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On the question of whether new techniques give us a more precise and
justifiable way to answer "Are these trees significantly different",

and the related issue of whether any theories within the "theropod theory"
class can be considered to be significantly different, we should perhaps
consider the difference between a representative BAMM tree, and my 2F

(Of course, I believe we don't have enough info to put quite so much detail
into mine), but the question is very similar to asking:

  Does the structure:

    {Henry VIII was Henry VII's son, and they were both some kind of
descendant of Henry VI}

...differ significantly from the structure:

    {Henry VI was Henry VII's son, and they were both some kind of
descendant of Henry VIII}.

I think it depends on what you consider to be an important difference.

Here's another question:  If the difference is so unimportant, why is the
"general theropod theory tree" only ever been presented in non-2F form?

Also, why do the majority of dinobird trees/cladograms usually concentrate
on the structure *within* the dinobird clade, and not on the more basal
structures way back into the Triassic?

The reason is that people *do* believe the difference is significant.  This
isn't really surprising, since most historians would consider it a major
event if the entire tree of royal descent were to remain the same except
that Henry VII and Henry VIII were shown to have descended in the reverse
order to conventional belief.

And if the major tenets of the conventional views of bird, arcto & mani
descent are true, then I'm a monkey's uncle.

However, I can't help wondering whether this "Is it really different"
business, is just a way for the mainstream to forge a bridge across to 2F!,
just as evolution, in some way seems to seek some dimension through which it
can ride downhill all the way to some relatively inaccessible potential
"well" apparently on the other side of a ridge of hills.  It's like the
Romans building a ramp up to the fortress of Massada, only this time, when
they get there, they will claim no-one had ever been there before!  We
cameramen, porters etc who were actually the first to get there will be
dismissed with "They were right, but for the wrong reasons".

There will always be some trees for which just a single change will
represent a fundamental difference, and no amount of sophistry will ever be
able to change that fact.



--Orig. Message -- From: chris brochu <cbrochu@fmppr.fmnh.org>
Date: Wed, 31 Mar 1999 13:19:26 -0600

>John V Jackson wrote:
>> --Orig. Message-- From: chris brochu <cbrochu@fmppr.fmnh.org>
>> Date: Sun, 28 Mar 1999 12:06:57 -0600
>> >John V Jackson wrote:
>> >
>> >>>[Matt T:] "It is hard to deny the power of the theropod hypothesis,
>> >
>> >> People often cast the issue in the form of "theropod" vs
>> >> but there is more than one theropod theory, and most are mutually
>> >> exclusive.  In some ways, all the wrong theories have more in common
>> >>with each other than with the truth.
>> >
>> >But ARE these "mutually exclusive?"  There are quantitative ways of
>> >addressing that question.  The days when we could simply step back and
>> >say "Wow - those trees are, like, really different and stuff" are long
>> over.
>> The quantitative procedures for comparing them will depend entirely on
>> processes that created them.
>No - we're not comparing robustness, or the quality of the trees in any
>way.  We're only addressing the question, "are these trees of a
>fundamentally different shape."  It doesn't matter if we're comparing
>trees generated cladistically, phenetically, from stratigraphy, from
>maximum likelihood, or from a seance.
>>The statistical algorithms used will have
>> confidences associable with each feature of a tree or clad, but what if
>> trees were generated in some other way?
>I think you're confusing measures of tree support with measures of
>incongruence.  Measures of support will certainly depend on the method
>of obtaining them, but if I'm only interested if two trees are
>fundamentally different, it doesn't matter how we came to acquire them.
>> >It is generally thought that highly congruent results from disparate
>> >sources suggest an approximation of truth.  But, we don't necessarily
>> >expect different data sets to yield precisely identical signals -
>> Rough clusters around a target are to be expected, but though precision
>> not expected from every shot, the average of all the shots might be
>> to have some significance if the weapon is "true enough".  No-one ever
>> near my bullseye though!
>But the weapons aren't always the same.  For most systematists, failure
>to obtain the preferred result means one should reconsider the preferred