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Re: starship-design: Re: Aliens, why haven't they contact us?

> From: jimaclem@juno.com
> Just a thought to consider folks.  All living organisms on this planet,
> including viruses have DNA and RNA constructed from the same four
> proteins, 
The components listed below are not proteins, but base
components of nucleotides that are segments of DNA and RNA.
They code for sequences of amino acids that finally
constitute proteins.

> adenine, cytosine, guanine and tyrosine.  
In DNA occur: adenine, cytosine, guanine, and thymine;
in RNA occur: adenine, cytosine, guanine, and uracil.
Tyrosine is an amino acid and hence is a component of proteins.

> (And I do mean ALL
> life forms on this planet, from viruses to trees to us).  The chances
> that an alien microbe, or anything else, would use these same proteins
> seem rather small, thus rendering them and us relatively harmless to each
> other since we cant read each other's cellular codes.
The harm from microbes does not come from reading our
cellular codes. The two main sorces of harm are:
- eating vital components of our bodies (e.g., cellular
  membranes, cellular proteins), hence disrupting 
  their functioning;
- releasing waste substances that have toxic (disrupting) effects
  on biochemical pathways in our cells.

Both types of harm can be inflicted by alien microbes, if only
they are able to survive in the environment of our organisms, 
which requires:
- being resistant to disruptive (toxic, immune-action)
  influences from substances and enzymes in our cells,
- being able to "eat" (metabolize) substances (e.g., proteins)
  occuring within our bodies.
For the alien bacteria to be able to do that, it does not
have to have even remotely similar biochemistry to ours,
not speaking about the same genetic code...
E.g., microbes living on oceanic vents metabolize
and thrive on inorganic substances (mostly toxic to us humans),
which substances have quite different composition and chemistry
than the biochemistry of the microbe bodies.

Hence, little can be said IN GENERAL about possible
effects of alien microbes on our planet unless SOMETHING
more specific is known about their (bio)chemistry.

However, from the general knowledge about requirements
of very precise tuning of two chemistries in order to made
them immune to each other influences follows that it is very
improbable for them NOT to interact chemically.
And such interaction is most probable to DISRUPT
biochemical workings in BOTH sides. Hence, the most
probable effect would be that we and aliens are
MUTUALLY TOXIC, hence the one with less numbers
of organisms within the contact area will perish, 
possibly doing before that considerable damage to the other 
(remember "War of the Worlds"...).
With full clash of comparatively similar number of organisms,
BOTH sides may perish (or be significantly damaged, beyond
repair of their original environment).

-- Zenon