Viruses as Evolutionary Forces

Introduction by the Blog Author

Quanta magazine from the Simons Foundation has a hypnotic article from the July 10, 2014 issue by Carrie Arnold.  It starts with a picture of a pithovirus, “the largest virus ever discovered — larger even than some bacteria. Many of its 500 genes are unrelated to any other genes on this planet.”

That caught my attention right there: a huge virus exists with a lot of genes, and many of those genes are not seen anywhere else on earth.  That’s inherently fascinating for a scientific mind.  Here’s more of what the article says:

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If giant viruses are as old as Caetano-Anolles’ calculated, the implications are staggering. It means that a giant virus or one of its ancestors existed before other types of life and may have played a major role in shaping life as we know it. This could mean that viruses are one of the dominant evolutionary forces on this planet and that each organism has a deep, viral past.

http://www.simonsfoundation.org/quanta/20140710-hints-of-lifes-start-found-in-a-giant-virus/

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[And think about this disagreement between two microbiologists included in the article above:]

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“Whenever you mix a bunch of small RNA molecules together, you get a bunch of parasitic sequences that aren’t good at anything except making copies of themselves faster than anything else,” Szostak said. For these sequences to become similar to modern viruses, they need to parasitize a living cell, not just another strand of RNA.

Dolja disagrees, saying that cells could not have evolved without viruses. “In order to move from RNA to DNA, you need an enzyme called reverse transcriptase,” Dolja said. “It’s only found in viruses like HIV, not in cells. So how could cells begin to use DNA without the help of a virus?”

[These two points of view are followed by a third theory:]

Abergel and Claverie, however, believe that viruses emerged from cells. While Forterre and collaborators contend that the unique genes found in giant viruses are a sign that they evolved before modern cells, Abergel and Claverie have a different explanation: Giant viruses may have evolved from a line of cells that is now extinct. According to this theory, the ancestor of giant viruses lost its ability to replicate as an independent life form and was forced to rely on other cells to copy its DNA. Pieces of these ancient cells’ genes survive in modern mimivirus, pandoravirus, and pithovirus, which would explain the unique genes found in this group. “Life didn’t have one single ancestor,” Claverie said. “There were a lot of cell-like organisms that were all competing, and there was one winner, which formed the basis for life as we know it today.”

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Footnote by the Blog Author

I also like the comments at the bottom of this article – they are good examples of how real scientists actually correct and clarify each other, itself something that shrivels when scientific research is politicized.