Submitted by Darth_Fatass t3_10ipbf3 in askscience
I've seen it multiple times that viruses have existed on earth for billions of years, but also that they don't appear in fossils. How do we know viruses are 3-4 billion years old? I've tried googling it but the answer seems hard to find
I use this video on PBS's YouTube that describes what we know so far, to my knowledge. It is a 4 year old video but I believe it still holds true. He also says that virus' have no fossil record because they're too small and fragile, so it's just because they can't survive that process. They're about as old as life itself, and in that is the question of how did life begin, where did we come from. I'd love to know more myself. Viruses are essentially part of the whole life / death balance if you look at it from a less scientific perspective, and their ability to mutate and infect / spread to survive is what allows us to keep questioning them the way we do.
first of all they're the most simple (and yet the most effective) life form, and therefore it's only logical they can represent one of the first steps in the evolution grand scheme (some scientists believe they evolved from a different branch of cells that sort of regressed tho): specifically the RNA ones are the oldest, since oxygen lacked in the old-earth atmosphere and that favoured RNA over DNA. Still, they cannot be older than cells themselves, since they need to use them to "reproduce". Very often some viral genetical mark can be traced way back in old DNA as well, and that can give you some sort if indication of the pathways the virus took to get the genetical configuration it has today, but apart from that it's really hard to put a pin in time.
Sorry for my english, it's not my first language
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English is my first language and you’ve explained it better than I could
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While it does not directly answer your question, if you're curious about learning more about viruses I recommend reading Carl Zimmer's A Planet of Viruses
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I only speak English and I don't know anything about this, but if I did, I couldn't have explained it better myself.
Nice explanation! I would add that the status of a virus being "alive" is a topic of heated debate, however.
One method:
(1) We can measure genetic drift rate of DNA.
(2) We can find partial or whole retro viruses encoded in DNA of animals such as humans because they insert themselves during replication.
(3) We can compare the viruses of today to the encoding of the virus in the DNA, and we know the age of the DNA due to the drift rate in (1). We can also therefore determine the age of the virus at time of insertion.
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Another method:
(1) Measure the mutation rate of similar viruses.
(2) Find old instances of the viruses from known prior historic periods.
(3) Compare the RNA patterns to find the mutations.
(4) Calculate the approximate age based on the mutations.
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Many other methods exist, and generally they line up. Reading:
"Yet, over recent decades it has become apparent that viruses occasionally leave a historical record in their host's genomes in the form of endogenous viral elements (EVEs)"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5962544/
LTR sequence divergence rates:
May I recommend this eye opening video
Viruses are directly involved in our evolution. As in, you have virus dna in your dna. This is how we can tell species apart and stuff like that and see when they branched off (rough paraphrasing) viruses have been merging with our dna for a long time and scientists can use this information to map out the tree of life.
Do viruses have DNA? Aren't they in between death and life?
Dude. At molecular level there is no life and death. It's just a machine
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Well, the question still remains and actually is, if they do not possess the actual machinery for them to replicate, are they actually a complete machine(alive)?
It makes no sense to equate a complete machine to being alive. Also, they do have DNA but not the machinery to replicate, which is why they have to take over cells as replication factories.
Yes they (mostly) do , this is what they insert into cells to get them to build multiple copies of themselves...
There are exceptions such as (from my memory, it's been a while since I studied) HIV which is a retrovirus, it uses stashes it's instructions as RNA.
The best way I've heard it described is, they are dead when outside a cell, alive when inside.
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At a certain point maybe it's not so useful to think of something as alive or not.
They do have DNA / genetic material. That means, whatever you want it to mean as far as if theyre living?
There are tons of cellular obligate parasites that render the discussion moot
that's how I see it too. On a molecular level, there are no "alive" tags so where's the line? With things like viruses and prion proteins, it's difficult to argue there really is a reasonable line.
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Yes viruses have DNA, and a protein body to aid in moving around and injecting into a target cell that's it. That's why they're not really quite an alive entity Because there are no self sustaining cellular organs that bacteria and etc have
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Some do, some don't. There's a pretty recent well-known virus that doesn't have DNA. Something with a corona in the name. The corresponding disease is COVID-19.
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Scientists use a variety of analytical methods to study the evolution of viruses and to determine their age. These include sequencing the genetic material of the virus, analyzing the virus's structure, and studying the virus's evolutionary relationship with other known viruses. By studying these factors, scientists can piece together an estimate of the age of the virus. Additionally, researchers have developed mathematical models to estimate the age of a virus based on its rate of genetic change.
What are mathematical models to estimate the age of a virus?
Depending on the type of virus, there are various mathematical models that can be used to estimate the age of a virus. For example, for RNA viruses, the substitution rate can be used to estimate the age. For DNA viruses, the substitution rate can also be used, but there are other methods, such as the coalescent model, which can also provide an estimate. In addition, the molecular clock hypothesis can be used to estimate the amount of time that has passed since the virus diverged from a common ancestor. Ultimately, the best model to use depends on the type of virus, but there are a variety of mathematical models that can be used to estimate its age.
I try to put it into words like this:
A virus can be understood to undergo different developmental stages. Much like an insekt goes from egg to larvar to adult, a virus goes from virus particle, floating alone and, debatably, dead in their environment, to integrating itself into the host. It quite litteraly overlapes with their victim, the cell becomes, to an extend, two individuals rolled into one.
Well, I understood dna to mean genetic basis in the context of this discussion, but yes. There are in fact RNA and DNA Viruses, which can further be divided in coding and non-coding strand (+ and -) based "liveforms".
There are also Prions, proteins that fold others with the same base aminoacid-chain into the same 3D struckture, in a kind of replication.
Viroids are naked, or non protein or membrane, associated chains of RNA, able to infect plants and responsible for some interesting patterns on some flowers.
To complete the picture there are also gigant virus out there, with their own molecular maschinery responsible for about halve of our atmospheric O2.
These are complex little suckers. And I both love them for it and hate them with a passion.
[deleted] t1_j5gkqwa wrote
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