RNA may have predated deoxyribonucleic acid (DNA) in our evolution. It is a reasonable information medium, and also is protean enough to make enzymes.
DNA is more stable than RNA because the phosphodiester bonds in RNA are attacked by its extra OH groups. In living organisms and some viruses DNA is double-stranded (and, more rarely, so is RNA), which helps protect the organic bases from chemical attack. In addition, some cells have error-correcting mechanisms.
- RNA - Ribose nucleic acid
- DNA - Deoxyribose nucleic acid
DNA and the mechanisms surrounding it are a data storage medium of phenomenal reliability by the standards of anything we build. Nevertheless, over long periods of time many small changes have occurred. Most of these are neutral - if proteins result from that section of genetic material, the change is in a region that makes no difference - serum albumin for instance shows mutations at what is probably close to the basal rate. Some completely alter the protein - frame-shifting mutations for instance - and others slightly alter it leaving it workable but with different characteristics. Mutations add new sections to the library from which natural selection drives evolution.
Changes in the DNA coding for switches and other control mechanisms, which are currently incompletely understood, have the possibility of creating very significant changes, but conversely will commonly produce disaster, and the previous values therefore be highly conserved.