geometry of which is also an icon of art, design and architecture). But will it make our jobs as designers easier (as Einstein remarked to Corb regarding his Modulor), or harder (since we are dealing with a process, not a state - a function, not a form)? Fortunately, these behaviours also access mathematical singularities when pushed far from equilibrium (the so-called "edge of (deterministic) chaos"), so they represent the emergence of infinite formal creativity as well. My suggested argument is that "Form fulfils Function" in that emergent, contingent designed forms (including culturally designed artifacts of all scales, from jewelry to cities), must and should arise from a contingent world - but that it is critical that the functions that those forms house also emulate nature's laws and must be optimal, especially in their use of energy, matter and information. This is therefore also not an argument for only employing flowing organic lines in the forms of all designed artifacts, which is biomimicry as pastiche of the laws of physics and thermodynamics. Organic forms should fulfill organic functions, otherwise they're just Las Vegas trompe l'oeil. This is where contingency allows us to express a universe of formal possibilities, restricted only by our imaginations, budgets and those same natural laws. So to move from sustainable to evolvable (and back), in a virtuous circular feedback loop, we need to fully comprehend and apply the new classical theory of everything, the Asynsis principle-Constructal law http://asynsis.wordpress.com http://www.facebook.com/pages/Asynsis/134142719983026 http://www.facebook.com/AsynsisSustopiaInitiative http://www.facebook.com/ADbooks