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lukeprog comments on The Octopus, the Dolphin and Us: a Great Filter tale - Less Wrong
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One theory gaining support recently is that the transition from prokaryote to eukaryote was damned hard, so that seems like a decent candidate given our limited knowledge today.
If the current model - merger of multiple prokaryotes - is correct, then the linked article (which says "And in more than 3 billion years of existence, it happened exactly once.") is incorrect. Nuclei, mitochondria, and cholorplasts represent 3 distinct merger events here on Earth. Actually, the article even mentions nuclei, mitochondria, and chloroplasts all being likely endosymbionts, then goes and repeats the claim of uniqueness.
In any case, if it can happen 3 times on one planet, it probably isn't dramatically unlikely, especially since at least one of those three events (chloroplasts) is strictly unnecessary for intelligence (in that no known intelligent species possesses them).
Wait, nuclei? Link?
Where's the host's DNA, then?
That's a version of the "chimeric theory", one of a few for the origin of eukaryotic organization: see Wikipedia's article. The DNA of the host cell would have migrated into the encapsulated bacterium or archaeon, through processes that I'll admit I'm a bit fuzzy on.
(Wikipedia links several papers in support of this theory; the only un-paywalled one I could find, however, is Margulis et al. 2000.)
Huh. I've skimmed this a few times and it's pretty hard to understand... so they are saying that the nucleus ancestor was a fast swimming oxygen avoider, and it basically chose to avoid oxygen by hiding inside another cell like a hermit crab - and in exchange, pushing the "shell" cell around...and eventually fusing genomes with it?
I wasn't proposing the merger of multiple prokaryotes as a candidate for Great Filter, I was proposing the transition from prokaryote to eukaryote as a candidate for Great Filter.