This article reviews efforts to explain why certain biological molecules tend to be all right-handed (e.g., sugars) or left-handed (e.g., amino acids). An explanation might lie in the evolution of enzymes involved in their synthesis. For example, the fact that some organisms produce predominantly d-alanine could be explained by random mutations for the opposite enzyme rather than a modification of some physical molecular-pairing mechanism.

John E. Morris
Corvallis, Ore.