Ancestors

Written by John Carlos Baez on 2025-01-15 at 18:11

Wow! Biologists seem to have discovered an entirely new kind of life form. They're called 'obelisks', and you probably have some in you.

They were discovered in 2024 - not by somebody actually seeing one, but by analyzing huge amounts of genetic data from the human gut. This search found 29,959 new RNA sequences, completely different from any known. Thus, we don't know where these things fit into the tree of life!

Biologists found them when they were trying to solve a puzzle. Even smaller than viruses, there exist 'viroids' that are just loops of RNA that cleverly manage to reproduce using the machinery of the cell they infect. Viruses have a protein coat. Viroids are just bare RNA - it doesn't even code for any proteins!

But all known viroids only infect plants. The first one found causes a disease in potatoes; another causes a disease in avocados, and so on. This raised the puzzle: why aren't there viroids that infect bacteria, or animals?

Now perhaps we've found them! But not quite: while obelisks may work in a similar way, they seem genetically unrelated. Also, their RNA seems to code for two proteins.

Given how little we know about this stuff, I think some caution is in order. Still, this is really cool. Do any of you biologists out there know any research going on now to learn more?

The original paper is free to read on the bioRxiv:

• Viroid-like colonists of human microbiomes, https://www.biorxiv.org/content/10.1101/2024.01.20.576352v1.full

I see just one other paper, about an automated system for detecting obelisks:

• Tormentor: An obelisk prediction and annotation pipeline, https://www.biorxiv.org/content/10.1101/2024.05.30.596730v1.full

There's also a budding Wikipedia article on obelisks:

https://en.wikipedia.org/wiki/Obelisk_(biology)

Hat-tip to @metaweta.

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