An answer to paraphyly?

Thomas G. Lammers lammers at FMPPR.FMNH.ORG
Tue Jun 17 06:01:46 CDT 1997


At 02:55 PM 06-16-97, Tom DiBenedetto wrote:

>To claim that one
>contemporary species is the ancestor of another strikes me as *very*
>divorced from reality, or at least from the meaning of the word
>"ancestor".

I never understood how our predecessors years back could spend time arguing
about how many angels could dance on the head of a pin, but now I begin to
comprehend.

The contemporary species we see today is of course NOT the ancestor of the
insular isolate.  But the species it was in the past IS.   I think we agree
thus far.  Where I differ is that I look at the continuity between the
species-it-was-in-the-past and the contemporary mainland species and say,
"Not much difference.  This is all one species." (I think of species as
four-dimensional: they have DURATION.)    Strict cladistic thinking would
insist on two species, which seems unwise if we could not distinguish them.

I guess the problem is, as Harvey Ballard so eloquently pointed out, that it
is not species which are the units of evolution, but populations.  If we
modify the statement to say that no contemporary POPULATION is the ancestor
of another species, we have a statement that sounds even better to me.  The
ancestor of my insular example was a POPULATION that existed long ago.  In
my taxonomic judgment, that population is considered conspecific with
certain currently existing populations.  If that upsets you, I'm sorry.

I will never accept  that the evolution of a new species from an existing
one somehow magically transforms what is left into a new species itself, any
more than the simple death of individuals or extirpation of populations can
transform what remains  into a new species.  We can put forth all sorts of
wonderful theoretical arguments and philosophical convolutions, and redefine
terms until we're happy with the results, but in the end, it is just plain
silly.  The plants on the mainland are the exact same species, by any
reasonable standard, on the day AFTER the dispersal event occured as they
were on the day BEFORE it occurred.    For a real world example,
Stephanomeria exigua subsp. coronaria was no different on the day after
chromosomal rearrangements in one of its populations created sympatric
Stephanomeria malheurensis  than it was on the day before this event (cf.
Amer. J. Bot. 60: 545-553. 1973; 70: 276-284. 1983).  However we wish to
deal with it nomenclaturally and taxonomically, it is a fact that groups of
populations that meet various criteria of "species-hood" routinely emerge
out of the middle of other groups of populations that meet various criteria
of "species-hood", thus creating a pattern we dub paraphyly.  We cannot
legislate it away or define it away.  We must deal with it in a rational and
sensible fashion.



Thomas G. Lammers

Classification, Nomenclature, Phylogeny and Biogeography
of the Campanulaceae, s. lat.

Department of Botany
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, Illinois 60605-2496 USA

e-mail:     lammers at fmppr.fmnh.org
voice mail: 312-922-9410 ext. 317

*******************************************************************
"In no affairs of mere prejudice, pro or con, do we deduce
 inferences with entire certainty, even from the most simple
 data,"
                -- Edgar Allan Poe




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