The Evolution of Viruses - Zhdanov V. M. 1990

Special Section

This section of the book attempts to examine the potential origins and evolutionary pathways of various virus groups within the families and genera recognized by the international Virus Classification. However, this principle is not strictly maintained throughout. First, evolutionary connections between Viruses from different families have been established with near certainty in some cases (e.g., the families Hepadnaviridae and Caulimoviridae, or Togaviridae and Tobamoviridae). In other instances, viruses that only recently appeared to be evolutionarily close (such as the genera Togaviridae and Flavivirus) have turned out to belong to different families, with an evolutionary relationship that is either distant or doubtful at best. We have also altered the presentation order for the evolution of specific virus groups compared to the international classification [Matthews R., 1982], which begins with the most complex Introduction/6.html">DNA-containing viruses and ends with multipartite RNA-containing Viruses. For this book, we deemed it appropriate to adopt the reverse sequence, starting with Prions, Viroids, and Plasmids and concluding with Poxviruses. This is because the evolutionary path traversed by plasmids, for instance, is undoubtedly shorter than that of poxviruses—referring not necessarily to the time span of their existence (although this is likely true in this case as well), but to the substance of the Evolutionary Processes that took place.

The Structure/133.html">Discussion on evolution is preceded by a concise Overview of the respective viruses, kept to a minimum to remind the reader of the key characteristics of their genome, Proteins, virion structure, and Replication strategy, as well as information on their ecological niches. More detailed ecological data, alongside insights into virus Structure and function, are addressed in the sections dedicated to their evolutionary pathways.

Unfortunately, hypotheses regarding THE ORIGIN OF various virus groups—with the possible exception of the simplest autonomous genetic structures—remain rather speculative and general. Nevertheless, we believe it useful to present these general considerations, bearing in mind that back in the 1940s and 1950s, the earliest virus classifications, however naive and uninformed they might seem, nonetheless proved valuable by stimulating further research in this field.