Experimental RNA evolution

The recent ability to select functional RNA molecules through combinatorial chemistry has ignited exobiological research by offering a set of tools fo r testing early theories of RNA evolution without the need for organisms. T his process can retrieve molecules present in as few as one in 1 x 10(15) s equences, which suggests that careful design may allow 'resuscitation' of a ctive RNA molecules that have been 'extinct' for over three billion years, if they ever 'lived' at all. These experiments now provide a wonderful sett ing for exploring the basic process of evolution at its most fundamental le vel - a single molecule - as well as providing a window onto the set of bui lding blocks and constraints that would have defined many events in prebiot ic evolution.