A symbiotic origin of the ribosome?

The origin of life is one of the great mysteries of science. Of the multiple unsolved problems, the origin of the translation system (the means by which the genetic code inscribed on chromosomes is converted into reliable protein sequences) remains the most enigmatic. A resolution of this problem is unlikely to be advanced by focusing on the features of the complex system found in today's species, as the reliable production of complex proteins could not possibly have been the function of the earliest ribosome. Although exact answers may be beyond reach, we propose that the protoribosome was a parasite that through mutually constrained coevolution with the host eventually led to the emergence of a molecular machine no longer reflecting its simpler beginnings. If this view is correct, then like the spliceosome and perhaps the mitochondrion in the stem eukaryote, a repurposed host-parasite interaction led to a dramatic change in cell biology at the base of the tree of life, in this case leading to the exit from a largely RNA world.