classifying life ("primitiveness")

B. J. Tindall bti at DSMZ.DE
Thu Apr 20 15:12:34 CDT 2000

Thanks Ken:
>     For anyone who has not yet done so, I recommend reading the 1995 paper
>by Stanley Miller and Antonio Lazcano ("The Origin of Life---Did It Occur at
>High Temperatures?") in the Journal of Molecular Evolution (Vol.
>41:689-692).  I don't agree with everything they say, but they certainly get
>across the point about how little we really know about the conditions on
>Earth when life originated.  I think it is entirely plausible that the Earth
>could have been a patchwork of large cold areas broken up by hot areas, with
>clines of mesophilic areas in between.  We just don't know, although
>eventually we probably will find evidence that narrows the possibilities.

I will not argue here - and will look up the reference. There was also
something in the same journal recently about the fossil record and
calibrating sequence data - tenor was you can't use sequences to knock the
fossil record if you calibrate sequence rates on fossils.

>     As for inferring thermophilic or non-thermophilic origins from sequence
>data, I suspect we are still at the "toddler" stage on that front.  I think
>Woese has convinced many (including himself) that we are a lot further along
>than we really are, and the extent to which circular reasoning is affecting
>our theories at present will probably amaze us a decade or two down the

We might not agree on other details, but I certainly agree here.

> I predict
>that correctly rooted trees of the future will not have thermophiles (like
>Aquifex, Thermotoga, or the Metabacteria-"Archaebacteria") anywhere near the
>base.  But only time will tell.

But where oh where is the "correct root"? I also think it depends on what
you expect from your "tree" and what it will actually deliver. We had a
nice little session here in Braunschweig and also in Munich recently on
tree topology etc. Quote from one lecturer "if you wear glasses and want to
see exactly the resolution of the system, take off your glasses". I have a
nasty feeling that there are also too many assumptions being built into
computer programs and that the end user just pushes the button and waits
for "the truth" to come out!

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