DNAunion: In reply to Chris Cogan's "Re: WHY DOES THE UNIVERSE WORK" reply
posted 10/16/2000.
>>Chirs: ...and we know that automobile engines do *not* reproduce
themselves.
>>DNAunion: We also know that prebiotic molecules do NOT reproduce
themselves.
>>Chris: *This* is false. Even something so simple as a water molecule can
reproduce itself under suitable circumstances.
DNAunion: Uhm, okay, well maybe, if you insist - got a reference to support
this?
>>Chris: Further, molecules have even been observe to evolve (although only
slightly in the experiments I read about).
DNAunion: I will assume you are referring to in vitro evolution. It would
depend on the actual experiment under consideration as they are not conducted
under purely-natural conditions: but this is not an issue in some/many/most
cases. I agree that molecules can evolve in such experiments, but is it
"natural", "directed", or a little of both. Using PCR instead of normal
reproduction seems valid enough (for me anyway: and note we are not talking
here about abiogenesis, but life's subsequent evolution). But the intense
selection mechanisms - where all attributes of the molecules are ignored
except for affinity to a pre-specified template - seems unnatural. The
question would be, is this selection's "unnaturalness" meaningful? If it
just speeds up what would occur under natural conditions (as PCR does), then
there should be no objection, in my view. However, I do not feel that this
is the case: I feel that the selection methods used in in vitro evolution
experiments produces results other than those that would occur in nature
(furthermore, there are specific, pre-determined, fixed goals that are aimed
for from step one). Again, I am not stating that these issues necessarily
invalidate the (natural) evolution in in vitro evolution, but I think the
topic should be discussed further. (Also, note that I don't deny that
evolution occurs in nature, nor that it does not occur in molecules like
nucleic acids: I am just asking whether or not in vitro experiments are
actually valid models of NATURAL evolution).
>>Chris: I should add that, *strictly* speaking, probably no molecules
actually reproduce themselves.
DNAunion: Actually, there are some. But they were designed and are not
self-sustaining. One example is the "famous" self-replicating 32-amino-acid
peptide. Given its 15- and 17amino-acid subparts, it could serve as a
template and could catalyze the joining of the 2 subparts into a new copy:
but the full 32-aa peptide could not form its own subparts (researchers had
to supply them), so although it was self-replicating, it was not
self-sustaining. Some very-short "replicating" RNAs have also been designed.
However, naturally-occurring RNA does not reproduce itself (no RNA-dependent
RNA-polymerase has ever been recovered in prebiotic experiments).
>>Chris: DNA does not reproduce itself, for example. It is reproduced, but
not by itself. It is, as Lewontin and others have pointed out, passive.
DNAunion: Okay, so how was I wrong? Sorry but the "strictly" part is
irrelevant: water does not reproduce, and neither does "prebiotic" RNA (no
technicality involved).
[…]
This archive was generated by hypermail 2b29 : Sat Oct 21 2000 - 06:48:24 EDT