All modern organisms have DNA as a store of genetic information, RNA as a message and Proteins as their major cellular catalyst. This is very complicated model and when we think of the origins of life we ask how did it all start? Where did DNA come from as Proteins are involved in its replication? But DNA codes for Proteins? What came first Polynucleotides or Polypeptides?
The RNA world is the believed hypothesis in modern genetics, that answers these questions. RNA led to Proteins which led to DNA.
Evidence supporting the RNA world
RNA can behave as both a store of genetic information and as a cellular catalyst.