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jellyfixh t1_izaegsh wrote

Viruses have likely existed about as long as unicellular life, which is a very long time. And unicellular organisms have their own defenses against viruses, so once multicellular life developed the foundation of an immune system was already in place.

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bruceleroy99 OP t1_izapkus wrote

oh, ha, wasn't expecting that! I assumed viruses wouldn't be a thing until it was more "valuable", as it were, to attack another life - seems almost counterintuitive that it basically started off as a single cell attacking another single cell (this coming from someone that did very poorly in bio class XD). I would've thought it would be less efficient to attack another cell instead of just growing oneself.

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BetterLivingThru t1_izauhtd wrote

Viruses actually are not other cells, they're far, far smaller and simpler then cells, essentially just some RNA or DNA and enough protein to get into the cell and get to work, so it is very worth it for them to infect even tiny single celled organisms, since they are thousands of times larger than viruses, and viruses simply cannot reproduce on their own, unlike bacteria. There are, however, also bacteria that do infect and parasitize other bacteria, growing inside them and using their energy to grow and reproduce, like bdellovibrio bacteriovorus. There are also predatory single celled organisms, that eat other single celled organisms. Single celled organisms come in all kinds of sizes, and fill all sorts of niches in their ecology. Just as a leech cannot take energy and reproduce by photosynthesizing or by eating grass and has to be a parasite, so to do most of these organisms have no choice but to fill the roles they have adapted to fill.

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bruceleroy99 OP t1_izb8uig wrote

ooooh got it, that makes a lot more sense! extremely informative, too, thanks! I assume it isn't known at what point viruses / bacteria developed alongside everything? e.g. if single-celled organisms are 1000s x bigger than viruses, how big were things when viruses first started forming?

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clocks212 t1_izbtz5k wrote

It’s unknown whether cellular life came before viruses or if cellular life evolved from viruses.

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mcr1974 t1_izc29sd wrote

but what would have viruses attacked?

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the_quark t1_izc59cy wrote

They might have started simply as self-replicating sets of chemicals in the early ocean. At this point though we've only been able to speculate about their (and life's) ultimate direct origin.

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Octavus t1_izd243f wrote

There are also viroids which are even simpler than viruses. They are simply a circular strand of RNA, that is it. However they are still able to infect plants, use their cellular machinery to create more copies, and spread.

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astral_melum t1_izbcbgo wrote

Adaptive immunity, where an organism uses a host of specialized blood cells to defend against pathogens is (as far as we've been able to figure out) an evolutionary phenomenon of vertebrate animals. Multicellular animals also have innate immunity that likely evolved from unicellular defenses against infection by viruses and against predation. Some of the adaptive immunity blood cells (macrophages) look and act like single-celled amoebae in how they chase after and engulf their food. If you're not familiar with Kurzgesagt - In A Nutshell, they have a wonderful series of videos on this (and many other) science topics. I assign these videos to my entry-level college biology students to help them understand immunity.

edited for formatting

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scarabic t1_izd8pr8 wrote

The same answer goes all the way down really. There’s not a single chemical process or pathway anywhere in your entire metabolism that wasn’t invented in bacteria before multicellular life came about. Even photosynthesis originated in bacteria, long before there were plants.

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iayork t1_izdz6kl wrote

"Immune system" covers a lot of ground. The "immune system" that humans and other vertebrates have is a mishmash of evolutionary inventions going back well over half a billion years, that have been patched together with duct tape and bubblegum to form the rickety, clumsy and complicated apparatus that we know and love today.

Broadly speaking, the "immune system" gets divided into "innate" and "adaptive" branches. The "adaptive" part is what most people probably think of as "immunity:; it involved antibodies (B cells) and T cells. This arose in the ancestors of sharks, something like 400 million years ago.

Sharks and agnathans (jawless vertebrates, today represented by lampreys and hagfish) had a common ancestor maybe 550 million years ago, which did not have T and B cells as we know them, because lampreys and hagfish do not have T and B cells. (They do have their own analogies of antibodies, but they are a separate invention with very little in common with our antibodies.)

Although there have been some relatively minor changes in the vertebrate lineage, fundamentally we (and other mammals, fish, birds, reptiles) have the same immune system as sharks did.

The innate immune system is much older. We share recognizable components of innate immunity with insects. These include various pathways that recognize broad categories of pathogens, such as bacterial cell wall components. In vertebrates the innate immune system offers a large amount of rapid protection and also recruits adaptive immunity, which provides an initially slower but much longer-lasting protection.

Non-vertebrates don't have immune memory (you can't really vaccinate a bee, for example, though I know there are things that are rather sloppily called "vaccines") because "immune memory" is what the adaptive immune system does. Generalizing wildly, many invertebrates tend to be short-lived compared to vertebrates, which might make them less dependent on immune memory.

But of course there are very long-lived invertebrates too. In some cases invertebrates make much more extensive use of these innate immune components than vertebrates do. For example

>Detailed annotation of the Pacific oyster (Crassostrea gigas) genome, a protostome invertebrate, reveals large-scale duplication and divergence of multigene families encoding molecules that effect innate immunity.

--Massive expansion and functional divergence of innate immune genes in a protostome

Once you get much older than the vertebrate/insect split, immune molecules are harder to clearly identify. In bacteria, there are paths that protect against virus infection, but they are very different from the innate and adaptive immune molecules we see in eukaryotes. These include things like CRISPR and so on.

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Sharlinator t1_izbhltg wrote

Most living things don't have an immune system even today, because almost all living things are single-celled microbes. Of course, all living things have evolved in a constant arms race against parasites, so have all sorts of adaptations against getting infected, and infectious organisms of course are adapting all the time to overcome those defenses. But only complex multicellular organisms have "immune systems" with specialized cells and epigenetic memory and so on.

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DrBabbage t1_izcm3hi wrote

Some older species Like the horseshoe crab are still alive. The blood coagulates and for this, they are mercilesly hunted down and milked or drained completely. The blood is also made with copper as a base material. Fascinating creatures.

EDIT: Okay I thought I made things clear and easy enough to understand. Horseshoe crabs have very sensitive blood that clots up (coagulates) when it comes in contact with bacteria. Their blood is based on copper (Hemocyanin), unlike ours which is based on Hemoglobin or iron. Having the blood based on copper and clogging it up makes the blood very anti bacterial and is one of the earliest types of an immune system we know predating dinosaurs by a long shot. They are mercilessly hunted down to test vaccines since their blood clogs up in presence of bacteria but they are also eaten or used as fish bait.

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nimuehehe t1_izcmlu4 wrote

What does blood coagulating do?

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GeneralWorldliness38 t1_izcozoh wrote

coagulation of the blood, simply means when the blood solidifies and it gets clogged up. For instance in the medical field, when your doctor diagnoses you with blood coagulation, it refers to blood clot.

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