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Ed Rybicki, a virologist at the University of Cape Town in South Africa, answers:
Tracing the origins of viruses is difficult because they don't leave fossils and because of the tricks they use to make copies of themselves within the cells they've invaded. Some viruses even have the ability to stitch their own genes into those of the cells they infect, which means studying their ancestry requires untangling it from the history of their hosts and other organisms. What makes the process even more complicated is that viruses don't just infect humans; they can infect basically any organism—from bacteria to horses; seaweed to people.
Still, scientists have been able to piece together some viral histories, based on the fact that the genes of many viruses—such as those that cause herpes and mono—seem to share some properties with cells' own genes. This could suggest that they started as big bits of cellular DNA and then became independent—or that these viruses came along very early in evolution, and some of their DNA stuck around in cells' genomes. The fact that some viruses that infect humans share structural features with viruses that infect bacteria could mean that all of these viruses have a common origin, dating back several billion years. This highlights another problem with tracing virus origins: most modern viruses seem to be a patchwork of bits that come from different sources—a sort of "mix and match" approach to building an organism.
The fact that viruses like the deadly Ebola and Marburg viruses, as well as the distantly related viruses that cause measles and rabies, are only found in a limited number of species suggests that those viruses are relatively new—after all, those organisms came along somewhat recently in evolutionary time. Many of these "new" viruses likely originated in insects many million years ago and at some point in evolution developed the ability to infect other species—probably as insects interacted with or fed from them.
HIV, which is thought to have first emerged in humans in the 1930s, is another kind of virus, known as a retrovirus. These simple viruses are akin to elements found in normal cells that have the ability to copy and insert themselves throughout the genome. There are a number of viruses that have a similar way of copying themselves—a process that reverses the normal flow of information in cells, which is where the term "retro" comes from—and their central machinery for replication may be a bridge from the original life-forms on this planet to what we know as life today. In fact, we carry among our genes many "fossilized" retroviruses—left over from the infection of distant ancestors—which can help us trace our evolution as a species.
Then there are the viruses whose genomes are so large that scientists can't quite figure out what part of the cell they would have come from. Take, for instance, the largest-ever virus so far discovered, mimivirus: its genome is some 50 times larger than that of HIV and is larger than that of some bacteria. Some of the largest known viruses infect simple organisms such as amoebas and simple marine algae. This indicates that they may have an ancient origin, possibly as parasitic life-forms that then adapted to the "virus lifestyle." In fact, viruses may be responsible for significant episodes of evolutionary change, especially in more complex types of organisms.
At the end of the day, however, despite all of their common features and unique abilities to copy and spread their genomes, the origins of most viruses may remain forever obscure.
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31 Comments
Add CommentGreat article!
Reply | Report Abuse | Link to thisI've wondered myself how the virus came to be. It occurred to me that maybe what we see as a virus today is what's left of life's earliest attempts at sexual reproduction. But I guess we'll never know.
I feel strongly virus is one agent of evolution of life on earth. Are they also the agent of life?
Reply | Report Abuse | Link to thisHow about a bit wilder idea, viruses evolved before celular life.
Reply | Report Abuse | Link to thisLike snipsets of biocode, some wrong combinations of carbon code who never turned out to become realy alive. Altough in a primordial soup they might have worked together. Later some co-operated and formed unities protected by cell wands.
Just some deeper life origin phylosopics.
Viruses started at the beginning. In the soup of aminos and bits delivered via comets, the virus is likely the original pre-life.
Reply | Report Abuse | Link to thisFrom an evolution perspective, perhaps the first virus evolved as a product of bacteria, a sexual DNA carrier, allowing bacteria to mix DNA without an actual physical connection. This would be a bacteria's phone sex equivalent.
Reply | Report Abuse | Link to thisWhen I struck by viruses,how can I know it,dose it has any impact to me?
