[Taxacom] FW: The 'reality' of species boundaries -- Once Again (UGHHH!)

[John Grehan]

It would be ironic if the EOL director did indeed have a proper
undestanding of the concept when Thorpe thought otherwise.

John Grehan
 

> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Stephen Thorpe
> Sent: Sunday, September 13, 2009 7:27 PM
> To: Edwards, James; taxacom at mailman.nhm.ku.edu
> Subject: Re: [Taxacom] FW: The 'reality' of species boundaries -- Once
> Again (UGHHH!)
> 
> Jim,
> 
> At the risk of being accused of further "ad hominem" attacks against
you,
> I simply don't think that you have a proper understanding of the
> Biological Species Concept! This is somewhat ironic for the executive
> director of EoL, don't you think?! :)
> 
> The Biological Species Concept (BSC) says that, for sexually
reproducing
> organisms, species boundaries (between populations) are defined by
high
> levels of reproductive incompatibility.
> 
> By contrast, a morphological species concept (MSC) would say that
species
> boundaries are defined by high levels of morphological dissimilarity.
> 
> Note that high levels of morphological dissimilarity, particularly of
> genitalia, are EVIDENCE for, but not DEFINITIVE of species boundaries
> according to BSC. Similarly, high levels of GENETIC dissimilarity are
also
> evidence of species boundaries according to BSC. Only high levels of
> reproductive incompatibility are DEFINITIVE of species boundaries
> according to BSC.
> 
> Now, you claim that the only significance of morphological
dissimilarity
> of genitalia, is that it may provide a "good character" on which to
base
> species distinctions, but that any morphological dissimilarity in any
> other body part might be equally "good"
> 
> 
> In cases where there is a high level of morphological dissimilarity in
> genitalia, the BSC and the MSC both give the same answer (distinct
> species), all other things being equal*. Not so when there is near
> identity of genitalia, but high levels of morphological dissimilarity
in
> other body parts. The MSC has no choice under such circumstances but
to
> give these other dissimilarities equal weight to genitalic ones, and
> thereby deem the species to be distinct on grounds of high levels of
> morphological dissimilarity! The BSC can go either way, depending on
> additional evidence for the level of reproductive incompatibility.
> Perhaps, there is no reproductive incompatibility between two given
> allopatric populations with high levels of (non-genitalic)
morphological
> dissimilarity! If so, the BSC says they are the same species, but the
MSC
> says that they are distinct species! My understanding of species in
> biology allows for the possibility of two allopatric populations of
the
> SAME SPECIE
>  S to diverge morphologically to a high degree in genitalic and/or
non-
> genitalic characters. The MSC does not. This is, in fact, the very
reason
> why, as YOU SAY, differences in genitalia don't prove reproductive
> isolation. This isn't a weakness of BSC, but rather its strength!
Using
> BSC, high levels of morphological dissimilarity (in genitalia or
other)
> can be overthrown by facts about reproductive compatibility, but not
so
> for MSC, according to which the morphological facts are DEFINITIVE of
> species boundaries!
> *Again, BSC is sensitive to other (non-morphological) evidence for the
> species not being distinct, after all. MSC is not, because the
> morphological evidence is DEFINITIVE! Again, my understanding of
species
> in biology allows for the possibility of two allopatric populations of
the
> SAME SPECIES to diverge morphologically to a high degree in genitalic
(and
> other) characters, if there is other (non-morphological) evidence for
> reproductive compatibility.
> 
> 4 quick examples:
> 
> (1) Michael Heads' duck: there is a highish level of non-genitalic
> morphological dissimilarity between mallards and grey ducks -
sufficiently
> high that we are pretty confident that they are distinct species, and
high
> enough for the MSC to deem them to be distinct. Does the BSC force us
to
> say that they are the same species, just because the grey duck is
being
> hybridised out of existence by the mallard? Answer: no! It looks like
it
> does, but only if you make the mistake of taking the fact that the
grey
> duck is being hybridised out of existence by the mallard to indicate
very
> low levels (zero, in fact) of reproductive incompatibility. In fact,
we
> haven't a clue from the example what the levels of reproductive
> incompatibility are, except that they are not 100% What matters is
> something like the proportion of mating events that lead to fertile
> offspring, and this could be very low (=very high levels of
reproductive
> incompatibility), for all we know!
