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Re: How truncation works, and how ranks don't work was Re: Sauropodz r kewl

On Thu, Apr 19, 2012 at 7:11 AM, David Marjanovic
<david.marjanovic@gmx.at> wrote:
> Am 18.04.2012 15:53, schrieb Robert Schenck:
>>  On Wed, Apr 18, 2012 at 9:33 AM, Anthony Docimo <keenir@hotmail.com>
>>  wrote:
> What I do is press Ctrl+U, which shows the source text of the e-mail in a
> new window.

I'm just going to pretend that you cast some kind of conjuring spell to do this.
(but seriously thanks for the informative explanation).

>> > all the extant organisms as closely related to the tuatara as mice
>> > are related to muskrats
>>  In a way we can do that, we can build a phylogenetic tree with
>>  quantified branch lengths, calculate the length from mice to
>>  muskrats, get a number, and then find all taxa at the same difference
>>  from the tuatara. Now, given two researchers, they'll both produce
>>  trees with different branch lengths and thus get different answers.
>>  Hell given two researchers you'll probably get two different tree
>>  topologies too!
> And what do your branch lengths represent? The number of evolutionary
> changes? That depends (to varying degrees) on the dataset you used even if
> you used the same methods to calculate the tree.

Well, it's kinda a silly exercise to begin with, but it seems
reasonable. At least, insofar as your dataset and tree is valid, the
conclusions would be valid. And it'd be a strange person probably who
was able to examine mice and muskrats at the same level of detail as
lizards and tuataras (in order to produce the dataset in the first

>The age of the branch?
> There we get into all the trouble of divergence-dating methods.

What do you see as the troubles with divergence-dating? (not
pretending it's perfect). Also for the purposes of our imaginary
exercise, I think you'd want character change, not time. Of course
combing the two lets us talk about changes in evolutionary rates, but
that's a different matter.

> Not "we have trouble", but "the category of subspecies has been defined in
> several different ways, few of which are ever actually used, and some
> species concepts make subspecies impossible...".

Well, if you want to get all accurate, sure.

> Yep, that was the idea. It would cause enormous upheaval if implemented, and
> it would almost always assign identical ranks to several nested taxa*
Interesting point, something like a Family Rank, nested within a
Family Rank, something for the philosophers to ponder (a puzzle
wrapped up in an enigma).

Robert J. Schenck
Kingsborough Community College
Physical Sciences Department
S332 ph# 718-368-5792
Follow Me on Twitter: @Schenck
KCC Class Schedule on Google Calendar: http://tinyurl.com/mqwlcy