On Apr 20, 2:29=A0am, Tim Little <t...@[EMAIL PROTECTED]
>
wrote:
> This is the first I'd heard that it was definitely known that it
> evolved only once. =A0What evidence is there for that?
The fact that everything that splits water as a proton source uses the
same enzyme, "Z", to do so? If I have to bet on evolution happening
only once, or happening exactly the same way twice in succession, I'll
go with a single origin.
> If a billion different organisms throughout Earth's span developed a
> primitive capability for oxygenic photosynthesis, and would have been
> successful if they didn't have the competition from more highly
> developed organisms, how would we be able to tell?
True, but there are a whole lot of "leftover" molecular mechanisms
still hanging around in the biosphere currently - in other words,
inferior adaptations often are *not* completely eliminated, but
survive in niche situations. It's not proof, no... but it's is
extremely suggestive.
--
Brian Davis
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