Sorry I accidently just replied to this while thinking about another e-mail
At 03:36 AM 7/8/2004, you wrote:
>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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