Over 200 years after Coulomb's studies(1), a general connection between the mechanical response of a granular material and the constituents' shape remains unknown(2-10). The key difficulty in articulating this relationship is that shape is an inexhaustible parameter, making its systematic exploration infeasible. Here we show that the role of particle shape can, however, be explored efficiently when granular design is viewed in the context of artificial evolution(11). By introducing a mutable representation for particle shapes, we demonstrate with computer simulation how shapes can be evolved. As proof of principle, we predicted motifs that link shape to packing stiffness, discovered a particle that produces aggregates that stiffen-rather than weaken-under compression, and verified the results using three-dimensional printing. More generally, our approach facilitates the exploration of the role of arbitrary particle geometry in jammed systems, and invites the discovery and design of granular matter with optimized properties.