What if the key sequence of mutations developed in a prokaryote that gave
rise to what is now the eukaryotic cell-plasm, but that various descendants
of this "swallower" prokaryote then adopted a large number of different
prokaryotes as proto-nuclei? Is it possible that multiple independent
origins (perhaps thousands or millions, once the essential "swallowing"
mutations had developed) could account for the observed variation in
eukaryotic rRNAs?
Note that amoebas seem to be capable of sustaining new digestion-resistant
prokaryotic parasites within their cell-plasms even now, so multiple
independent eukaryotic origins doesn't seem too implausible to me.
If the idea of multiple independent origins is correct, then I think we'd
*expect* to see as much variation among eukaryotes as we see among
prokaryotes, even if the eukaryotes have only existed for a much shorter
time, because eukaryotic genes would arise from a broad sampling of
prokaryotic genes.
This stuff is on the edge of my ability to think about intelligibly, so
please pardon me if I made any really heinous mistakes.
Eric Watt Forste <arkuat@pobox.com> http://www.c2.org/~arkuat/