Reply | Report Abuse | Link to thisGreat article about the evolution of viruses...It is an ambiguous subject as nothing is definite, but many pieces of a puzzle that still needs to be put together! Awesome insight...I loved genetics in university!!! Thank you for sharing this...
Reply | Report Abuse | Link to thisKimberly Edwards :)
http://BlogNButter.com/health
Why are most scientist so eager to not point their finger at the most usual placeses for the origin of viruses--They are an Alien thing--They were brought here millions of years ago--by the most obivious ==Aliens =Viruses are not of this earth--Most likely from mars-& the moon==Because they are pretty close to us!And they are for the most part Dead Bodies in space!!Viruses& bacteria are the means that things that are dead--waste away --At one time The earth was all Vegitation-& Beasts--They died of because of Bacteria& Viruses!!
Reply | Report Abuse | Link to thisthose of us who find long therm interest in the subject wer disappointed. i expected a somewhat more conclusive artival from sciam. well written but poor in information
Reply | Report Abuse | Link to thisI belive it likely that viruses predate biotic life as we know it. Amino acids form readily in the type of atmosphere that Earth is believed to have had at that time and would have accumulated in the water. Reactions of these amino acids on clay substrates could have produced RNA type strands that could have catalyzed simple proteins. These in turn eventually produced a protein sheath for the virus. As the virus RNA strands developed in complexity eventually they produced cell capable of internal metabolizm and simple asexual reproduction.
Reply | Report Abuse | Link to thisHe never comments the origin of viruses Only how time ago they could appear
Reply | Report Abuse | Link to thisI appreciate the comments - the ones that make sense, anway B-) - and also agree that I did not commit to exactly where viruses came from.
Reply | Report Abuse | Link to thisThe fact is, the are a number of origins; they share as a group only their lifestyle as obligate intracellular parasites, which in my mind is a prime example of convergent evolution.
See http://rybicki.wordpress.com/2008/03/19/from-what-did-viruses-evolve-or-how-did-they-initially-arise/ for a more complete version of this article.
If viruses are competent in natural genome editing as it occurs obviously in endogenous retroviral agents like mobile genetic elements it seems likely that they represent the basic elements of pre-cellular life
Reply | Report Abuse | Link to thisGWitzany: if viruses were the original genetic elelments -or at least, ones like retroviruses were - there wouldn't have been any other genomes to "naturally edit"...B-)
Reply | Report Abuse | Link to thisIt is quite possible that SOME elements of SOME viruses could have originated in the very dawn of the evolution of our planet's lifeforms - but the ones we know today are very far removed from those original forms, and have picked up - by acquisition of modules by "horizontal gene transfer" - other genetics elements, which muddies the picture of where they came from considerably.
Where DID viruses come from is a very simple question to answer... along with everything else, they evolved from the PREbiotic earth. There is absolutely no mystery about it, in a Universe and ontological reality "naturalized" and demystified by scientific endeavor.
Reply | Report Abuse | Link to thisWhat is interesting is whether the peering back by humanity to seek the origins not "of the specie" but of life itself will define exactly what role the most elegant and simplist of life forms played, the RNA virus.
Abiogenesis has long been the proverbial last card to fall in the House O' Cards otherwise known as creationism (aka intelligent design or irreducible complexity}. The "RNA world" hypothesis, along with other basic "replicant" molecular possibilities seems to carry persuasive force. The fact that a "viral mechanism" exists and its facile ability to modify genetic information seems to argue for it being a fundamental mechanism for the emergence of biologic life.
Deus sive Natura... it matters not.
I find this a very interesting topic. Viruses inhabit the realm between life and the inanimate, something quite foreign to our traditional world-view.
