Re: Species [arbitrary to a degree]

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: "Ken Kinman" <kinman@hotmail.com>
Sent: Friday, October 19, 2001 4:04 AM


>      The continuity of life is a fact that cannot be escaped even at the
> species level (or at the population level for that matter).  Even species
> are somewhat arbitrary at some level, [...]
> It's a bit like the Heisenberg Uncertainty
> Principle of biology, and there is no getting away from it-----so we have
to
> accept it and do the best we can.

I agree with all that.

> It therefore seems a good time to end the fruitless struggle to
> totally eliminate [...] paraphyly from classifications, as it is a natural
> consequence of the continuity of evolution.  The total elimination of
formal
> paraphyletic groups from classifications is not only fruitless, but
> unnatural.

Of course I agree that _species_ must be paraphyletic and must have fuzzy
boundaries. But I don't think we need to carry on the paraphyly into "higher
taxa". The PhyloCode is surely not the first document that almost
desperately stresses that species and clades are totally different kinds of
things (just for the record, I agree that species should be imagined as
"lineage segments" that can sometimes have shapes like Y or more complicated
ones). It can even be argued that the boundaries of species and clades need
not coincide, so for example the first saurischian populations, the first
ornithischian populations, the MRCA of dinosaurs and its immediate ancestors
might belong to the same species (biospecies or morphospecies, probably also
ecospecies). (Of course this example is stupidly theoretical.)

The concept of lineage segments means that mere anagenesis can be used to
separate 2 (chrono)species. I _hope_ that punctuated equilibrium is common
enough to make this practical, because otherwise drawing lines is _100 %_
arbitrary. But, as HP Jaime A. Headden wrote, in most cases we don't have
anywhere near the data to even suspect anagenesis!

> Perhaps it is just better to admit ranks
> are all human constructs on some level,

and to live on with that, saying "I'm doing stupidities right now, and I
know it, but I don't care" all the time? :-S
        Contra Benton I really don't think we should count families or
genera when we want to know about biodiversity and should be counting
species. Of course we can never be sure that paleontological morphospecies
are real species, but counting them should still give much more useful
figures than counting ranked groups.

> and get on with the job of minimizing the arbitrariness at every rank
> as best we can.

I ask the simple question "how" and expect a long, complicated answer.
Please don't disappoint me :-)

> Arbitrariness can't be eliminated, and therein lies the
> blind side of strict cladism.

Not sure if you disagree with me; IMHO arbitrariness in assigning every
organism to a species can't be eliminated even in theory. Arbitrariness in
assigning every organism to clades is theoretically eliminated as soon as we
know its phylogenetic position (theoretically and not in practice _only_
because we can't know the phylogenetic position of everything).

BTW, can anyone think of a definition for subspecies? Geneticists seem to
use clades within species; is that generally a good idea?

> >On Thu, 18 Oct 2001, Graydon wrote:
> >
> > > A species is a population where there is no genetic restriction to the
> > > degree of the common descent among the next generation from any member
> > > of the species -- they can all mate effectively with each other, given
> > > the opportunity.

BTW, I don't understand this formulation, apparently my English stops here.
Can someone explain?

For not to begin many short posts, I write here that "cladogram" is entirely
Greek, not Latin (klados, gramma); that when a barrier appears in the middle
of the geographic range of a ring species (or series species which only
means that the ring hasn't closed), or "the intermediate ones die off",
sooner or later 2 totally separate species will evolve from it; that I'm
totally shocked about the sale of highly radioactive fossils and the
statement "A little radiation never hurt anybody", which has after all been
falsified much too often; that "restricting the species concept to
populations of genes" is impractical, maybe even more than the traditional
biospecies; and that species can differ very little genetically when
mutations that concern the sexual organs (or the times of breeding...) have
occurred.
        Just for the record (I apologize for any possible political
implications), while dog breeds are relatively distinct populations (by both
morphology and genetics), human """races""" are nothing of the sort. The
"""racial""" characteristics appear to be nothing more than _individual
variation_. The most isolated human population _ever_ (IIRC) were the
inhabitants of Easter Island for just a few hundred years, and nobody has
ever invented a separate """race""" for them. The rest of humanity is little
more than _one_ population, despite the rather weak connections between some
demes.

***************************************
We really look like one subspecies of chimpanzee that has gone out and taken
over the world.
        can't find the author at the moment, maybe Svante Pääbo, anyways in
Nature some months ago