The evolution of multicellularity set the stage for an incredible increase in the diversity and complexity of life on Earth. The increase in biological complexity associated with multi-cellularity required parallel innovation in the mechanical properties of multi-cellular bodies. Though a cursory review of any multi-cellular organism provides an appreciation of this intertwining of biological and mechanical complexity, little is known about how such mechanical properties may have evolved. We hypothesize that prior to the evolution of genetically-regulated development, physics played a key role in initiating simple multi-cellular development. Through a combination of experimental evolution (which permits observation of the evolution of multi-cellularity in the lab, as it occurs), and the tools of soft matter (microscopy, mechanical testing, and more), we show that physics likely played a fundamental role in the evolution of complex multi-cellularity.