In article ,
Maarten D. de Jong  wrote:
>
>During a discussion about primitive forms of life, someone popped the ques-
>tion why there is so little biochemical variation around. His argument ran
>that most life on Earth has some form of DNA or RNA inside it, and that there
>is little evidence for anything more primitive. He then proceeded to say that
>regular biological evolution breaks down at the biochemical level, and that 
>you would need a different theory (but not any form of creationism, he was 
>quite emphatic about that) in order to explain all sorts of basic biological
>structures, like for example DNA.

I am not a biologist, but Archea show far more fundamental variation in
chemistry than Bacteria or Eukaria, both in the types of chemical reactions
they can cause and/or exploit, and in the substances that they are made
of.  They do however use DNA and RNA.

I would make the point that since DNA is how we identify life forms and
the relationships between them, anything more primitive goes unnoticed.
Some theories involve some form of self-replicating structures before
DNA was developed, incorporated, enslaved, whatever; how would we trace
the lineage of whatever that was with the tools we currently have?  If
there are still pre-DNA life forms living in volcanic vents somewhere,
perhaps being gobbled up by DNA-bearing cells, would we know?  Any samples
of slime scraped off of the rocks would be examined for things that look
like cells, and tested for DNA; unless you were specifically looking for
it, would anyone notice anything simpler?  Only after something like that
was discovered might we recognize that some structures in modern cells are
descendents of that earlier life.

When looking at a drop of pond water through a microscope, how many
floating bits of crud do you ignore while looking for unicellular
organisms?  Does anyone know or care what most of those bits of crud
are?  Heck, only a small fraction of the microrganisms that *do* have
DNA have been studied.  Who knows what is going on in front of (or
inside of) our noses?

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