“Survival of the fittest” is one of the central notions of Darwinian evolution. But how collections of molecules came to behave in a Darwinian fashion remains a mystery. Now, Katarzyna Adamala and Jack W. Szostak of Harvard University have shed light on the role catalysts may have played (Nat. Chem. 2013, DOI: 10.1038/nchem.1650). The pair enclosed a catalytic peptide inside fatty acid vesicles to make partial mimics of primitive cells. They then mixed these vesicles with vesicles lacking the catalyst and compared the vesicles’ growth. The catalyst-containing vesicles grew more efficiently, sometimes even at the expense of their neighbors. That’s because the catalyst generates a hydrophobic peptide product that makes fatty acids accumulate more efficiently in vesicle membranes. This system can’t yet evolve because the catalyst can’t be passed from one generation of cells to the next, Szostak says. In the future, however, it might be possible to achieve evolution in the lab by loading vesicles with a ribozyme catalyst that is heritable.