Fact and assumption in studies on the origins of life.

Proteins and nucleic acids organise metabolic systems very efficiently. Original forms of life may have depended on less efficient mechanisms which have been superseded in the course of evolutionary selection. Discussion and experiment on the origins of life should therefore not depend on the assumption that substances and mechanisms, now seemingly essential, were essential initially. Instead we should consider what might happen in a few million years on moist mineral surfaces, smeared with bituminous material, and exposed to UV light in a reducing atmosphere in the absence of predators. What little evidence can be gathered from differences in composition and metabolic behaviour between ancient and recently evolved species suggests that the trend in biochemical evolution is towards simplification.