retroviruses; mammals

Don McAllister mcall at SUPERAJE.COM
Wed Sep 29 14:25:52 CDT 1999

Ken Kinman wrote:

>      I don't know a whole lot about viruses either,

Nor I.  But in Margulis and Schwartz's Five Kingdoms they state:

Viruses are probably related more closely to their hosts than to each other.
They may have originated as nucleic acids that escaped from cells and began
replicating on their own -- always, of course by returning to use the complex
chemicals and structures in their former home cells.  Thus the polio and flu
viruses are probably more related to people, and the tobacco mosaic virus (TMV)
to tobacco, than polio and TMV are to each other."

There are some who would go so far as to say that viruses are not living beings
- basically because they are inert outside of a living cell.  But a number of
organisms, including bacteria or fungi are inert outside of cells, or more
broadly outside of their particular habitat.  Parasites and disease organisms
often undergo simplification when the host assumes protectivie and nutritive

Virus commonalities are, according to a textbook in hand:
1. Contain a single type of nucleic acid, either DNA or RNA
2. Contain a protein coat that surrounds the nucleic acid
3. Multiply inside living cells using the synthesizing machinery of the cell
4. Cause the synthesis of specialized structures that can transfer the viral
nucleic acid to other cells.

Of course the opposite possibility is that polio and flu viruses are more like
one another because of common ancestry and because of adaptations to the human

Needfully viruses have to have some genes that talk to the host genomes and
hence are similar to their host cells.  But that similarity could be due to
sharing a common origin or it could be due to adaptation.

The question to me is, are there enough genetic characters in viruses so that
one can reject a single or a multiple origin? build a cladogram(s)?

Don McAllister

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