Then along came RNA editing, in which guide RNAs or enzyme action modify some messenger RNAs such that the final protein sequence cannot be deduced from the gene sequence alone.

Such small antisense RNAs may later have gained a role in RNA editing, possibly under selective pressure to repair a region or restore a reading frame after loss or erosion of a module.

The molecular mechanism and physiological function of recoding by A-to-I RNA editing is well known, but its evolutionary significance remains a mystery.