> 
> (2) Richard Pyle's Centropyge: some details are unclear, but the jist
> seems to be that there are high enough levels of (non-genitalic)
> morphological dissimilarity between largely allopatric populations to
make
> most taxonomists consider them to be distinct species, but a
significant
> amount of hybridisation in a small overlap zone - enough hybridisation
to
> seemingly force the BSC to declare same species. In this case, it
appears,
> the BSC fails precisely because of its sensitivity to
non-morphological
> data! So, I need to show that either BSC can allow distinct species
here,
> or else that it is just plain wrong to think that they are distinct. I
> think the first option is best. One possibility is that we really
don't
> know what the levels of reproductive incompatibility are, as with the
> duck. The proportion of hybrids is just as much a function of time and
> other factors as it is a function of reproductive incompatibility.
> 
> (3) Beverley Holloway's (2007) description of Geodorcus sororum as a
new
> species distinct from G. capito: The Geodorcus on the tiny Sisters
Islands
> in the Chathams are the most distinctive looking in the whole genus,
and
> very different looking to G. capito in the rest of the Chathams. There
is
> huge non-genitalic morphological dissimilarity, but no genitalic
> morphological dissimilarity, and apparently even no significant
genetic
> dissimilarity! She justifies her erection of the new species on BSC
> grounds. Clearly, on the face of it, it seems to contradict BSC and
> require MSC. Her logic is that a non-genitalic morphological
dissimilarity
> of such immense magnitude is in itself strong prima facie evidence for
> there being high levels of reproductive incompatibility, even though
the
> "usual" evidence (genitalia, genes) is lacking. She considers that the
> onus of proof lies with anybody who disagrees with her to come up with
> convincing positive evidence of reproductive compatibility.
> 
> (4) cryptic species: these have identical morphology, but high levels
of
> genetic dissimilarity, interpreted as strong evidence for high levels
of
> reproductive incompatibility. Hence, cryptic species are consistent
with
> BSC, but not with MSC.
> 
> Cheers,
> 
> Stephen
> 
> ________________________________________
> From: Edwards, James [EDWARDSJL at si.edu]
> Sent: Monday, 14 September 2009 5:52 a.m.
> To: Stephen Thorpe; taxacom at mailman.nhm.ku.edu
> Subject: RE: [Taxacom] FW: The 'reality' of species boundaries -- Once
> Again (UGHHH!)
> 
> Stephen -
> 
> Ad hominem attacks are not the best way to get your points across. In
my
> "not perfectly logical (=rational)" way, I'll respond to a couple of
your
> contentions.
> 
> >The biological species concept is a great theoretical construct, but
it
> has very little relevance, I believe, to what taxonomists do in their
day-
> to-day work
> (You replied) I disagree! There are countless examples like the one I
> previously gave from Holloway (2007), suggesting that the true species
> boundaries are determined by facts of reproductive integrity, and
> justifying postulated boundaries in terms of the BSC. I suggest that
if it
> is not made as explicit as in this example, it is implicit in what
> taxonomists do in their day-to-day work, and if they are not doing
that,
> then I'm not sure what they are doing!
> 
> Edwards' comment:  The taxonomists I know are focused on identifying
good
> characters for distinguishing species. If they invoke the Biological
> Species Concept, it is after the fact.
> 
> >we taxonomists are agonizing over where we think species-level
> differences fall within the diversity we see
> (You replied) this statement is devoid of any meaning!
> 
> Edwards' comment:  This statement was in response to your contention
that
> taxonomists "agonise over evidence for or against reproductive
isolation".
> As I have said before, in my opinion taxonomists agonize over where
> species boundaries lie. We use characters that "work", and do not
> necessarily infer a direct connection between them and reproductive
> isolation. Sure, insect genitalia appear to be good characters that
*may
> (or may not) be* good species-level characters. That's why
taxonomists,
> even those who do not invoke the BSC, use them. So what? We also use
wing
> venation and a host of other characters, too, without making any
explicit
> reference to the BSC. The BSC is invoked after the fact, in an attempt
to
> explain the character distribution we have already inferred from the
> specimens examined, i.e. after we have already agonized over where the
> species boundaries lie.
> 
>             --  Jim
> 
> Dr. James L. Edwards
> Executive Director
> Encyclopedia of Life
> National Museum of Natural History
> Smithsonian Institution
> P.O. Box 37012, MRC 106
> Washington, DC 20013-7012
> 
> Phone:  1 202 633 8730
> Mobile:  1 571 230 4098
> Fax:      1 202 633 8742
> Email:   edwardsjl at si.edu
> 
> -----Original Message-----
> From: Stephen Thorpe [mailto:s.thorpe at auckland.ac.nz]
> Sent: Saturday, September 12, 2009 9:24 PM
> To: Edwards, James; taxacom at mailman.nhm.ku.edu
> Subject: RE: [Taxacom] FW: The 'reality' of species boundaries -- Once
> Again (UGHHH!)
