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Comment by blacksmith_tb | Hacker News Reader

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

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Agreed, some of the reasoning for extraterrestrial origins of viruses could also be explained by terrestrial processes. For example, the fact that new viruses are being added as quickly as old ones degrade and disappear doesn't necessarily mean alien viruses, but could also be reservoirs of ancient viruses being released into the environment or rapid mutation of existing viruses. Viruses having an extraterrestrial origin implies either RNA is spontaneously self-generating in the universe in large quantities, or somehow getting carried over across interstellar space from an alien ecosystem, and there's not a lot of evidence for either case. But given that viruses can survive intact for long periods of time since they don't have to perform biological processes (and maybe even longer underground away from degrading UV light) and the vast diversity of life that has lived and gone extinct on this planet, I'd be more inclined to think we're getting infected by Mammoth diseases rather than Alien diseases.

This theory is less convincing when you consider that viruses don't seem to share any common genetic ancestry with organisms living today, but they could share genetic ancestry with extinct organisms that didn't leave leave any living descendants with genetic mutation adding even more obfuscation to their origins.

The last part of that is an interesting theory. Would you expect to see a lot of relatedness between different viruses if that were true?

I don't think you'd even have to look at extinct life. There's so much life that hasn't been categorized. You can basically take a soil sample from anywhere in the world and find new microorganisms in it. Archea are a great example of this. They're small, single celled organisms. They're best known as being extremeophiles, but exist basically everywhere. But the majority of them are difficult to culture and study. What's particularly interesting is that viruses that infect archea are known to be very different from other viruses.

So the crazy thing is that if you take a teaspoon of soil and sequence it for bacterial information, almost all of that information is similar to what's been found elsewhere. If you take that same teaspoon of soil and look for the viral genetic information in there, it's wholly unique. They seem completely unconnected to the rest of life, as far as nucleic acid signatures go.

To play devils advocate, cells use RNA and DNA so an alien virus that uses a different type of genetic material would likely be unable to reproduce in cells that use such a strikingly different biochemistry. Detecting such viruses would be incredibly difficult especially since our biotech is focused on DNA and RNA.

If you sequence a virus and it has no genes that are found in any living organism, then it's hard to say that they're related... since all our definitions of relatedness come down to sequence similarity.

We haven't found nucleic acids, as such, in extraterrestrial environments, but we also haven't been looking very hard. Nucelobases, but nothing that seems to encode information. However, most conventional explanations for the origin of life include spontaneous formation of genetic information, driven by environmental conditions. If genetic information alone can be spontaneously formed, why couldn't the simplest viruses be generated by the same principle?

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