The evidence they present, however, suggests to me that “homology” is being stretched well past its limits as a descriptor. I take your point, however.
This paper by Woese and colleagues argues for bona fide non-homologous ribosomal proteins:
That’s all interesting information in it’s own right, and sheds some tiny sliver of light on those very early phases of cellular and perhaps translation system evolution in the history of life.
It doesn’t really serve as an argument to cast doubt on the inference that the common genetic code, and the many homologous molecules that carry out translation of the code, is bona fide evidence for common descent. Not sure if you’re even trying to argue that it does.
It is entirely possible that the ribosome itself had not at all “finished” evolving by the time the bacterial and archaeal lineages split (and that it is still evolving under both positive and purifying selection), and that RNA and protein components continued accreting, or even became replaced independently in both lineages. It is even plausible there is some convergence in what constituents were altered, and how.
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I believe that’s the relevant part of the sentence, accent on the “me”.
Now that one works. Of course there’s no surprise that some ribosomal protons are not homologous between domains.
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I know this isn’t necessary for this audience, but I find that it helps to keep my eyes “on the prize”, as it were:
It’s OK to be talking about the gold, and certainly these molecules inform on function and evolution, but they aren’t the more important players here. It’s the RNA, they grey parts of the complex, that are the keys to function, indeed to life itself.
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I disagree. Multicellularity, in the red-algaea-sense, with differentiated cell types, is hard. Cancer is a classic reminder of what happens in a multicellular organism when the tight regulation of cells fails.
Bacteria have existed and been evolving for billions of years, but the bacterial cell architecture never gave rise to anything resembling, say, a red algaea.
As you yourself said: “If you want something that might eventually become multicellular, the smart money based on the evolutionary record is that you need to have it be a eukaryote from the start …”
Again, one must ask where you could be going with this. Life didn’t start with eukaryotes. Even in eukaryotes, multicellularity seems to have been an unlikely event. And if eukaryotes are not first, you have to propose that life was designed to produce eukaryotes. How would it be possible either to require or forbid such a development?
But the business part, the enzymatic center, the ribozyme, is highly homologous.
As a leading ID theorist, what’s your hypothesis that explains the Designer’s use of a ribozyme for such an important function?
And what empirical predictions does it make?
So? None of those proteins contain the core ribozyme’s enzymatic activity of peptidyl transferase. Evolution could only work around the ribozyme, redecorating around it if you will.
An intelligent designer would be under no such constraints.
How do you explain that, as a leading ID theorist, instead of dancing around it?
And leading ID theorists can’t even begin to explain that.
Best to just pretend that ribozyme at the center of the ribosome and at the center of life doesn’t even exist, right @pnelson?
Not nice @John_Harshman. Do not pounce on him. He is trying to learn.
I’m not sure how it is hard. I though it was actually easy!
One man’s pounce is another man’s education. What @purposenation calls “pouncing” is just explaining the problems with a scenario. I call that a service to the pouncee.
Are you referring to your personal case? The journey from zygote to adult may have been easy for you, but understand that around 1/3 of zygotes don’t make it. I’ve also seen a person claim that the hardest thing they ever did in their life was gastrulation.
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Agreed. I’ve been embarrassed a few times on forums. But that’s how I’ve learned and corrected myself. If I say something stupid I want to know.
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Dunno about that – I think rRNA is pretty cool:
"Although rRNA may have originated in a hypothetical pre-protein RNA world—the most common explanation for why ribosomes contain so much RNA—it is not necessary to invoke such explanations based on ‘frozen accidents’ in evolution. In addition to its many specific roles, rRNA serves a fundamental purpose in ribosomes by providing appropriate dimensions and an assembly backbone at a ribosome-sequestration cost that is two orders of magnitude lower than would be possible using protein.”
From here:
https://www.nature.com/articles/nature22998
The other thing (well – one other thing, anyway) to realize about rRNA is the enormous protein-based machine which assembles the RNA core of the large subunit. Ann Gauger likes to talk about “causal circularity” at the heart of life (i.e., to make X, you need X) and this is causal circularity with bells on, balloons, a marching band, and the beautiful blond waving from a convertible. I’m on my way out of the door to run Sunday errands, but if I can find the citation later today, I’ll post it in this thread.
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Great. Do you ever cite any data, or do you only note what words are used?
Don’t theorists start with data?
Found the paper, which applies only to eukaryotic ribosomal assembly:
Art,
This talk by Loren Williams, which I listened to while cooking a complicated meal a while back, is really first-rate:
You’ll see that at about 55:00 into his presentation, close to the end, Williams makes a point very close to Ann’s “causal circularity” insight (in this case, Williams is talking about the interdependence of RNA and protein). Nothing in Williams’s published work, however, shows how rRNA could function without the assistance of protein.
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The main thing is whether you have an ID hypothesis explaining why the enzymatic core of the ribosome is a ribozyme.
I guess the first report I knew of that suggested this was the paper by Noller et al.
I haven’t listened to the talk, but Williams’ papers do not refer to this seeming causality as a problem. Rather, they talk about (in a manner of speaking) cycles in which one or the other (RNA or peptide) push along a reiterative evolutionary process, from simple to elaborate.
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