Viral Evolution - Three Theories of Evolution

Three Theories of Evolution

According to the progressive theory, segments of DNA escaped from existing cells, mutated and eventually evolved into modern viruses. Existing mobile genes such as plasmids and transposons support this theory.

The regressive theory postulates that viruses are "devolved" bacteria. Stemming from obligate intracellular parasites such as Chlamydia, viruses would have lost a large portion of their genetic code. This theory seems to best describe large double stranded DNA viruses such smallpox.

Based on the RNA world theory of life, the Virus First hypothesis proposes that viruses evolved from the very first segments of RNA, predating the early cells.

Read more about this topic:  Viral Evolution

Famous quotes containing the words theories and/or evolution:

    The real trouble about women is that they must always go on trying to adapt themselves to men’s theories of women, as they always have done. When a woman is thoroughly herself, she is being what her type of man wants her to be. When a woman is hysterical it’s because she doesn’t quite know what to be, which pattern to follow, which man’s picture of woman to live up to.
    —D.H. (David Herbert)

    The more specific idea of evolution now reached is—a change from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity, accompanying the dissipation of motion and integration of matter.
    Herbert Spencer (1820–1903)