> 
> Hi Jim,
> 
> I fully agree with your premises, but fully disgree with the
conclusions
> that you draw from them! Dare I suggest that you are not a perfectly
> logical (=rational) being? Well, nobody is, of course, but the "real"
> measure of a "man's" (=human's) rationality is how willingly they
engage
> in rational debate, so you can still "redeem yourself" by reading,
> thinking about, and then replying to what I am about to say! Sorry,
I'm in
> a slightly facetious mood! :)
> 
> > differing genitalia per se are not proof of reproductive isolation.
You
> are *inferring* such isolation
> I couldn't have said it better myself! Yes! Absolutely! You have
stated MY
> position with the utmost (almost) clarity! Differing genitalia per se
are
> EVIDENCE for reproductive isolation. Reproductive isolation is a real
> thing in the world (given a chosen threshold - see the analogy with
> statistics?) that we pay attention to when we do SPECIES LEVEL
taxonomy.
> Not so for genera, etc.
> 
> >But until you have done the experiments to show that hybridization
does
> not occur between two groups of organisms with different genitalia,
you
> have not discovered any boundaries due to reproductive isolation
> This statement is all over the place! My view is that we don't know
WITH
> CERTAINTY where the species boundaries are, but we accumulate
EVIDENCE,
> such as very different genital morphology!
> 
> >, you have used the morphological species concept to say that you
think
> that these morphological differences are so great that you believe
that
> the species could not/do not interbreed
> No, if you were to use a MSC (as opposed to BSC!), then morphological
> differences in genitalia would be no more or less significant than
> differences in colour or any other morphological character. So,
ceteris
> paribus,  two individuals differing hugely in colour but with
identical
> genitalia would be no less distinct species than two of identical
colour
> but with hugely different genitalia!
> 
> >The biological species concept is a great theoretical construct, but
it
> has very little relevance, I believe, to what taxonomists do in their
day-
> to-day work
> I disagree! There are countless examples like the one I previously
gave
> from Holloway (2007), suggesting that the true species boundaries are
> determined by facts of reproductive integrity, and justifying
postulated
> boundaries in terms of the BSC. I suggest that if it is not made as
> explicit as in this example, it is implicit in what taxonomists do in
> their day-to-day work, and if they are not doing that, then I'm not
sure
> what they are doing!
> 
> >we taxonomists are agonizing over where we think species-level
> differences fall within the diversity we see
> this statement is devoid of any meaning!
> 
> >However, until and unless we have done hybridization experiments, we
> cannot truly assert whether or how reproductive isolation might be
> involved in these differences
> it is unclear what you mean here: note that a MSC taxonomist has no
reason
> to do hybridization experiments - it would be irrelevant! If you are
just
> saying that hybridization experiments are stronger evidence for
> reproductive integrity than genitalic differences, then I can agree
with
> that, no problem!
> 
> Cheers,
> 
> Stephen
> 
> ________________________________________
> From: Edwards, James [EDWARDSJL at si.edu]
> Sent: Sunday, 13 September 2009 4:53 a.m.
> To: Stephen Thorpe; taxacom at mailman.nhm.ku.edu
> Subject: RE: [Taxacom] FW: The 'reality' of species boundaries -- Once
> Again (UGHHH!)
> 
> But differing genitalia per se are not proof of reproductive
isolation.
> You are *inferring* such isolation. Because genitalia are so closely
> involved with reproduction, you and most other insect taxonomists
believe
> that they are good indicators of species boundaries. But until you
have
> done the experiments to show that hybridization does not occur between
two
> groups of organisms with different genitalia, you have not discovered
any
> boundaries due to reproductive isolation. You have inferred that these
> boundaries exist, but you have not really shown that reproductive
> isolation is the cause. Instead, you have used the morphological
species
> concept to say that you think that these morphological differences are
so
> great that you believe that the species could not/do not interbreed. I
do
> not find that any more "real" or non-subjective than Rich Pyle
apparently
> does.
