[Taxacom] New systematics book

[JF Mate]

Curtis Clark wrote:

"This would leave us with a taxonomy defined by what we don't know, which
would be travesty beyond measure."

I recognize taxons A and B because there is a ´gap´, the result of the
extinction of populations and ultimately the genetic isolation (by whatever
means) of two metapopulations. Fill in the gap with our back-from-the-dead
extinct populations and you don´t really have an objective way of saying
this is taxon A and this taxon B. I am not saying this thought experiment
has any practical value beyond filling TAXACOM´s bloated inbox. I am just
pushing the argument to draw attention to the inherent subjectivity.

"One point of grouping by synapomorphy is that one can have groups in the
absence of gaps. And a purpose for studying speciation is to understand
species as evolutionary units (my favorite definition of phylogeny is
"genealogy of species")."

Ultimately you can find differences between populations or even within
them. Me and my family have a peculiar clubbed second toe. Every blood
relation that I have looked at has this trait and as far as I have seen
(politely, people don´t like to have their feet checked) it is limited to
my relations (my sample is only hundreds, I am not making any claims, it is
just an example). Obviously this synapomorphy does not make us a distinct
species but, should all humanity become extinct but us, that trait will
become one of the defining synapomorphies (behold their mishappen toe!). Or
how about lactose tolerance or the picanthic fold in eastern Asia? It is
the extinction of gaps that eliminates the gradations and make us
comfortable with often random, inherited changes (synapomorphies).

"In general, transitional forms are statistically insignificant. Remember
that punctuated equilibrium was the application of peripatric speciation to
the fossil record, and it was an explanation for the paucity of
transitional forms."

SJG would have loved it of course! I am not very keen on it but then again
it is a personal opinion. Small developmental changes can lead to major
(noticeable) morphological ones. At the same time unseen or unrecorded
changes in a species metabolism can have profound effects on a species
survival, often beyond anything afforded by morphology (i.e. tolerance to
anoxia or heavy metals). Measuring change from one angle (gross morphology)
underestimates the real change (whole genome) of lineages through time.
Alas, that is the nature of fossils.

Ken Kinman wrote:
"By the way, if I could have lived in the Jurassic, I would have probably
classified birds as just a peculiar family of dinosaurs in Class Reptilia.
In the Cretaceous, I would have probably classified birds as a peculiar,
but major, Order of Class Reptilia.  However, the end-Cretaceous extinction
killed off all the dinosaur intermediates, birds radiated enormously, so a
present-day classification justifiably recognizes them as a distinct Class
Aves."

Hence classifications are ad hoc inasmuch as they describe the broken
mirror. Nothing wrong, but that is what it is.

Richard Zander wrote:
"Say, if extinction is a part of speciation, then taxa are temporally
isolated. That is, every age has its own set of taxa, some the same as
other ages, some diffeent, some shifted or shifting their adaptive regimes
or stochastic trait allotments."

There is a circularity in this argument since geological ages have been
mostly defined by major changes in the taxa found in the strata. In any
case most taxa disappear not with a bang but with a whimper. Unseen and
unknown.

"Thus, one should not compare taxa adapted to environment a and c, with
similar taxa adapted to environments b and d in a different age. (Probably
some better way of saying this.)"

Classifications have a use-by date. Agreed.

"Lumping taxa because one finds an intermediate in bygone eras seems
nonsensical if extinction of intermediates is part of evolution."

But our present efforts to make trees of everything are pursuing this
ultimate fate. Maybe we could call it the blob classification. If fossils
didn´t exist (a foolish statement but bear with me) then we wouldn´t have
the current problem of fitting ever expanding grades into existing
classifications. Ultimately you run out of synapomorphies and end up with a
biodiversity balloon (theoretically and probably only ever attainable for
select groups, insects need not apply).

Jason


On 10 September 2013 23:41, Curtis Clark <lists at curtisclark.org> wrote:

> On 2013-09-10 12:02 AM, JF Mate wrote:
> > If we had access to fossils for every species that has ever lived our
> > classifications would be one large list of species names. And if we had
> > access to fossils of all populations of every species that has ever lived
> > we probably wouldn´t have species either.
>
> In my view, this is specious (in the classical meaning of the word).
> This would leave us with a taxonomy defined by what we don't know, which
> would be travesty beyond measure.
>
> One point of grouping by synapomorphy is that one can have groups in the
> absence of gaps. And a purpose for studying speciation is to understand
> species as evolutionary units (my favorite definition of phylogeny is
> "genealogy of species").
>
> In general, transitional forms are statistically insignificant. Remember
> that punctuated equilibrium was the application of peripatric speciation
> to the fossil record, and it was an explanation for the paucity of
> transitional forms.
>
> --
> Curtis Clark        http://www.csupomona.edu/~jcclark
> Biological Sciences                   +1 909 869 4140
> Cal Poly Pomona, Pomona CA 91768
>
>
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