Compare the three hypotheses that explain the evolution of viruses

CONCEPTS TO CONSIDER : According to the progressive, or escape, hypothesis , viruses may have originated as mobile genetic elements that could have escaped and moved from one cell and entered another through damaged cell membranes. Viruses may trace their origin to animal cells, plant cells, bacterial cells, or archaeal cells. The regressive, or reduction, hypothesis asserts that viruses are remnants of cellular organisms; they evolved from free-living, complex cellular ancestors. As they became parasitic, the viruses gradually lost some of the genes necessary for protein synthesis. Genes they no longer needed, like those for protein synthesis, were gradually lost through evolution. According to the virus-first hypothesis , viruses predate or coevolved with their current cellular hosts. Viruses may have initially existed as self-replicating units. As they evolved, viruses produced enzymes for the synthesis of membranes and cell walls, leading to the formation of the first cells.