Reply | Report Abuse | Link to thisWow, does everybody on here believe viruses are prebiotic survivors? I happen to be reading this book right now by Christian de Duve, called [u]Vital Dust[/u] (I'm only nearing half-way through but I'd highly recommend it). Now it is a bit over 10 years old now, which I know is an eternity in the emerging biotechnological sciences, but the author seems to strongly suggest that viruses are actually streamlined, or genetically depleted, descendents of bacteria. He suggests that, in the Darwinian struggle, unnecessary phenotypic luggage is quickly abandoned, when for the sake of metabolic efficiency, etc. The idea is that eventually they lost so many (formerly) vital genes that they forever lost the ability to return to the autonomous world.
I wondered if the author or someone else could shed some light on whether or not this still a respected theory. Also, since viruses are obligatory parasites, how could they have possibly been around before "life?" And if they could survive without a host, then can we really even call them viruses in the sense we know? Are you all imagining a primeval soup-style superorganism where the mechanisms for replication were mixed and free-floating, as opposed to encased in membranes?
Using the term "viruses" as a homogenous term is fraught with pitfalls regarding both their nature and origins... as it is a very diverse group, both in a metabolic-biological sense... as well as evolutionary.
Reply | Report Abuse | Link to thisSimple, elegant SS RNA viruses with a few rapidly evolving genes cannot be directly compared to "large" Herpes or Pox virues comprised of DS DNA and hundreds of genes.
Besides the medical interest due to myriad viral disease and genomic applications for "viral vectors" for production of medically useful proteins ("gene therapy") or targeted oncology therapies... the larger question is how they have co-evovled (speaking of the DNA variety) with their hosts and what role the RNA and retro-viral replicants played during the emergence of "celllular life".
I recently read where viral gene alterations were fundamental in the evolution of mammalian placental function!
Similarly, we are dependent upon the resident enteric (gut) bacteria to avoid pathogenic infection and sepsis.
Anyway, it is very interesting to (atttempt) to follow viral research regarding the emergence of life, and it's profoundly complex, intimate and inter-dependent evolution among all species, particularly humans.
Cheers.
Thanks Spinoza (my fav philosopher, btw, I love the fact that he just worked diligently on his main life's thesis (The Ethics) while working as a lens maker (also a wonderful metaphor...:^O), and only after he died did his friends compile and publish it...what lack of selfishness, imho, anyway, sorry...).
Reply | Report Abuse | Link to thisYea actually I went back and looked at the author's link to the (very much better) original version of the article. It sounds like he was saying that some viruses are simply too simplistic to be diminished bacteria. That whole blog and the links within are great (the stuff on nanobacteria, or prions, was very interesting).
I thought I remember seeing that some of those very tiny SS RNA viruses strongly resemble mRNA. I'm certainly no expert on this stuff, but I'm assuming that, once in a host cell, the virus (m)RNA finds a host ribosome and is thereby translated into proteins that allow the virus's RNA to replicate? Or are all these viruses reverse transcription viruses that must transcribe their RNA into DNA (using the host cell's machinery?) and then from there the host's machinery helps the virus replicate? Would the former more support the prebiotic origin hypothesis (because DNA is nowhere involved)?
The root of my query is the fact that ribosomes must be incredibly complex molecules. Is there any way they could have developed in some fashion before the cellularization of life? I thought I remember reading in some life's origin theory, that the first RNA strands would have had to have been self-translating. Could this have been done through some catalyst already in the environment? Wouldn't any other way lead some version of the "chicken and the egg" problem (i.e.. how could something create the means of allowing itself to create)? Its not like I keep up on this stuff so my info may be way outdated or something.
One more thing, just as kind of a poll: Do you all feel strongly one way or the other about whether viruses are "alive?" Is the distinction between life and non-life just an archaic residue of the tens of thousands of years of human existence before the invention of 'extra sensory perception,' for poor choice of words, like microscopes, for example? Is the whole argument just a useless semantic diversion?
Eloheim:
Reply | Report Abuse | Link to thisYeah... Spinoza was a true iconoclast regarding the dogmatic thinking of the religious... as well as the first pantheist or panentheist. Einstein claimed he did not believe in god, other than "the god of Spinoza"... which is to say, Nature or the Cosmos of Sagan. Also, like myself, he was an utter determinist.
