Data published by the International Human Genome Sequencing Consortium indicate that somewhere between 113 and 223 genes present in bacteria and in the human genome are absent in well-studied organisms—such as the yeast Saccharomyces cerevisiae, the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans—that lie in between those two evolutionary extremes. Some researchers thought that these organisms, which arose after bacteria but before vertebrates, simply lost the genes in question at some point in their evolutionary history. Others suggested that these genes had been transferred directly to the human lineage by invading bacteria.
My colleague Victor DeFilippis of the Vaccine and Gene Therapy Institute of the Oregon Health and Science University and I suggested a third alternative: viruses may originate genes, then colonize two different lineages—for example, bacteria and vertebrates. A gene apparently bestowed on humanity by bacteria may have been given to both by a virus.
In fact, along with other researchers, Philip Bell of Macquarie University in Sydney, Australia, and I contend that the cell nucleus itself is of viral origin. The advent of the nucleus— which differentiates eukaryotes (organisms whose cells contain a true nucleus), including humans, from prokaryotes, such as bacteria—cannot be satisfactorily explained solely by the gradual adaptation of prokaryotic cells until they became eukaryotic. Rather the nucleus may have evolved from a persisting large DNA virus that made a permanent home within prokaryotes. Some support for this idea comes from sequence data showing that the gene for a DNA polymerase (a DNAcopying enzyme) in the virus called T4, which infects bacteria, is closely related to other DNA polymerase genes in both eukaryotes and the viruses that infect them. Patrick Forterre of the University of Paris-Sud has also analyzed enzymes responsible for DNA replication and has concluded that the genes for such enzymes in eukaryotes probably have a viral origin.
From single-celled organisms to human populations, viruses affect all life on earth, often determining what will survive. But viruses themselves also evolve. New viruses, such as the AIDS-causing HIV-1, may be the only biological entities that researchers can actually witness come into being, providing a real-time example of evolution in action.
Viruses matter to life. They are the constantly changing boundary between the worlds of biology and biochemistry. As we continue to unravel the genomes of more and more organisms, the contributions from this dynamic and ancient gene pool should become apparent. Nobel laureate Salvador Luria mused about the viral infl uence on evolution in 1959. “May we not feel,” he wrote, “that in the virus, in their merging with the cellular genome and reemerging from them, we observe the units and process which, in the course of evolution, have created the successful genetic patterns that underlie all living cells?” Regardless of whether or not we consider viruses to be alive, it is time to acknowledge and study them in their natural context—within the web of life.
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12 Comments
Add CommentI think that whether or not viruses are "alive" (whateve THAT means) is immaterial to whether they impact evolution. There are plenty of non-living things that impact evolution (like plate tectonics and other non-biological environmental factors). Evolution, by it's very nature, does not exist in a vacuum. Even if viruses are "non-living" the fact that they affect "living" things (particularly the fact that tey do this by phyiscally invading and biochemically changing "living" cella) means their impact on evolution cannot be ignored. Their impact on evolution may be different from, say, bacteria's effect, but that doesn't mean the effect doesn't exist.
Reply | Report Abuse | Link to thisJust another example of how narrow-minded people can be when the become highly specialized. Specialists are essential, but they need generalists to keep them grounded in something akin to reality.
My, my, it sounds to me that viruses may be God's little screwdriver used to tweak his creation. Just another mild blurring of the spirit/science boundary.
Reply | Report Abuse | Link to thisThe issue of whether or not a virus is alive is simple to resolve, in my opinion. So long as we recognize that life is just functioning molecular machinery, mesomachinery, then grasping the place of the virus becomes trivial.
Reply | Report Abuse | Link to thisA virus is a static bit of mesomachinery, of molecular machinery, on its own, which only functions when inserted into an active machine, such as a cell.
There is no need to specify 'life' as some special or magical thing. Life is molecular machines in action, death is cessation of that function without hope of restart, and a virus is just a snippet of organic computer code that requires a running program in order to be acted upon. The code is mechanical, biology as a molecular Babbage engine, virus as... a virus, a computer virus, in physical, molecular machine form. Nothing more, nothing less.
And as for you and I? We are electrochemical programs running on walking, talking mesomachine systems. Nothing more, and nothing less.
'Life' is a process, the program running, not a thing.
If life is defined by the ability to respire then a virus is not living!
Reply | Report Abuse | Link to thisMissing from this article is the idea that the mitochondria in eucaryotic cells may well be viral in origin. The DNA is unique, passed down by the mother only, and could not have evolved by any accepted evolutionary standards.
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Reply | Report Abuse | Link to thisPer the virus question, here's my 2 cents worth: The virus has an existence dependent on DNA/RNA sequences (whatever that may amount to), plus it can be killed off... Genetics, plus it can die, means to me that it must be alive..
Reply | Report Abuse | Link to thisViruses are both, dead AND alive. Outside a living cell they are nothing but a large complex of organic chemicals. Inside the cell they assume some properties of life. I believe it's impossible to truly create life from inert matter, without using another life form to assist in the process. Or at least we are a very long way from it.
Reply | Report Abuse | Link to thisSince it is now fairly easy to create certain viruses from scratch, as done by Eckard Wimmer of Stony Brook University, I think it's not really life that's being created, but rather at best "re-created" from known information. This life can be "molded" within certain parameters to be put to good use, for instance in the making of new vaccines, as the groups around Eckard Wimmer and Steffen Mueller subsequently showed (some explanation found here: http://ms.cc.sunysb.edu/~smueller/index.html )
The closest thing to creating some type of new life form is the group around Craig Venter. They use a completely synthetic bacterial genome, and try to transplant it into an empty bacterium, which had its genome completely taken out. However, as I said this process depends on an empty surrogate bacterium, which contains all the "stuff of life" in form of thousands of different proteins, EXCEPT the information (i.e genome) to replicate itself. So, even if they succeed in doing that, it may new life form, and after "booting" it from the synthetic genome, it will assume the properties encoded by the new genome, but it first needed that "empty" bacterial shell, and THAT perhaps can never be made from scratch, because it is way too complex.
I like the idea of looking at viruses as seeds. Viruses are seeds that do not give rise to an organism, but only produce more seeds. Sometimes these seeds implant themselves into the human genome and grow into part of the human organism.
Reply | Report Abuse | Link to this1+1=2; 1x1=1; abc; point,line,plane; triangle, square, circle. what is the minimum definition of life?
Reply | Report Abuse | Link to thisvirus does NOT qualify. there is NO gray area. unless you want to change the definition soley to include the lowly virus.
go back to the basics. biology 101.
maybe a more appropriate term: sub-life?
Well, anything that isn't dead...is alive...yes?
Reply | Report Abuse | Link to thisObligate parasites that depend on their host as replication machines - I hardly call that alive, since they are not independent, not even at a cellular level. This is no different than computer viruses that depend on executable programs to replicate itself: Not life, but replication machines only. Technically that's what all life does - EXCEPT - living things are of their own organism even if it's an individual cell. (Even though all life feeds off of life but that's a moot point - living things are their own entity).
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