viruses from bacteria through so-called “regressive” evolution. Most
recognized is the third hypothesis that the viruses originate from cellular
components similar to plasmids. Once appeared they have evolved from
simple to more complexly organized forms, and some of them could have a
polyphiletic way of evolving thus creating the enormous “Vira Kingdom”.
image
Figure 2–90. Electron micrograph of DNA T2 phage released from the phage head under the action of osmotic shock (After Kleinschmidt et al., 1962).
The behaviour of viruses as “terminators” of the living cells and
organisms and the absence of own, independent metabolism, do not give
grounds to be considered cells, even less adequate ones. Their biological
role and the causes for their arising are to be elucidated.