Evolution trains a from-scratch catalyst Metal-bound peptides can catalyze simple reactions such as ester hydrolysis and may have been the starting point for the evolution of modern enzymes. Studer et al. selected progressively more-proficient variants of a small protein derived from a computationally designed zinc-binding peptide. The resulting enzyme could perform the trained reaction at rates typical for naturally evolved enzymes and serendipitously developed a strong preference for a single enantiomer of the substrate. A structure of the final catalyst highlights how small, progressive changes can remodel both catalytic residues and protein architecture in unpredictable ways. Science , this issue p. 1285