Anyway, it seems clear to me if PANspermia was not solely the big push for abiogenesis, the most likely candidate was RNA or some form that closely approximates it. It solves the replication+information+catalytic+regulatory functions necessary for precellular life, before more complex protein driven metabolism and specialized genetic-info storage via DS DNA and histones. Thus, this is no "chicken and egg" problem.
I used the term [b]RNA world[/b] earlier to clue others in to the real origins of this now viral transitional evolutionary form.
As for ribosomes... they are not that incredibly complex as I think you phased it.... and the business (catalytic) portion of the molecule is strictly rRNA... again, only a marginal, secondary role for proteins... which were clearly not required for life to emerge.
It is obvious that this early RNA-like molecule evolved to more efficiently perform specialized functions.... and DNA and proteins were selected as more efficient for the genetic and metabolic roles. rRNA is probably the evolutionary signature of the primitive abiogenic form.
RNA viruses most likely were the first "life forms" if we define life by the functions I listed above.
Cheers.
It is my opinion that viruses are simply DNA scraps, or remnants of DNA that were in the mix with the first life forms. They have "survived" the same way prehistoric plants and bacteria did, by combining with other chemical building blocks at their attempt to evolve.
Reply | Report Abuse | Link to thisAh, I see, Spin. And your point about the complexity of the ribosome (or some kind ancient approximation there of) is well taken. I once read a hypothesis that the very original RNA language could have lacked a bit of the rigid specificity enjoyed by the genetic code of today (although I do seem to recall something about the third letter of some codons not changing which amino acid is assembled, maybe?). Granting this prebiotic virus origins theory, I would assume that the viruses then adapted the presently seen version along with their host organisms.
Reply | Report Abuse | Link to thisGod, I hope I get to live to see the day we make a detailed exploration of some of those oh so intriguing moons of Jupiter and Saturn, or even really dig into Mars, for that matter. It's always going to be difficult to judge these kinds of life's origins theories when we have only one example to take from.
The nanozoa have yet to be formulated into a group for study, but viruses and other bits or rna and dna associated particles are along with associated enzymes and protein substrates form a proper set. As with microbes we will find that nanozoa are far more numerous and extensive than we can currently imagine. The activities of the nanozoa do not have to have a moralkty imposed on them. The outcomes of these actions and interactions will be creative and destructive and subject to the fractal nature of the probability spaces in which they occur. The transformational nature of most viruses is an indication of the underlying transformation of the nanazoa within the fractal spaces. The spinning twisting and weaving of the nanazoa is related to the vortex activity within infinite possibilityspace fractaly distributed. jehovajah
Reply | Report Abuse | Link to thiswell nanozoa have yet to be tested fr other natrual uses such as cures but viruses were made by accident by man-kind for wehave made many mistakes in life for whichwe use today.We use virusesfor cures sometimes wemust mixs them together so that we may find more cures for man-kind.
Reply | Report Abuse | Link to thisI can't help but wonder if these viruses were created around the time life was created. Viruses have been proven to play a MAJOR role in evolution. Are viruses solely responsible for evolution? Was Darwin wrong...?
Reply | Report Abuse | Link to thisI know that love is truth, and Darwin's theories were void of any of that.
Hello,
Reply | Report Abuse | Link to thisCheck-out this new theory about the origin of viruses. It explains the relation between viruses and sexual reproduction.
http://harmonic-resonance-with-julien-justal.blogspot.com/2009/11/lets-rename-hiv.html
The idea is that viruses have emerged and diversified from unicellular organisms at the same time as unicellular sexual organisms have emerged: viruses and sexual reproduction comes from a growing asymmetry in non unicellular reproduction. Some of the cells have specialized in becoming parasites of others which among which some continued specialization in sexual reproduction and creation of multicellular organism. Viruses are intrinsically liked to the evolution of species and continue to live in symbiosis with our organism. The very fact that genetic mutation occurs randomly create a differentiation of living organism which enabled at the same time the emergence of viruses and sexual reproduction. To oversimplify, it's like cells used to reproduced spontaneously and as they diversified some cells where able to reproduce with a cell that was more and more different leading to progressive creation of sexual reproduction while at the same time other where accelerating genetic mutation when parasiting the genome of other cells. The dynamics between diversified cells is at the very basis of understanding immunity, difference between living organism and mineral organisms and ultimately regulates life and death.
