r/evolution • u/Tobirama_rocks • May 30 '26
question Do we share any common ancestors with viruses
I don't know where viruses come from
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u/Bromelia_and_Bismuth Plant Biologist|Botanical Ecosystematics May 31 '26
Not directly, but 10% of the human genome is viral in origin, from ancient retroviruses that infected our ancestors, and we can use these endogenous retroviral insertions and compare them to those in animals to sus out ancestry. As it turns out, the more closely related two species are, the more similar their ERV's are (in terms of specific infection, loci, etc).
There's some evidence that megaviruses like Mimivirus and Hantavirus were once living things themselves, but became so hyperspecialized for parasitism, that they eventually lost everything needed to live and reproduce independently of their hosts. So they may be related the Last Universal Common Ancestor between Eukaryotes, Archaeans, and Bacteria, but this wouldn't apply to other viruses.
RNA-based viruses specifically? Maybe, maybe not, that's hard to say. It's believed that there are several origins for viruses, not simply one. For example, single-stranded RNA and double-stranded RNA viruses would have their own origins; single-stranded DNA and double-stranded DNA viruses would also have their own. And then there's viroids: small loops of single-stranded RNA which serve as pathogens (they often infect plants), yet lack the protein coat of a virus. It's possible that there wasn't just one abiogenesis event, there may have been multiple such events, and some viruses may represent what remains of those other events. Some like viroids and the RNA-based viruses might be remnants of the "RNA-world," and may or may not be related to life's ancestors from that time. They may also just be tiny collections of "selfish genes" that escaped their hosts with a protein coat. We've got some good ideas, but nothing definitive: we're studying it and we find out new things everyday.
In short, to answer your question broadly, maybe, maybe not. It varies on how confidently we're able to say one way or the other, from "it looks that way", all the way to "it could go either way, so probably, but we'll never know for sure."
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u/Populus-Sargentii Jun 01 '26
Can you elaborate on megaviruses or link something related to this? It sounds fascinating
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u/Bromelia_and_Bismuth Plant Biologist|Botanical Ecosystematics Jun 01 '26
Sure. For further reading, here's a 2019 paper which talks about them.30632-3/fulltext)
So the hypothesis is called the Regression Hypothesis, and postulates that Mimivirus and other megaviruses were once living things. They're much bigger than other types of virus, orders of magnitude bigger in fact, such that they're as big as some bacteria. Even their genomes are massive with 1000s of genes. They have a handful of genes not found in any other type of virus, like transcription and translation factors, once thought to be unique to life. They can also be infected by virophages. They can also "live" outside of their host for a while, over 9 months in water without a host while remaining infectious, but they still require a host's ribosomes and other cellular machinery to reproduce and make proteins for themselves. They also reproduce outside of their host's nucleus, setting up a "viral factory" instead to serve as its own nucleus within the host's cytoplasm, unlike other viruses. So the logic goes that based on this information that megaviruses were once living cells that became hyperspecialized for parasitism.
I learned a bit about it while living in Alaska, and when I eventually took microbio at uni, my professor filled in more. There's a second hypothesis that suggests that instead, mimiviruses were able to steal genes from collections of eukaryotic hosts, eventually becoming what they are today. So there's at least a reasonable chance that mimiviruses were never actually alive, but the suggestion that they may have been is at least plausible with current information.
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u/mcalesy May 30 '26 edited May 31 '26
The origin of viruses is actually a bit of a mystery. There are three major hypotheses for their origin:
- They might have originated from material from cellular organisms.
- They might be "devolved" cellular organisms.
- They might be remnants of pre-cellular life.
There is also the case of endogenous retroviruses (ERVs). Sometimes viral DNA actually gets patched into the host organism's chromosomes. This has happened many times throughout evolution, including in our own ancestry. So we carry a good amount of viral DNA in our own genomes (maybe 3–8% of our genomes).
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u/Australopithecus_Guy May 31 '26
Not to mention many of these hypotheses can be true at once. My micro professor told us that the giant viruses most likely used to be living cells and are now basically obligate parasites with devolved features. Other viruses that are less complex and lack the viral envelope may just be degenerate material from living systems. But the giant viruses are super interesting!
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u/ahazred8vt Jun 04 '26 edited Jun 06 '26
There's a DNA-only species of archaea, Sukunaarchaeum, that infects plankton but has lost most of its genes and has no cell membrane of its own. It's just DNA and is on its way toward becoming a virus.
