Whereas viruses have one of at least 7 different types of genetic information, namely dsDNA, ssDNA, dsRNA, ssRNA+, ssRNA-, ssRNA-RT, dsDNA-RT.
Moreover, in contrast to cellular organisms, viruses don't have universally conserved sequences in their genomes to be compared by.
Smallest viruses may consist of only from 1–2 kb genome coding for 1 or 2 genes and it is enough for them to successfully evolve and travel through space and time by infecting and replicating (make copies of their own) in its host.
[10] The function of the vast majority of viral genes remain unknown und the approaches to study have to be developed.
[13] Members of viral families like Rhabdoviridae infect hosts from different kingdoms e.g. plants and vertebrates.
[14] And members of genera Psimunavirus and Myohalovirus infect hosts from different domains of life e.g. bacteria and archaea.
[citation needed] Viral evolution or evolution of viruses presumably started from the beginning of the second age of RNA world, when different types of viral genomes arose through the transition from RNA- RT –DNA, which also emphasises that viruses played a critical role in the emergence of DNA and predate LUCA [18][19] The abundance and variety of viral genes also imply that their origin predates LUCA.
[21][22] Virus evolution is more complex as it is highly prone to horizontal gene transfer, genetic recombination and reassortment.
[23][24] Viruses are capable of infecting all organisms on earth and they are able to survive in much harsher environments, than any cellular life form.
As viruses can not be included in the tree of life there is no separate structure illustrating viral diversity and evolutionary relationships.
The vast majority of the sequences from any environment, both from wild nature and human made, reservoirs are new.