Homochirality—the predominance of single enantiomers, such as l-amino acids—is a key property of biomolecules in living systems. The mechanism by which it evolved is unknown, but a new model for the evolution of biological homochirality has been developed by Donna G. Blackmond of Imperial College, London, and coworkers (Nature 2006, 441, 621). They show that amino acid-catalyzed aldol reactions in which solid- and solution-phase amino acid enantiomers exist in equilibrium provide an efficient mechanism for asymmetric amplification of single-enantiomer products. Serine provides the most significant amplification. Previous proposals for the origin of homochirality have involved far-from-equilibrium systems. The new mechanism involves an equilibrium process that "can operate in aqueous systems, making it an appealing proposition for explaining ... the development of high enantiomeric excess in biomolecules from a presumably racemic prebiotic world," the researchers write. They plan to report having observed the effect with other types of chiral catalysts as well, suggesting that it could have important implications for asymmetric catalysis in general.