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From: RonO <rokimoto557@gmail.com>
Newsgroups: talk.origins
Subject: Re: Last universal but not universal common ancestor of life
Date: Sat, 7 Jun 2025 08:53:39 -0500
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On 6/6/2025 5:09 PM, JTEM wrote:
> 
> Maybe it's just badly written, but it's as near to
> gibberish as anything I've ever seen from this
> source:
> 
> https://www.popularmechanics.com/science/a64969200/amino-acids-origin- 
> of-life-order/?utm_source=social&utm_medium=copy&utm_campaign=action_bar
> 
> First off, by "Universal common ancestor" they just mean
> the "Common ancestor for life on earth."
> 
> The popular belief is "Common Descent," as you should be
> aware, and this implies (or requires) all of life to trace
> back to a single point, a single ancestor.
> 
> "Universal Ancestor" would be the ancestor of all life in
> the universe, which if this piece is talking about then it
> is entirely rubbish...
> 
> First off, I do NOT believe there ever was a single source
> for life on earth. This would imply that there's only a
> single way for abiogenesis to occur, AND that it only could
> happen once.
> 
> Fact is, it could have happened dozens of times. I mean,
> one defining characteristic of science is repeatability. So
> if conditions are right, it should happen. Period. And if
> conditions are not right, it should not happen. Period.
> 
> There is a way around this, yes. You can say that Panspermia
> is the right answer, that life emerged however soon after the
> Big Bang it could come about, and from there rained down on
> worlds... which brings us to ANOTHER complaint of mine.
> 
> And here I do quote:
> 
> Our understanding of these extremely ancient times will always
> be incomplete, but it’s important for us to keep researching
> early Earth.
> 
> My issue here is that it's not really about time. It's not
> about time at all.
> 
> If anything rained down on the earth from space, undoubtedly
> more is this magic pixie dust still exists. We can find it.
> We can study it.
> 
> The conditions of the early earth can be determined to a
> greater and greater extant. We'll probably find models in
> other worlds.
> 
> I guess what I'm saying is that it's not about time it's
> about conditions. Right now we have ZERO clue under which
> conditions life will form, nor even if it can spontaneously
> form. If we can answer these questions we'll have everything
> we need to reconstruct the origins of life on earth.

https://www.pnas.org/doi/epub/10.1073/pnas.2410311121

The last universal common ancestor discussed in the PNAS article that is 
discussed in the Popular Mechanics article is just the last common 
ancestor (LUCA) of all extant life on earth.  This would be the common 
ancestor of archaea and eubacteria.  The PNAS article thinks that they 
can acquire information about life that existed before LUCA by looking 
at the amino acids used in protein domains that would have existed in 
pre LUCA lifeforms.  They tried to figure out the amino acid composition 
of the protein domains that have likely existed since the first proteins 
were evolving to be functional.  The initial genetic code would have had 
to make these ancient protein domains.  They claim to have estimated the 
frequency of use of each of the 20 amino acids before and after LUCA.

They think that the order that the amino acids were added to the genetic 
code needs to be reevaluated, and should reflect pre LUCA rather than 
post LUCA amino acid use.  Probably the main issue with their 
assumptions is that these protein domains have been conserved because 
they are the best sequences for the job that they do.  They make very 
stable alpha helices and beta pleated sheets that fold up into the same 
3D structure with a high degree of reproducibility.  The then existing 
genetic code would have likely been designating for more than the amino 
acids that turned out to be the best for particular jobs.  What they 
might be observing would have had to have been selection post 
development of a genetic code to encode these particular amino acids 
more accurately.

As a side note, the article was edited by Doolittle.  So Doolittle is 
still alive and kicking, and still a member of the National Academy.  TO 
ancients may recall Doolittle as one of the early Science side 
combatants in the scientific creationist fiasco that resulted in the 
creation of talk.origins.

Ron Okimoto