> 
> The biological species concept is a great theoretical construct, but
it
> has very little relevance, I believe, to what taxonomists do in their
day-
> to-day work. I know of very few taxonomists who "agonise over evidence
for
> or against reproductive isolation". Rather, we taxonomists are
agonizing
> over where we think species-level differences fall within the
diversity we
> see. Some of us then use the BSC to justify those decisions that we
have
> made on morphological or genetic or other grounds. However, until and
> unless we have done hybridization experiments, we cannot truly assert
> whether or how reproductive isolation might be involved in these
> differences.
> 
>             --  Jim
> 
> Dr. James L. Edwards
> Executive Director
> Encyclopedia of Life
> National Museum of Natural History
> Smithsonian Institution
> P.O. Box 37012, MRC 106
> Washington, DC 20013-7012
> 
> Phone:  1 202 633 8730
> Mobile:  1 571 230 4098
> Fax:      1 202 633 8742
> Email:   edwardsjl at si.edu
> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Stephen Thorpe
> Sent: Saturday, September 12, 2009 3:27 AM
> To: taxacom at mailman.nhm.ku.edu
> Subject: [Taxacom] FW: The 'reality' of species boundaries -- Once
Again
> (UGHHH!)
> 
> FYI: outcome of debate - stalemate! (see below)
> I do think though that Richard's view fails to make sense of what a
lot of
> taxonomists are doing when they agonise over evidence for or against
> reproductive isolation. Why bother dissecting genitalia?
> ________________________________________
> From: Richard Pyle [deepreef at bishopmuseum.org]
> Sent: Saturday, 12 September 2009 7:07 p.m.
> To: Stephen Thorpe
> Subject: RE: [Taxacom] The 'reality' of species boundaries -- Once
Again
> (UGHHH!)
> 
> Thank you for that.  I now feel I understand where you are coming from
on
> this (much better than before), and that we are at the point where we
> simply
> must agree to disagree.  In your world view, based on your experience
with
> nature, you have confidence that there are natural barriers between
> species
> groups.  My world view, based on my experience with nature, leads me
to a
> different conclusion.  Neither of us can be "proven" right or wrong --
we
> just have different perceptions of the natural world.  I doubt that
> anything
> else I say would change your mind, and I doubt that anything else you
say
> would change my mind. Not because we are both stubborn, but because
we've
> thoroughly explained our respective positions to each other, and we
seem
> to
> both understand where each other is coming from, but we've both failed
to
> provide sufficient evidence to compel the other to change their
world-view
> on this issue.
> 
> I can think of worse outcomes than that!
> 
> Thanks for the exchange.
> 
> Aloha,
> Rich
> 
> > -----Original Message-----
> > From: Stephen Thorpe [mailto:s.thorpe at auckland.ac.nz]
> > Sent: Friday, September 11, 2009 7:19 PM
> > To: Richard Pyle
> > Cc: taxacom at mailman.nhm.ku.edu; Gurcharan Singh
> > Subject: RE: [Taxacom] The 'reality' of species boundaries --
> > Once Again (UGHHH!)
> >
> > Richard,
> > >Where is the analogy in that?
> > I may have misinterpreted you, but you seemed to be
> > suggesting that because we need to choose a threshold of
> > reproductive isolation (90%, 95%, etc.) from a continuum of
> > possibilities, in order to define species boundaries
> > according to the BSC,  the species boundaries themselves were
> > therefore purely subjective. The analogy was that you do in
> > fact have to choose a significance level for a statistical
> > test from a continuum of possibilities, but the test itself
> > is not thereby rendered purely subjective.
> >
> > >just explain to me how we determine if there is sufficient
> > >hybridization (with as much implied fuzziness and imprecision as
you
> > >feel necessary) to decide whether we are seeing two separate
species
> > >with rare hybridization, or one single species with
> > imperfect gene flow
> > OK, I will: here we go: choose whatever threshold you like
> > (!), but better make it consistent with uncontroversial
> > cases. Having chosen it, the species boundaries are now
> > determined by the world, not by us! We must now look to the
> > world to see what they are. We look for evidence of
> > mechanisms that would result in X % reproductive isolation.
> > If we had chosen differently, then the species boundaries
> > would be different in some cases, but probably very few, as
> > most cases probably have virtually 100% reproductive
> > isolation, which is why chimp and human aren't the same
> > species by any "definition". So there is some leeway, but not
> > much. This is how it is done IN THEORY. IN PRACTICE, we don't
> > decide on a precise threshold and take it from there.
> > Instead, we look for evidence of "very high" levels of
> > reproductive isolation, such as very different genitalic
> > morphology, etc. What is "very high"? That is fuzzy.
