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Date: Wed, 29 Aug 2001 16:48:52 -0500
From: "Jonathan R. Wagner" <jonathan.r.wagner@mail.utexas.edu>
To: "Alastair G. B. Simpson" <simpson@hades.biochem.dal.ca>
Cc: PhyloCode mailing list <phylocode@ouvaxa.cats.ohiou.edu>
Subject: Re: Apomorphy-based definitions
From: Alastair G. B. Simpson wrote (edited for length):
> To me a crucial difference between treating people as individuals [...]
and
> treating species as individuals [...] is that, in the former case, the
succession
> from one individual to the next is marked by an extreme bottleneck [...].
> This gives a very obvious place to mark the
> arising of a new individual that few reasonable people would dispute.
> In the latter case there is no a priori expectation that a species lineage
> changing anagenetically over time will be punctuated
> by such profound marking events: i.e. most of the time it will be much
> much harder to decide precisely when a new individual (ie. new
> 'species') has emerged.
Your point is well made. I believe that my failure to see it earlier
comes from differences in how we see species.
In one of the two initial papers on the lineage segment concept, de
Quieroz points out that anagenetically-produced sequential morphotypes may
not really be lineage segments, but rather stages in the development of a
single lineage segment. In other words, anagenesis may not produce true
species. Think of it another way: if species are self-defining individuals,
would a simultaneous shift in morphology across all populations of the
species (however likely that might be) be an "individuality-disrupting"
event, or merely a change in characteristics of an individual? To abuse the
organism analogy, is the passage from larva to adult considered a change in
individuality?
So, in viewing species as individuals (the premise of the approach I
took in the original posting), the problem you point out is indeed resolved,
because such "anagenetic events" do not produce new species. I realize this
is somewhat frustrating, as it effectively "defines the problem out of
existance." However, as you point out (below), our approach to clade
boundaries is intimately connected to our approach to species boundaries.
> So, If you tie the origin of a clade to the origin of a species (as you
> necessarily do when you treat a species as the 'individual', however
> identified, from which the clade arose),
I see your point (see above).
> At this point I start to flounder a bit because I dont know how people
> propose to actually identify species (within a 'species are lineage
> segments' or related model): I cant offhand think of a way of doing it
> without leaving wide uncertainty zones between species ('fuzz'), [...]
For the record, I am not aware of ANY modern method of identifying
species under ANY species concept or criterion which does not leave such
zones of uncertainty. Perhaps I am too rusty on the subject. :)
Thanks for the response!
Wagner
Jonathan R. Wagner
9617 Great Hills Trail #1414
Austin, TX 78759