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Comment by borissk | Hacker News Reader

The origin of eukaryotes is an amazing story. The chances of survival of the original combined organism were 0.0000000001%. All the bacterial RNA and DNA that the bacteria produced during life and death were surely messing up with the archaea inner workings, as bacteria and archaea have different genetic code "dialects". The archea had to evolve a nucleus instantly to keep the bacterial RNA away from it's ribosomes.

The survival of eukaryotes may be so unlikely as to even partially explain Fermi paradox.

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> The archea had to evolve a nucleus instantly to keep the bacterial RNA away from it's ribosomes.

I heard another theory that it was actually the archea that engulfed the pre-mitochondria rather than the it accidentally finding itself inside an archea. There's some kinds of archea that occasionally grow some extracellular "appendages" and it's conjectured that it may have had some kind of more typical symbiotic relationship with the two kinds of microbes living in near physical contact. What could have happened is that the archea gradually came to fully engulf the protomitochonria with the appendages evolving into being the full body of modern eukaryotes with the nucleus evolving from the functions that were part of the main archean cell body. Some functions got shuffled between the three compartments as this became more of an obligate relationship.

Nick Lane wrote some amazing popular science books on the history of mitochondria;

- Power, Sex, Suicide for a general overview and history of mitochondria (did you know that Lynn Margulis, main proponent of the endosymbiont theory, was once married to Carl Sagan?!?)

- The Vital Question on restraints on life due to the biochemistry of mitochondria

Both highly, highly recommended.

Every single one of his books is amazing and mind blowing. His latest "Transformers" on the krebb cycle is a must read if you're interested in the origins of life.

The theory that eukaryotic cells are just a bunch of bacterial subsystems that happened to start cooperating is one of the cooler points in the biology iceberg. Up there with chickens descended from the T Rex for me.

You'd love the highly influential 2015 paper, Major evolutionary transitions in individuality

https://www.pnas.org/doi/full/10.1073/pnas.1421402112

> The evolution of life on earth has been driven by a small number of major evolutionary transitions. These transitions have been characterized by individuals that could previously replicate independently, cooperating to form a new, more complex life form. For example, [...]

> Up there with chickens descended from the T Rex for me.

Archaeopteryx lived in the Jurassic, so it's not really possible that chicken descended from the T Rex. They're cousins though.

Actually, Archaeopteryx is not an ancestor to chickens either...

Archaeopteryx is offshoot in the evolutionary path leading to birds. It shares a common ancestor with modern birds but branched off in a direction that did not lead directly to them.

The Great Chicken God decries your heresy!

> The chances of survival of the original combined organism were 0.0000000001%.

It was surely an experiment attempted many times, as countless bacteria infected countless protoeukaryotes. Probably doesn't explain Fermi paradox, as it succeeded at least twice here on Earth. One for mitochondria, another for chloroplasts.

The symbiosis with chloroplasts was a lot easier, as the host already had a nucleus.

Sceptical of this. Where did that number come from? What's the uncertainty? Yes, it's an extremely unlikely event, but unlikely events happen all the time. There's just as good an argument that given the advantages conferred by the union, it's bound to be successful given enough iterations.

I mean, it happened again with chloroplasts and there's a bunch of other cases of endosymbiosis too it's not that rare

Making it happen once is harder than doing it a second time. Plant cells have both mitochondria and chloroplasts.

I'm unfamiliar with research into the difficulty of the second endosymbiotic event that no humans were present to measure and analyze being reduced by the existence of a first endosymbiotic event that has also not been replicated in a lab yet, resulting in another n=1 data point

I think this might count as endosymbiosis replicated in a lab: https://pubmed.ncbi.nlm.nih.gov/30373839/

It's a system to measure endosymbiosis in an organism that's already undergone endosymbiosis so not directly applicable for the entirety of gp's hypothesis, but there's definitely a ton of research into it. There'll always remain a question of if we engineer a system does that work the same way as the evolutionary path since we have the benefit of being non-random/guided by intelligence. It's like with abiogenesis, if we ever figure out a system that lets us reproducibly create life within the timespan of a couple years so we can replicate it and study it reasonably that system almost certainly isn't the original way it happened, but it'll give us good insights into the concepts hopefully

In order to protect its genome from the mitochondrial genome, the host cell had to evolve the nucleus and possibly also sexual reproduction. Once that's done, it works just as well for the chloroplast.

The nucleus is also considered a potential candidate for endosymbiosis [1] and I'd really love to see some actual evidence for your claims at some point instead of just vague handwaving

(1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571569

I appreciate you for calling out the number. It’s ok to say “vanishingly minuscule”. A number may seem insignificant but what was presented was actually precise.

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