Amino acids, the building blocks of the cell's protein factory, occur in only 20 different types in mammalian proteins, yet from these 20 simple molecules an almost infinite variety of structural proteins and enzymes can be built, and they can catalyze chemical processes far more efficiently and selectively than our chemical efforts. The natural amino acids are also remarkable in that they all are constructed by nature in the l form in proteins. What event early in the history of life on Earth led to the chirality of amino acids is a question that has always intrigued me. It may be that catalysis on a primitive inorganic surface favored the l form over the d, or the selection of l amino acids could have been an effect of polarized light