>Are these problems for creation theories? Some creationists have
>admitted that this presents a problem for explanatory theories of
>design. FWIW, neither Philip Johnson nor Walter ReMine really
>address these questions in their books (_Darwin on Trial_ &
>_The Biotic Message_, respectively), except perhaps to dismiss
>homologies in general.
Walter ReMine does touch on the endosymbiotic theory in his book,
_The biotic message_. But as I mentioned, he does not discuss
its particular implications with respect to creationism in general
or to his own "Message theory". He brings it up as an example of
the "theoretical smorgasborg" of evolutionary ideas but does
not examine the case of endosymbiosis further. With regard to
"transposition" (aka. horizontal transfer) in general, I get the
gist that certain amounts (how much?) of horizontal transfer
might be tolerated by his theory although it might be a fine-line.
It is unclear whether the eubacterial-derived genes found in
these organelles and in the chromosomes of the eukaryotic organisms
possess them is "too much". I believe it is a substantial and
major set of events for many (most?) of the eukaryotic lineages.
Certainly it disrupts the nested hierarchy of genes in eukaryotes
(making them appear polyphyletic).
Walter's concluding statement on endosymbiosis is as follows (p 347):
"Presently, the hypothesis of endosymbiosis remains poorly supported".
I think Walter's conclusion has been out of date for some time.
It is certainly well supported by molecular and biochemical
characterizations and even helped in the discovery of some
introns in eubacteria.
"Molecular evidence has now amply confirmed that mitochondria and
plastids originated as bacterial symbionts. Molecular (particularly
sequence) data have further pin-pointed those contemporary
prokaryotes with which mitochondria and plastids are specifically
affiliated. Two eukaryotic organelles have as their closest living
relatives the eubacteria (Bacteria _sensu_), with plastids originating
from within the blue-green algae (Cyanobacteria) and mitochrondria
from within the alpha-subdivision of the purple bacteria (Proteobacteria).
It is still unclear whether each organelle is the result of a single
endosymbiosis of this type (monophyletic origin), or whether each
arose more than once via prokaryote-eukaryote associations in
difference eukaryotic lineages (polyphyletic origin). [...]"
- Michael W. Gray - Origin and evolution of organelle genomes,
p884, Current Opinion in Genetics and Development 1993 3:844-890.
"The symbiotic origin of chloroplasts and mitochondria has been
generally accepted for a decade or so [reference list deleted], as
has the secondary symbiotic acquisition of the chloroplast by
photosynthetic members of the kingdom Chromista [...]
Acceptance of the symbiotic origins of mitochondria, chloroplasts
and chromist perplastid membranes rests on three lines of argument:
(a) a sufficiently close resemblance between the organelles and
putative potential symbiotic ancestors to make the conversion of
the symbiont to the organelle genetically and developmentally
plausible; (b) the identification of a potential host that entirely
lacks the organelle and its molecular precursors, but which would
have a selective advantage in acquiring it by endosymbiosis;
(c) phylogenetic evidence that clearly demonstrates that the
different organelles actually had a difference ancestor from the
nucleus and the rest of the cytoplasm. Peroxisomes satisfy the
first two criteria but not the third, whereas cilia and nulcei
satisfy none of them. Mitochondria, chloroplasts and the chromist
satisfy all three to such a high degree that no reasonable biologist
seriously doubts their symbiotic origin."
- T. Cavalier-Smith - The number of symbiotic origins of organelles.
pp. 91-21, in Biosystems 1992 28:91-106.
The following references are useful starting points on the subject:
MW Gray & WF Doolittle: Has the endosymbiont hypothesis been proven?
(1982) Microbiol. Rev. 46:1-42
MW Gray: The endosymbiont hypothesis revisited. In _Mitochondrial
Genomes_; Int. Rev. Cytol. (1992) DR Wolstenholme & KW Jeon eds.
141:233-357
Regards, Tim Ikeda (timi@mendel.berkeley.edu)