[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: The Drunken Sailor's Stumble (was Re: March of "progress")




David,
I'm not going to argue with you about Gould's ideas. He's a bright scientist, but some of his ideas are too simplistic in my view (Simon Conway-Morris rightly criticizes some of these; see Crucible of Creation). The most troublesome is that the so-called Cambrian "explosion" was supposedly a phyletic explosion of body-plans, when it is more realistically regarded as an explosion of hard parts scattered here and there on an already well-diversified Metazoan tree. But you are right that multicellularity need not evolve (it probably didn't on Mars), but it obviously did on Earth many different times.
And "jumping genes"----of course horizontal gene transfer is a real phenomenon. The point is that the super-rampant level of such transfers (which Woese is now leaning on) occurred extremely early in eubacterial evolution and had undoubtedly calmed down considerably before the metabacterial stage, and it is rare (in comparison) amongst eukaryotes. Genes can jump from Kingdom to Kingdom, but I believe Woese is greatly exaggerating its importance compared to vertical inheritance (even among the bacteria).
Another exaggeration is the gap between Eubacteria and Metabacteria (aka Archaea), which is shrinking very rapidly. Read Ernst Mayr's criticisms of Woese's paradigm in Proceedings of the National Academy of Sciences (September 1998). Noone is denying that Metabacteria and Eukaryota are related, but if you raise Metabacteria to Domain status, then cladistically you would have to recognize many different Domains of eubacteria.
Ribosomal gene "trees" can be very misleading, and they erroneously placed microsporidians among other amitochondriate protists far too deeply in the eukaryotic tree. It took tubulins gene sequences and heat shock protein sequences to show that they were "degenerate" eumycotans (and in retrospect this has been further confirmed by morphological characteristics as well). Woese is an intelligent scientist, but in my opinion he is not even in the same league as Ernst Mayr, much less Thomas Cavalier-Smith (probably the world's brightest biologist, although less well-known).
-----Ken
*******************************************************
From: "David Marjanovic" <david.marjanovic@gmx.at>
Reply-To: david.marjanovic@gmx.at
To: "The Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: The Drunken Sailor's Stumble (was Re: March of "progress")
Date: Mon, 5 Mar 2001 00:17:26 +0100

----- Original Message -----
From: "Ken Kinman" <kinman@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Sunday, March 04, 2001 8:50 PM
Subject: March of "progress"


> Tim,
> The old "march of progress" idea is criticized mainly because progress
> is such a loaded word (just like "superior" is a loaded word).
> But it does reflect the directionality of evolution, certainly in the
> time dimension, and often in complexity as well (although the latter is
> somewhat reversible, as in Mesozoans, pentastomid "worm" crustaceans, and
> parasites in general). Single cells must precede multicellularity.
> Amphibians and reptiles had to precede birds and mammals. [and I strongly
> believe Eubacteria were around almost a billion years before giving rise to
> the Metabacteria-Eukaryota clade].


Stephen J. Gould, in his IMHO excellent book "Full House", makes a very good
case against this. He writes that if you plot the complexity of life on the
x axis against the number of species (or, probably, individuals or whatever)
on the y axis, a distorted Gauss curve will emerge; distorted because there
is a "left wall", the minimal complexity of life, to the left of which there
are only viruses, but apparently no "right wall". Life began near or at the
left wall and has been filling all the available space; there is probably an
equal probability that a species will be more vs. less complex than its
ancestor (though there is a selection pressure for decreasing complexity,
the evolution of parasitism, but apparently no such universal one for
increasing complexity, so it might be on the whole more probable that
descendants are less complex). Single cells must indeed precede
multicellularity and so on, but multicellularity etc. _need_ not evolve.


[so all you think is wrong about the 3 domains is the failure to find that
(Eu)bacteria is paraphyletic?]

>      So because of this directionality

which only appears a posteriori, and even then only if one overlooks the bulk of life, bacteria,

[...]
>      Life on Earth (Geobiota) is optimally divided into a handful of
> Kingdoms (about 4-6),

Optimally? Why?

> and everyone's education should include a basic
> understanding of their relationships.

I agree.

[...]
> The confusion it is generating
> is just a tip of the iceberg, and the now overused crutch of ad hoc
> "horizontal gene transfer" is just sweeping the confusion under the rug.

Horizontal/lateral gene transfer is a real phenomenon, and often it is
detectable. It is probably always tempting to us it as an ad hoc crutch, but
it happens. An hour ago I cited "Natura non facit saltus", but genes can and
do make quite big jumps at times.


> But just one simple step-----Stop using "Archaea" as outgroup to
> Eubacteria-----would go a long way to mitigating the mess (and the name
> "Archaea" is helping to perpetuate such misrooting). That has been my main
> message to bacteriologists all along, whether they believe my other ideas or
> not.


Erm... are there any bacteriologists on this list?

> Otherwise medicine, agriculture, and other important fields (that
> depend on accurate bacterial phylogenies)

Not being a bacteriologist, I can't imagine... how?

****************************
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com