Re: Directed Panspermia and Common Descent

"Ernest Major" <{$to$}@meden.demon.co.uk> wrote:
Switch89 <Ryansarcade@xxxxxxxxx> writes
"Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
2. The reason why a universal code seemed more likely to Crick
under the hypothesis of directed panspermia is that Crick thought
that an Earth-derived LUCA would be primitive and would have
a code which wasn't used for many proteins. Whereas he thought
that a code which came from bacteria designed by aliens would
be a mature and frozen code, which would not be capable of
?>> mutating without killing the organism.
[snip]
... On the other hand, what if the
first living thing (not the LUCA) used just a few (say 8-10) amino
acids and then the use of the other amino acids evolved separately in
different lineages? Then the code would be deeply similar, but not
exactly the same.

That's possible. It may even have happened, and the variants been lost
over time. But not all amino-acids are equally suitable for addition at
a particular place in the genetic code, so there would be a tendency for
parallelism to occur in substitutions. (As has happened in the
development of the variant codes from the code of the LUCA.)

Do you have a cite for that? That parallel (convergent) evolution
took place in the evolution of variations on the universal code?

But if aliens seeded life from space, the code would
use 20 or so amino acids and be fully developed. Is that what you're
saying? That makes sense to me. Thanks!

Yep, that is basically what I was suggesting. You are welcome.

.

Relevant Pages

  • Re: Purine World
    ... >>are among the first amino acids, and those live in the same two ... > proteins thought to be present in the LUCA. ... > "Evolution of Amino Acid Frequencies in Proteins Over Deep Time: ... that their proteins do not have modern amino acid relative abundances. ...
    (sci.bio.evolution)
  • Re: Directed Panspermia and Common Descent
    ... that an Earth-derived LUCA would be primitive and would have ... first living thing (not the LUCA) used just a few amino ... The change of AUA from methionine to isoleucine occurred in the mitochondria of echinoderms and flatworms. ... use 20 or so amino acids and be fully developed. ...
    (talk.origins)
  • Re: Directed Panspermia and Common Descent
    ... first living thing (not the LUCA) used just a few amino ... But not all amino-acids are equally suitable for addition at a particular place in the genetic code, so there would be a tendency for parallelism to occur in substitutions. ... (As has happened in the development of the variant codes from the code of the LUCA.) ... use 20 or so amino acids and be fully developed. ...
    (talk.origins)
  • Re: Directed Panspermia and Common Descent
    ... There *are* variants to the universal code. ... mutating without killing the organism. ... It would follow that the LUCA ... also used these twenty amino acids. ...
    (talk.origins)
  • Re: Ribosome origin explained?
    ... evidence-based look at evolution in the RNA world. ... the first solid look at evolution before the LUCA. ... Working backwards is *not* the only way. ...
    (sci.bio.evolution)