Dear colleagues,

Species, most contemporary biologists would argue, are real entities.
 These are lineages formed by intertwinning ancestor-descendant
relationships, so they all consitute a single evolutionay unit that changes
through time.  We can see a species as a rope made of numerous fibers,
which at some points fuse and at others break apart, but making a firm
wire.

Such a rope can, of course, fray apart.  This happens, for example, when
something like the isthmus of Panama appears in between.  The question,
obviously, is when will the two resulting threads might become distinct
enough as to prevent interbreeding when someone builds a transoceanic
canal.  The answer, alas, is far from evident.

Sometimes telling species apart is easy, because of characteristic color or
sculpture patterns.  Often, malacologists need much experience to confront
a given family, because the traits are subtle, or variable, or even
overlapping.  We all know how futile it can be to follow an identification
key to shells, just because so much variation and traits ought to be taken
into account.  However, nobody ever said that species should be easy to
tell apart!

In taxonomic practice, all available evidence must be taken into account.
 And the more, the better --that is why we struggle with molecular
genetics, statistics, and so on.  The bottomline, I believe, is pretty much
what Mayr said: two populations living together in the very same spot and
habitat, but showing no intermediates or other signs of interbreeding.  A
situation like this one is what provides a yardstick for evaluating (i.e.,
making a scientific hypothesis) the rank (species vs. subspecies vs.
nothing) of related populations that are not living in that same spot.

For example, I had to wrestle with Moroccan melanopsids, a puzzle for
everyone.  However, luck stroke me when I found two sympatric populations,
differing in rather subtle shell features, but having small but clear-cut
genetic differences.  And no single hybrid around.  This was the yardstick
to disentangle the rather complex pattern of melanopsid evolution in the
rivers of North-west Africa.

In my own opinion, then, species are out there, and we keep trying to know
and celebrate the diversity of life.  Scientific research must be open, so
it is unavoidable, and desirable as well, that different experts will have
contrasting hypotheses that need to be tested by reality.  There will
always be difficult groups to look at, and that is what makes malacology
most interesting: you are doing hard science from the very onset, you can
always learn more, yet you are never enough of an expert.  Or so I feel.

Very best wishes,

Cristian R. Altaba

-----Mensaje original-----
De:     Eduard [SMTP:[log in to unmask]]
Enviado el:     jueves 8 de julio de2004 07:08
Para:   [log in to unmask]
Asunto: Re: Ernst Mayr

Dear Tom and all

Perhaps one possible way to move forward with species problems is to go
from
simple to more complicated: first agree on species definition from a
conchological point of view and after that to think about more complicated
biological aspects of the problem. In such a way we can at least gather
facts and understand better what we are talking about. I do not think that
number of species and subspecies "depends on your personal approach to
taxonomy and the purposes and methodologies of distinguishing between one
species and another." We need definitions of taxa, which are more or less
in
consensus and understandable to most of us.

Because many members of this forum are shell collectors, I suggest to this
List to start a discussion in order to work out at least  primitive
(conchological) species and subspecies definitions.

Eduard Heiman

----- Original Message -----
From: "Thomas E. Eichhorst" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, July 07, 2004 7:45 PM
Subject: Re: Ernst Mayr


> Thanks John, that was a great read!  Mayr's definition of species is one
of
> many useful concepts he originated.  "A species is a group of actually or
> potentially interbreeding natural populations reproductively isolated
from
> other such populations."   Of course, the kicker is that "reproductively
> isolated" part.  Thus the small green nerite, Smaragdia viridis, found in
> the Caribbean and the Mediterranean could be separated into two species
(of
> course the literature is still fighting over subspecies status).  The two
> populations are sufficiently visibly different to enable almost anyone to
> separate them and the populations are reproductively isolated.  They may
> have interbred at one time (maybe around the Miocene), but the veligers
are
> no longer able to make the transatlantic journey.  If one believes in
> natural selection and speciation, then these two populations have been on
> that track for quite some time.  The question is where/when do we draw
the
> line and say, "Okay, you are now two different species."
>
> Perhaps Mayr's greatest contribution is that he sees this "grayness" to
> biology and does not believe we can finitely quantify this science with
> numbers.  Thus statistical analysis and cladograms are eminently useful
> tools, but they are only tools, part of a larger equation that also
relies
> upon field and lab observation and research.  The numbers can "prove" a
> close relationship between a clam and an echinoderm - but our eyes and
> experience tell us this is patently ridiculous.  A cladogram does very
well
> at pointing out possible and probable ancestral relationships, but falls
> short when used for classification of living species - even though it so
> often looks like it does just that.  Similarly, a statistical analysis of
> dimension, tooth count, weight, etc. between shells is an useful tool as
> long as one never believes this is the final answer.  It can demonstrate
the
> bell curve of variation within a population but I believe will always
fall
> short of differentiating species.
>
> All of the above is a layman's opinion and I am in way over my head, but
> always enjoy a good argument.
>
> Tom Eichhorst in New Mexico, USA
>
> > -----Original Message-----
> > From: Conchologists of America List [mailto:[log in to unmask]]On
> > Behalf Of John Wolff
> > Sent: Wednesday, July 07, 2004 7:20 AM
> > To: [log in to unmask]
> > Subject: Ernst Mayr
> >
> >
> > July 5 was the 100th birthday of eminent biologist Ernst Mayr.
> > He made major contributions to the concept of species.
> > A summary of his accomplishments and an interview of this remarkable
> > scientist done 5 years ago is available at
> > http://www.skeptic.com/eskeptic07-05-04.html
> >
> > John
> >
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