"A monstrous discovery suggests that viruses, long regarded as lowly evolutionary latecomers, may have been the precursors of all life on Earth...
Last July Forterre held a weeklong conference in Les Treilles, France, where two dozen of the world's leading microbiologists, cell biologists, and evolutionary biologists met to discuss "The Origin of the Nucleus." The nucleus, the command-and-control center of the eukaryotic cell, is ultimately what distinguishes a human from a bacterium. For eons prior to the emergence of the nucleated cell, life on Earth was essentially slime: vast, directionless mats of single-celled bacteria and archaea.
With no nucleus to further modify and craft gene expression and protein translation, life thrived but literally could not get hold of itself, could not assume new shapes or diversify. How the first nucleus came to be is a question that has intrigued scientists ever since Scottish botanist Robert Brown first detected a cell nucleus while peering at orchids under a microscope one day in 1824.
The discovery of Mimivirus lends weight to one of the more compelling theories discussed at Les Treilles. Back when the three domains of life were emerging, a large DNA virus very much like Mimi may have made its way inside a bacterium or an archaean and, rather than killing it, harmlessly persisted there. The eukaryotic cell nucleus and large, complex DNA viruses like Mimi share a compelling number of biological traits. They both replicate in the cell cytoplasm, and on doing so, each uses the same machinery within the cytoplasm to form a new membrane around itself. They both have certain enzymes for capping messenger RNA, and they both have linear chromosomes rather than the circular ones typically found in a bacterium.
"If this is true," Forterre has said of the viral-nucleus hypothesis, "then we are all basically descended from viruses..."
Information, whether biological or industrial, is passed along by replication. Create a new word-processing file and copy it: that's replication. But any replication process is susceptible to errors, which in turn can generate novelty. And novelty, especially in harsh, shifting conditions like those that prevailed on the newly formed Earth, is often an advantage: Some new life-forms will adapt better to the environment. To the utter abhorrence of the proponents of intelligent design, there is a certain randomness to evolution.
Some viruses, like Ebola or the new avian influenza, are basically runaway replicators, effectively burning their own life bridges in the process. But the majority, as Villarreal puts it, strive "to persist, not make a lot." Those that do persist eventually become both stable within, and staples of, evolution. The overwhelming majority of viruses are not harmful to their hosts. Each of us is infected with a huge array of viruses. The human genome, considered as a mass, contains more retrovirus sequences than actual genes.
"They're not doing anything," says Villarreal. "They're just persisting. And they were around long before humans evolved. The better part of the human genome is composed of viral DNA. That's true of nearly all eukaryotes, and the more complicated the organisms, the more of those sequences you have. We aren't sure exactly what they all do, but they are part of our genetic identity, this stuff we dismiss as junk. 'Junk' and 'parasite' are both words that will get you into a fight if you use them improperly. And yet they are where all life's creativity lies—its very origins.""
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