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Re: Breathing

In a message dated 4/17/99 2:43:24 PM EST, ptnorton@email.msn.com writes:

<< I'll open myself up to correction again and ask why an (arguably) close to
 optimal gas exchange sytem (gills), which evolved in a fluid medium that was
 approximately 50% oxygen (H2O), needed to be abandoned for a *less*
 efficient exchange system (the lung) in a medium (the atmosphere) that
 contains *less* than half (21% ?) >>

Gills don't remove the oxygen from the water molecules (which must usually be 
done electrostatically), they remove atmospheric oxygen that is dissolved in 
the water, of which there is far less than 50%(!).