Alternative bases or nucleosides with alternative bases were prebiotically available for incorporation into life.
Canonical bases may have been higher in abundance relative to non-canonical bases.
Non-canonical bases structurally mimic RNA properties with canonical bases.
Non-canonical bases warp RNA structure and interrupt central RNA interactions.
Non-canonical bases are part of the modern RNA repertoire.
Genetic makeup from the time before the first cellular life to now only shows compatibility with the canonical bases.