Re: The last ancestor of all life


Marc wrote:
The question about design or evolution of the bacterial flagellum
keeps coming up in Sean Pitman's replies to me so I thought I'd
look at the papers I've seen, but of course I started with a PubMed
search just to see what current results "flagellum evolution" gave.

Now, Sean refuses to accept any papers which use sequence
data comparisons so this message is not going to be of any
interest to him, but *Lurkers* and other interested readers of
talk.origins might consider looking at some of the most recent
papers that came up in my search results - Tom Cavalier-Smith
has two recent publications there, this one available for free...
suggesting the ancestor described in the subject line of this thread:

"Rooting the tree of life by transition analyses."
Biol Direct. 2006 Jul 11;1(1):19 [Epub ahead of print] PMID: 16834776
http://www.biology-direct.com/content/1/1/19
(for the abstract or the accepted paper in draft form, click the link)

and this one would be available to academics, students etc.:

"Cell evolution and Earth history: stasis and revolution."
Philos Trans R Soc Lond B Biol Sci. 2006 Jun 29;361(1470):969-1006.
PMID: 16754610

Abstract:
This synthesis has three main parts. The first discusses the
overall tree of life and nature of the last common ancestor
(cenancestor). I emphasize key steps in cellular evolution
important for ordering and timing the major evolutionary
innovations in the history of the biosphere, explaining especially
the origins of the eukaryote cell and of bacterial flagella and cell
envelope novelties. Second, I map the tree onto the fossil record
and discuss dates of key events and their biogeochemical impact.
Finally, I present a broad synthesis, discussing evidence for a
three-phase history of life. The first phase began perhaps ca 3.5
Gyr ago, when the origin of cells and anoxic photosynthesis
generated the arguably most primitive prokaryote phylum,
Chlorobacteria (= Chloroflexi), the first negibacteria with cells
bounded by two acyl ester phospholipid membranes. After this
'chlorobacterial age' of benthic anaerobic evolution protected
from UV radiation by mineral grains, two momentous quantum
evolutionary episodes of cellular innovation and microbial
radiation dramatically transformed the Earth's surface: the
glycobacterial revolution initiated an oxygenic 'age of cyanobacteria'
and, as the ozone layer grew, the rise of plankton; immensely
later, probably as recently as ca 0.9 Gyr ago, the neomuran
revolution ushered in the 'age of eukaryotes', Archaebacteria
(arguably the youngest bacterial phylum), and morphological
complexity. Diversification of glycobacteria ca 2.8 Gyr ago,
predominantly inhabiting stratified benthic mats, I suggest
caused serial depletion of 13C by ribulose 1,5-bis-phosphate
caboxylase/oxygenase (Rubisco) to yield ultralight late Archaean
organic carbon formerly attributed to methanogenesis plus
methanotrophy. The late origin of archaebacterial methanogenesis
ca 720 Myr ago perhaps triggered snowball Earth episodes by
slight global warming increasing weathering and reducing CO2
levels, to yield runaway cooling; the origin of anaerobic methane
oxidation ca 570 Myr ago reduced methane flux at source, stabilizing
Phanerozoic climates. I argue that the major cellular innovations
exhibit a pattern of quantum evolution followed by very rapid
radiation and then substantial stasis, as described by Simpson.
They yielded organisms that are a mosaic of extremely conservative
and radically novel features, as characterized by De Beer's phrase
'mosaic evolution'. Evolution is not evenly paced and there are
no real molecular clocks.


This is an interesting (free!) paper, although broad brush as
Cavalier-Smith is mostly interested in the very big picture of
bacterial phylogeny.




*****************************

Since this post is a result of looking into recent flagellum reports,
there is another paper worth a look, by Jekely and Arendt:

"Evolution of intraflagellar transport from coated vesicles and
autogenous origin of the eukaryotic cilium."
Bioessays. 2006 Feb;28(2):191-8. PMID: 16435301

Abstract:
The cilium/flagellum is a sensory-motile organelle ancestrally
present in eukaryotic cells. For assembly cilia universally rely
on intraflagellar transport (IFT), a specialised bidirectional
transport process mediated by the ancestral and conserved
IFT complex. Based on the homology of IFT complex proteins
to components of coat protein I (COPI) and clathrin-coated
vesicles, we propose that the non- vesicular, membrane-bound
IFT evolved as a specialised form of coated vesicle transport from
a protocoatomer complex. IFT thus shares common ancestry with
all protocoatomer derivatives, including all vesicle coats and the
nuclear pore complex (NPC). This has major implications for the
evolutionary origin of the cilium. First, it reinforces the tenet that
duplication and divergence of pre-existing structures, rather than
symbiosis, were the major themes during cilium evolution.
Second, it suggests that the initial step in the autogenous origin
of the cilium was the establishment of a membrane patch with
transmembrane proteins transported by the ancestral vesicle-coating
IFT complex. We propose a scenario for how the initial membrane
patch gradually protruded to enhance exposure to the environment,
then started to move, and finally compartmentalised to render
receptor signalling and ciliary beating more efficient.

**********************


This is about the evolutionary origin of the eukaryotic
cilium/flagellum, not the bacterial flagellum. But it is useful and
provides a puzzle piece about what role the Intraflagellar Transport
(IFT) complexes currently play, and might have played in the past.

IIRC Behe disses this paper in the Afterword to the 2006 edition of
Darwin's Black Box. However, we won't be able to get a really detailed
evolution model until we actually understand in detail the structure
and assembly of the mitotic spindle and the centriole, which we are a
long ways from doing. More here:
http://www2.ncseweb.org/kvd/exhibits/immune/immune_evo_bib_long.html

See "The Implications".





So, perhaps I'll get on with the flagellum papers I was going to look
at in another thread or down this thread somewhere, but for now
these papers have caught my attention. (Think of them as "bed time
stories", Sean, bed time for "design" compared with evolution, that
is.)

Oh...
Sean - if you have trouble getting any of these (even the free one),
just go ahead and ask. I'm happy to help.

(signed) marc

.

Relevant Pages

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  • Re: for Sean
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  • Re: The contrast between Sean Pitman and Harlan Bretz
    ... against the real science. ... on "DNA Mutation Rates and Evolution" ... By what Sean put up? ... I gave him several review papers published years after ...
    (talk.origins)
  • Re: for Sean
    ... I have a question for you, Sean. ... The authors of both papers responded to your posts. ... "against" the feasibility of evolution to be kind of silly. ... YOU are too stupid to explain your wonderful mathy sciencey stuff ...
    (talk.origins)
  • Re: The last ancestor of all life
    ... keeps coming up in Sean Pitman's replies to me so I thought I'd ... look at the papers I've seen, but of course I started with a PubMed ... search just to see what current results "flagellum evolution" gave. ... Based on the homology of IFT complex proteins ...
    (talk.origins)
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