Cells copy their genetic material, made up of DNA and RNA, to pass it on to new generations. Although DNA is the form of genetic material that most living organisms use today, some scientists believe that RNA was the first information storage molecule on early Earth because it can make copies of itself.
Because some modern viruses use RNA to store genetic information, some scientists believe that viruses could have evolved from self-replicating RNA. This possibility would mean that viruses may have appeared before bacteria. But because viruses don’t leave fossils behind, no evidence is available to support this idea.
At some point, metabolic reactions and replication processes had to come together within a membrane to form an early form of cell: a precell. Perhaps this happened when a virus-like structure infected a collection of metabolic reactions enclosed within a membrane. The precell could then duplicate, leading to the evolution of the first living cell. This cell would have been like today’s bacteria and archaea.
Perhaps virus-like structures formed before cells. However, those simple virus-like structures have only been fragments of DNA or RNA, so could they really be considered “viruses”?
Another popular theory states that viruses evolved from degenerate bacteria or archaea that lost most of the genetic instructions for carrying out metabolism and forming cells. there is many examples of smaller similar degeneracies that have occurred in the bacterial world today.