Final answer:
There are three main hypotheses about the origins of viral genomes: the devolution hypothesis where viruses evolved from free-living cells, the escapist hypothesis where they originated from RNA and DNA molecules, and the virus first hypothesis which suggests viruses were one of the first self-replicating entities.
Step-by-step explanation:
The question pertains to the candidates for the original sources of viral genomes. Scientists are probing into the evolutionary history of viruses, which is particularly challenging because unlike other organisms, viruses leave no fossil evidence. Viral genomes are often found integrated in the host genome, and this can help to construct their evolutionary pathway. There are several hypotheses regarding the origin of viruses:
- The devolution or regressive hypothesis posits that viruses evolved from free-living cells or intracellular parasites.
- The escapist or progressive hypothesis suggests that viruses originated from self-replicating RNA and DNA molecules that escaped from host cells.
- The virus first hypothesis implies that viruses may predate the first cells, suggesting they were among the first self-replicating entities.
Further understanding is expected to emerge from the field of virus molecular systematics, which compares sequenced genetic material to hypothesize about virus origins.