> > Nevertheless, we look to the objective world to discover
> > species boundaries in a manner that is totally lacking for
> > genera or other levels. Species are more like Australia, ...
> > Genera are just "convenient monophyletic groups", unless you
> > believe in some sort of well-defined objective notion of
> > "overall similarity", in which case a particular threshold
> > could be chosen and then the genera would also be determined
> > by the world. I don't ...
> >
> > >> but the very practice of biological taxonomy for sexually
> > reproducing organisms involves trying to discover the natural
> > boundaries of reproductive integrity and calling them species.
> > >Yes, I know this is how you see it.  But I, and many other
> > taxonomists,
> > >see it a different way
> > I believe that I have just explained in what sense 'the very
> > practice of biological taxonomy for sexually reproducing
> > organisms involves trying to discover the natural boundaries
> > of reproductive integrity and calling them species'  is
> > consistent with your question 'just explain to me how we
> > determine if there is sufficient hybridization (with as much
> > implied fuzziness and imprecision as you feel necessary) to
> > decide whether we are seeing two separate species with rare
> > hybridization, or one single species with imperfect gene flow?'
> >
> > Regarding hybridisation, and with particular reference to the
> > most recent post by G. Singh, we must be careful to
> > distinguish the case where the hybrid population itself
> > becomes reproductively isolated from the parents, in a new
> > speciation event...
> >
> > Stephen
> >
> > ________________________________________
> > From: Richard Pyle [deepreef at bishopmuseum.org]
> > Sent: Saturday, 12 September 2009 4:32 p.m.
> > To: Stephen Thorpe
> > Subject: RE: [Taxacom] The 'reality' of species boundaries --
> > Once Again (UGHHH!)
> >
> > > >If that's your answer to the question, then why did you give
> > > me the bogus answer on statistics the first time around?
> > > Another "politician-like response" from Dr. Pyle! :) My
> > first answer
> > > was an analogy, and therefore not "bogus"!
> >
> > No, it was not an analogy.  Here is what you said:
> >
> > "so, statistics is all just human subjectivity, is it? Funny,
> > I thought the whole idea of statistics was to reveal
> > objective facts about the world! But wait ... how could I
> > have been so stupid? You have to choose a significance level!
> > So, statistics is all just human subjectivity after all ..."
> >
> > Where is the analogy in that?  It's a bogus answer because
> > you are misdirecting (dodging) my specific question.  I asked
> > you what proportion of hybridization was acceptable in order
> > for there to still be a species boundary.  You replied with
> > the nonsense quoted above, which I *think* was an attempt to
> > (snidely) imply that I was saying statistics were subjective
> > (which clearly this is not what I was suggesting).  It seems
> > to me that you are the one acting more like a politician here.
> >
> > > The fact that there isn't a perfectly precise objective answer to
> > > "which level of significance should we use?" in statistics,
doesn't
> > > make statistics any the less objective. See the analogy?
> >
> > No, I don't see how this is an analogy.  I already addressed
> > the precision issue in my later response.  Don't give me a
> > precise answer, just explain to me how we determine if there
> > is sufficient hybridization (with as much implied fuzziness
> > and imprecision as you feel necessary) to decide whether we
> > are seeing two separate species with rare hybridization, or
> > one single species with imperfect gene flow.
> >
> > > >But...what if the hybrid populations continue to persist?
> > > >Are they a third species? Or no species at all?
> > > That wasn't your original question!
> >
> > Yes, it was!  I asked what would happen if the two allopatric
> > populations disappeared, and all that was left was the hybrid
> > populations:
> >
> > "Now, let's say that the broad allopatric populations all die
> > out, leaving only the hybrid populations, such that 100% of
> > individuals form hybrids.
> > Are they now suddenly the same species, simply because the
> > allopatric populations disappeared?"
> >
> > When I asked "Are they now suddenly the same species" -- the
> > "they" was referring to the remaining extant individuals in
> > the hybrid zone.  I'm sorry if this was not clear.
> >
> > > I'm not sure that there
> > > is an answer to that, other than just "they are hybrids of extinct
> > > species".  I would lean to the third species option, since
> > some of the
> > > species we recognise today could have been formed as hybrids with
> > > subsequent extinction of parents.
> >
> > OK, that's a fair answer.  I don't agree with it, but at
> > least it is an answer to my question.
