Origins of Life: Emergence of the RNA World

Abstract The RNA World hypothesis refers to a period during the evolution of life on Earth, preceding the DNA/RNA/protein‐based systems of modern biology, during which RNA alone directed and catalyzed the chemistry of life. The concept is an elegant solution to the problem of devolving our intertwined 3‐biopolymer biochemistry toward its origins as the simplest system imaginable. In support of this idea, a scattering of molecular clues within our cells point suggestively toward an RNA‐only period leading up to the ribozyme‐mediated invention of protein synthesis. Indeed, the RNA World hypothesis is a very sensible scenario when considered from the perspective of trying to simplify life's complexity. The alternative perspective, however, imagining a sterile, primordial Earth and trying to assemble abiotically produced precursors into the RNA World is an extremely difficult problem. Certain steps along the logical chemical pathway to the RNA World have been demonstrated in the laboratory, but many others remain problematic. The exploration of RNA's catalytic properties has been encouraging, but complex ribozymes are extremely scarce in RNA populations. If the RNA World did once exist, it came about by a mechanism that has not yet been adequately elucidated, including the possibility that a different, unknown, biopolymer system may have preceded the RNA World.