On Wed, 19 May 2004 15:31:00 +0000 (UTC), Joost Vrielink
 wrote:

>Hi,
>
>As I understand it, DNA is used for development/replication in all life 
>forms. Natural selection would imply that it is the 'best' way to do 
>this (not stating all this as fact, just my perception so correct me if 
>I'm wrong). Some questions that I can't seem to find the answer to:
>
>Are there any other known frameworks similar to DNA used maybe in the 
>earlier stages of evolution or didn't 'life' start until DNA was 
>synthesized randomly? Did DNA evolve from a simpler replication system?
>
>Since DNA is basically the same in all life forms and has been for 
>millions of years, can it be expected that it will not be replaced by 
>something else in the future? In other words, is it perfect for 
>sustaining life?
>
>Thanks for any answers or pointers,
>

The fact that DNA seems to be the almost universal system for encoding
genetic information in no way suggests that it is"perfect for
sustaining life" or that it is the "best" way to do it.  It only
suggests that it is an effective way that ending up being used by
those probably gene-sharing protocells that ended up being the
ancestors of all living things.  Certainly it is so well entrenched
into the molecular biological machinery (and has been for several
billions of years) that it is virtually certain not to be replaced.

Many people think that RNA coding may have preceded DNA. The fact that
RNA can act as enzymes and as structural components does suggest that
an RNA world could have preceded even the coding of proteins. In any
case, the ability to form double stranded structures with base pairing
does produce, as Watson and Crick so famously pointed out many decades
ago, a very nice mechanism for information copying.  

There don't seem to be any other candidates for such complex
information storage, duplication, and retrieval as the DNA/RNA system.
Still, that doesn't mean it is "perfect".
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