Viruses are Largely Unrelated to Life on Earth. Where Do They Come From?

It seems like the arguments made in the article would more readily support the idea that viruses are spontaneously forming on Earth than in space. If viruses are spontaneously forming on other planets or in interstellar space directly, then they should be forming on the Earth as well. I think the Earth is more likely for a number of reasons.<p>To start, viruses are generic material wrapped in proteins. The functionality of proteins depends on their shapes and the environment strongly affects the shape of a protein. Viruses that exist on Earth have proteins that are stable on Earth. A virus that comes from a different environment would be liable to fall apart on the Earth. RNA itself is pretty unstable by itself (hence why cells use DNA), but there are plenty of viruses that use it as their genetic material.<p>Infecting host cells is another matter. Viruses are generally pretty specific with their host cells. They enter host cells by binding to specific proteins on their surfaces. Once inside they take advantage of the specific cellular machinery present. For example, the polio virus has a single strand of RNA that codes for a single long polypeptide that is then sliced at specific point by host enzymes to produce the final viral proteins. Some viral proteins act to suppress the defenses of the cell and the immune system in general. An alien virus would be insanely lucky to be able to infect local life at all, let alone reproduce and spread. Unless life across the universe is incredibly similar.<p>Given these thoughts, it seems like it would be more likely for viruses to spontaneously form on Earth than another planet (or interstellar space). Viruses forming on Earth would have the advantage of starting with organic materials that already work with existing life. The Earth is generally protected from harsh radiation and extreme temperatures. The most important thing is that any forming viruses would have immediate (relative to crossing space) contact with host cells to infect and evolve.<p>The only reason it wouldn&#x27;t be happening on Earth is if the Earth is completely unsuitable for it. Even if both are happening, the vast distances and harsh nature of space should shift the equilibrium strongly towards native viruses. But if the Earth is unsuitable for it then how are viruses able to survive and reproduce on a planet that&#x27;s so unsuitable for them?

To me the real question is whether any particular virus lineage evolved independently, or started out as an organelle or other apparatus of a cell, and got loose.<p>I doubt we will ever know, about most viruses, because they evolve so fast. But it would be seriously cool to find a bacterium using them for communication or as an extra-cellular library.<p>We already know about plasmids, of course, and there are plasmid viruses that dispense with the protein wrapping. But do any bacteria communicate, or store information in the environment, via non-viral genes wrapped in a viral protein coat? Would we notice if they did?<p>We still would not know whether the bacteria co-opted a virus, or developed the mechanism by itself. Indeed, it could be that the original developer of, say, those mosquito-shaped phages was wiped out when they went rogue.

On the face of it that statement appears to be self-contradictory, given that viruses use RNA or DNA, like all life on Earth?

Every time evidence leans the author towards &quot;viruses might come from space&quot;, I find myself leaning the other way.<p>My general view is that cellular life and viruses mutualistically co-evolved from life-like junk at the very beginning. Cells provide the metabolisms necessary to fight entropy. Viruses promote genetic diversity while acting as a stress-test to ensure cells can survive their environments. This seems separate from the trichotomy offered: - Virus first - Reductive virus - Escaped genes<p>&quot;If viruses originate from the cells that they interact with, one would expect there to be significant genetic overlap between the host and the parasite&quot;<p>The generally small amount of genetic material in a virus is being used for <i>viral</i> reproduction. I assume most functions encoded in the genomes of cells are useless and expensive for a virus to replicate. Hence, they&#x27;ll drop out; we&#x27;ll be left with oddball viral genes for viruses to do virus things.<p>[clipped list of reasons] &quot;All of these facts together suggest that viruses are the raw material from which living creatures build their genetic material. They’re like bricks in a building, ...&quot; I think of viruses more as clipboards (like copy-paste in your OS). Great for moving info around, but wholly dependent on a cell metabolizing somewhere. Hardly building blocks.<p>&quot;If that’s the case, it’s possible that the absolute simplest viruses, ones who consist of genetic information encased in a capsid made from a single repeating subunit, could be abiotic products of the cosmos. If that’s the case, we would expect to still find viruses as you got further and further away from the surface of the Earth.&quot;<p>Considering the density of viruses in the ocean (mentioned by the author), it seems a simple gust of wind would be enough to cover the earth in viruses.<p>I believe extraterrestrial life is nearly certain and that viruses can survive in space. I also think viruses depend on host cells to reproduce. A virus would have to land in the primordial soup to be of any life-generating use. By that point there would be enough lifelike junk for the virus to be an unnecessary step in the recipe.

Some viruses have only 2 genes. One for a protease enzyme, one for their outer shell. 2 genes. Isn&#x27;t that incredible?

Where in the article does it say that &quot;Viruses are Largely Unrelated to Life on Earth&quot;?