Viruses did not evolve first, they found. Instead, viruses and bacteria both descended from an ancient cellular life form. But while – like humans – bacteria evolved to become more complex, viruses became simpler. Today, viruses are so small and simple, they can’t even replicate on their own.

The eukaryotic ssDNA viruses apparently evolved via a fusion of genes from prokaryotic rolling circle-replicating plasmids and positive-strand RNA viruses. Different families of eukaryotic dsDNA viruses appear to have originated from specific groups of bacteriophages on at least two independent occasions.

Prokaryotic and Eukaryotic cells are both alive, while viruses are not. Viruses have very few organelles, similar to the prokaryotic cells. They contain a plasma membrane, cell wall, RNA or DNA, and a protein capsule.

Virus-first hypothesis: Viruses evolved from complex molecules of protein and nucleic acid before cells first appeared on earth. By this hypothesis, viruses contributed to the rise of cellular life. This is supported by the idea that all viral genomes encode proteins that do not have cellular homologs.

Smallpox and measles viruses are among the oldest that infect humans. Having evolved from viruses that infected other animals, they first appeared in humans in Europe and North Africa thousands of years ago.

Martinus Beijerinck is often called the Father of Virology.

In 1892, Dmitri Ivanovsky used one of these filters to show that sap from a diseased tobacco plant remained infectious to healthy tobacco plants despite having been filtered. Martinus Beijerinck called the filtered, infectious substance a “virus” and this discovery is considered to be the beginning of virology.

Difference Between DNA & RNA Viruses The viruses that contain DNA as their genetic material are called the DNA viruses. RNA viruses, on the other hand, contain RNA as their genetic material. DNA viruses are mostly double-stranded while RNA viruses are single-stranded.

RNA viruses like poliovirus likely have higher mutation rates than what would be optimal for the organism because higher mutation rates are, in part, a byproduct of selection for faster genomic replication.

RNA viruses generally have very high mutation rates compared to DNA viruses, because viral RNA polymerases lack the proofreading ability of DNA polymerases. The genetic diversity of RNA viruses is one reason why it is difficult to make effective vaccines against them.

RNA viruses have high mutation rates that allow especially fast evolution. An example is the evolution of drug resistance in HIV.

1.1. RNA Viruses. Human diseases causing RNA viruses include Orthomyxoviruses, Hepatitis C Virus (HCV), Ebola disease, SARS, influenza, polio measles and retrovirus including adult Human T-cell lymphotropic virus type 1 (HTLV-1) and human immunodeficiency virus (HIV).

Nucleic acids are involved in the preservation, replication, and expression of hereditary information. Two major types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).