Enthusiastically yours,
Julien
I've been working on an astronomy book with many tangents for about twenty years. Tangents include astrobiology, origin of life, panspermia, microbes, viruses, and now the origin of viruses. Do some viruses have a common origin or common ancestor that pre-dates Earth? I think your interesting article says possibly. I just finished re-reading part of a book by science writer Marcia Bartusiak about interstellar molecules.
Reply | Report Abuse | Link to thisHunting for the "seeds of life" seems to me perhaps like looking for a needle in an exponential haystack, but it would only take one or two seeds to start a civilization if they landed in a fertile environment!
Altho I've just scratched the surface of this subject, it strikes
me that viruses are a very challenging genealogy project.
(You're the only Virologist I've heard of, as well as the only one whose name like mine ends in "cki".) - Tony Rozycki, arozycki@aol.com
Nice aloha shirt!
waterdog's answer is basically the same as mine except that i believe that viruses and cells developed alongside each other and interacted to produce a working reproducing virus
Reply | Report Abuse | Link to thisI agree with JakeDavidson. This is the most likely candidate. Proteins are kind of like legos, in that they fit together in certain ways. Obviously the combinations are nearly limitless, so I can imagine a sea of viruses with sligtly different attatchment mechanisms as a good vehicle for releasing DNA and increasing the small chance it might couple with another organism or simple cell and replicate something meaningful and survivable. So viruses could have been, and may still be, a "promiscuous" way for bacteria to replicate. Promiscuoty always provides more viable offspring.
Reply | Report Abuse | Link to thisViruses are one of the "Cross-Universe Gene's cariers creatures".
Reply | Report Abuse | Link to thisThe are therefore basically diffrent from on-earth-living creatures.
They are built and can survive for ages, in space, atmosphre or underground, on or between strars.
Earth is one of the places where they manipulated molcules to become a living sell (STARTING FROM BACTERIA TO ALL OTHER LIVING CREATURES ON EARTH ) in which the multiply and improve their genes.
ON OTHER STARS THEY DEVELOP OTHER CREATURES TO use for their needs including REPRODUCION.
D.Ouziel.
by definition life is a cell, the word cell means that is a prison and what is inside the cell, prisoners. viruses are not cells, therefore are not alive. it would be assuming alot to say they predated cells, we don't know the origin of cells some claim they do but those are just claims and nothing more. until we can prove and create cells which don't come from other cells i will remain sceptical of that issue.
Reply | Report Abuse | Link to thisviruses are not alive simply because they are not cells. we do not need to define the characteristics of life for this matter at all in my opinion. where they came from is whereever your imagination thinks they did. where did anything come from? it is more reasonable to suggest they did not predate life simply because they are obligate intracellular parasites. life created viruses like it creates other organic molecules, that is the property of being alive. being able to synthesise is the characteristic of life. maybe life stopped creating viruses at some stage, we will never know due to the vast numbers of viruses. you never know where a new virus was formed, it is not like you can trace it's genealogy. can we eliminate the possiblity that life is constantly creating new viral dna somehow out of cells? if not, then how can you say they are alive?
http://my.opera.com/jehovajah/blog/2012/03/11/nanozoa-and-nanozoe
Reply | Report Abuse | Link to thisSince i coined the term some developments in evolutionary concepts for the archaea have emerged which in my view link viruses and DNA development.
http://my.opera.com/jehovajah/blog/2012/02/19/venom-and-viruses