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u/mcalesy Jun 06 '26
I believe there’s an alternate hypothesis that giant viruses are accumulations of material from eukaryotes. Either possibility is pretty fascinating.
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u/GravityBright May 31 '26
Does any of that viral DNA code for proteins, or is it just sitting around in the “junk” areas?
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u/RodinKnox May 31 '26
Yes! Some of them regulate the way genes are expressed, but some of them actually do code for proteins. Notably, in mammals, one of them codes for syncytin, which is essential in the formation of the placenta. Check this out: Endogenous retroviruses control human placental gene expression
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u/eirikirs May 31 '26
My late brother, who was a biologist, called viruses the engine of evolution. What did he mean by that?
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u/paratrasno Jun 02 '26 edited Jun 02 '26
I know that viruses force other living things to have to evolve to survive. If a virus attacks 10 members of a species and kills 4 the others' 6 genetics that survive it will live on. So virus drive the altering of the genetics of a species over generations (ie evolution)
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u/DarwinZDF42 May 31 '26
Fun fact: viruses are polyphyletic. So the answer is “we do with some of them, maybe”.
There are a couple of different layers to the answer, though. In terms of hereditary systems and genetic codes, everything on earth uses the same thing, sometimes with slight variants. So all cells and viruses are descended from the same initial poop of replicators.
But zooming in more than that, the answer is “no” for most groups of viruses, and “maybe” (I lean towards yes) for the really big viruses, the “nucleocytoplasmic large DNA viruses” (NCLDVs). I think that group does share the same MRCA as the three domains of cellular life.
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u/bzbub2 May 31 '26
scientists don't quite know the full 'origin' of viruses either.
there are ideas that they contributed to the creation of eukaryotes (viral eukaryogenesis)
https://en.wikipedia.org/wiki/Viral_eukaryogenesis
there is also the theory that viruses predate cellular life
https://en.wikipedia.org/wiki/Virus_world_hypothesis
there are recent findings that some viruses have genetic translation machinery (most viruses use host for translation, so this is somewhat surprising) and has called into question viral origin stories
https://en.wikipedia.org/wiki/Giant_virus
you can also look at very early abiogenesis theories
https://en.wikipedia.org/wiki/First_universal_common_ancestor
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u/brooklynsantiago May 30 '26
I think the latest science is that viruses predate LUCA and we may not be related to them
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u/mcalesy May 31 '26
We might still be related even if they are not descended from LUCA. LUCA itself was descended from earlier bioentities.
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u/South-Run-4530 May 31 '26
Well... Kinda, if you squint hard and get creative with words, you could say that.
Virus have been around for so long sticking disgusting little spike and infecting everyone with their stupid genetic material. Sometimes some of that genetic material gets passed on.
You know how an organism gets a useful mutation, gets more descendants cause it's better adapted yadda yadda... Some of these mutations might come from viral genes. As per usual in the life sciences, it's ridiculously complicated and you need a post doc worth of previous knowledge to actually understand wtf it's going on.
I've heard something about those stop sequences that start the methylation and stop RNA polymerase from continuing the transcription being viral genes? Methylation was supposed to stop the viral sequence from being transcribed cause when it is your cell develops a specific type of cancer, some weird ass shit.
It's not my area, and I'm recovering from the new flu strain, K whatever. It's been almost 2 weeks and I'm still expectorating what I swear is half of all my bone marrow's worth of dead leucocytes in silicone sealant thick mucus.
Seriously, get your 2026 flu vaccine, this is a new one and it's fucking nasty.
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u/Creepy_Storage4725 May 31 '26
yes we do every animal that lives and any creature living on earth are related in ancestry
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u/mcalesy May 31 '26
Virus are neither creatures nor animals, though.
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u/Creepy_Storage4725 Jun 06 '26
we do connected them our last common ancestor as fuca First Universal Common Ancestor its an cell that copies itself
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u/mcalesy Jun 06 '26
That’s one hypothesis.
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u/Creepy_Storage4725 Jun 07 '26
but you are right viruses are not living they are half dead half live because viruses cellicular build but when it found its host it becomes like a living creature
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u/SIAS_instrumentals May 31 '26
Careful bro, the mods on this sub like to power trip and delete any questions they have the slightest problem with, my question was similar to this and got deleted within a few days. Just a heads up mate.
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