prokaryote evolution and globin proteins

B.J.Tindall bti at DSMZ.DE
Wed Oct 23 10:35:59 CDT 2002


Ken Kinman wrote:
>      As for photosynthesis based on H2S rather than H2O, I believe it to be
>a secondary development, and that most photoautotrophs have used water from
>the beginning.  And for those of you who might be unaware of it, it has been
>demonstrated that oxygenic photosynthesis only requires a single photosystem
>(even though most forms now use the complicated system with both
>photosystems I and II).
>
Ah, but the sulphide based systems also only use one photosystem. The other
question is how do you prove that something is "primitive" (i.e. in its
original state) or "secondarily simplified to look like the primitive
form". Perhaps "belief" is the best answer ;-). From an evolutionary point
of view the single photosystem H2S based system is more widely distributed
across the evolutionary tree. The bias twoards H20 is based largely on the
cyanobacteria and the fact that all eukaryotic photoautotrophs seem to have
"taken a cyanobacterium captive". Ah well that's half the fun of healthy
speculation I suppose.
Thanks also for the link.
Brian

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