Non-cellular life

[3][4][5] Researchers initially described viruses as "poisons" or "toxins", then as "infectious proteins"; but they possess genetic material, a defined structure, and the ability to spontaneously assemble from their constituent parts.

Viroids are some of the smallest infectious agents, consisting solely of short strands of circular, single-stranded RNA without protein coats.

[12] A possible explanation of the origin of viroids sees them as "living relics" from a hypothetical, ancient, and non-cellular RNA world before the evolution of DNA or of protein.

[13][14] This view, first proposed in the 1980s,[13] regained popularity in the 2010s to explain crucial intermediate steps in the evolution of life from inanimate matter (abiogenesis).

They differ from viroids in that they code for two distinct proteins, dubbed "oblins", and for the predicted rod-like secondary structure of their RNA.