Viral Analogy
RNA viruses may seem something of a model for the RNA-world scenario, but the analogy is inapt, because a virus can’t replicate itself; the very thing that the RNA-world scenario aims to explain.
Retroviruses pack a tiny genome encoded in RNA. A retrovirus hijacks a host cell for replication, copying its RNA into the cell’s DNA using a reverse transcriptase enzyme. The host then duplicates, with the retrovirus genetic instructions intact.
A virus works from DNA for copying itself but bundles itself up for inheritance using RNA to transmit the hereditary data. Thus, today’s viruses are much too sophisticated, and yet not sufficiently self-sustaining, to aid in understanding how RNA replication arose.
A less obvious disadvantage to RNA life becomes apparent by comparing RNA to DNA. DNA is a richer storage medium. A retrovirus is about as complex as an RNA-encoded entity can be.