> >
> > > Anyway, I think I understand you as arguing that there is a
> > complete
> > > (or nearly complete) spectrum of interbreeding in the world
> > today, so
> > > no non-arbitrary place to draw species boundaries.
> >
> > To be precise, I am saying there is a nearly complete
> > spectrum of *examples* of different levels of interbreeding
> > in the world at all times (not just today).
> >
> > > This seems to be based on your own first hand explorations in the
> > > field. Am I right?
> >
> > In part -- but just as much (if not more) from my
> > conversations with other taxonomists working with different
> > groups of organisms, who also have many years of experience
> > observing nature.
> >
> > > If so, I can do little
> > > more than say that my "experience in the field" screams just the
> > > opposite!
> >
> > Fair enough.  Perhaps it is simply a function of our
> > different experience.
> >
> > > I suspect that you have seen a few cases where things are less
than
> > > clear, and this leads you to make the assertion that there is a
> > > complete continuum!
> >
> > No, that's not my assertion.  My assertion is that if you
> > look across *all* groups of sexually-reproducing organisms,
> > you will find *many* examples that confound a simply BSC view
> > of the world.  If these examples were confined to just one
> > kind of organism (like fishes), or if they were extremely
> > rare in nature, I would be more confident that a natural
> > barrier exists for species.
> > But too many taxonomists in too many different groups have
> > conveyed to me too many examples of the sort I have provided
> > for you, that it seems to me that the "fuzziness" of your
> > "Australia" analogy is, on average, much broader than the
> > intertidal zone and a few islands here and there.  In that
> > context, your analogy of Australia would be more
> > representative of typical species if the intertidal zone were
> > hundreds of kilometers wide.
> >
> > > I
> > > claim that in something like 95+% cases of sexually reproducing
> > > organisms, the levels of interbreeding are well within the
> > bounds of
> > > what is allowable according to a proper understanding of the BSC.
> >
> > I'm assuming that you just made up the "95%" figure -- which
> > is fine; let's use it.  That means that 5% of cases rely on
> > subjective interpretation by a taxonomist.  I would say that
> > 1 in 20 species being ambiguous is a non-trivial proportion
> > of biodiversity.  But I think you're a bit over confident in
> > your estimation.  From a lumper's view of the world, 95% is
> > probably about right.  From a splitter's view of the world, I
> > bet it would be more like 60%.
> >
> > > That is why we see lions and
> > > tigers, and why ligers and tigons are rare curiosities.
> >
> > Yes, but across the spectrum of biodiversity, mammals are
> > more the exception than the rule.
> >
> > > It could
> > > have been different. Yes, there are a few problem cases, which you
> > > seem to see as negating the general rule,
> >
> > OK, so at least you concede that you're talking about a
> > "general rule" in nature -- and on this point we may actually
> > come close to agreement.
> >
> > > but the
> > > very practice of biological taxonomy for sexually reproducing
> > > organisms involves trying to discover the natural boundaries of
> > > reproductive integrity and calling them species.
> >
> > Yes, I know this is how you see it.  But I, and many other
> > taxonomists, see it a different way.  We see evolution as a
> > continuous process, starting some
> > 4 billion years ago and continuing through an utterly
> > unbroken sequence of reproductive events to the set of extant
> > biodiversity we see today.  We recognize that the process of
> > "speciation" (i.e., the process by which lineages of
> > organisms develop reproductive barriers) is highly imperfect,
> > and riddled with exceptions to any "rule" that biologists
> > have tried to invent.  We don't see the process of assigning
> > names to organisms as the discovery of real entities in
> > nature, but rather as a highly effective means of
> > communication.  In many cases (at least 60%, and perhaps as
> > much as 95%), there is very little dissention among
> > taxonomists about how best to label clusters of organisms as
> > "species".  In the remaining 5%-40% of cases, there is
> > disagreement about how best to label biodiversity.
> >
> > To be sure, some of this disagreement is due to imperfect
> > knowledge.  With perfect knowledge, the disagreements would
> > be reduced in number.  But even with perfect knowledge,
> > evolution is a continuous process in the sense that every
> > organism that has ever lived is connected by an unbroken
> > sequence of reproductive events.  If you draw a slice through
> > evolutionary history at one particular time (like now), then
> > that slice will intersect every single stage of the
> > evolutionary process.  Your perception is that the proportion
> > of cases in that slice that are ambiguous with respect to the
> > BSC is small (5% or less).  My perception -- and the
> > perception of others who have spent a long time studying the
> > taxonomy of different groups of organisms -- is that the
> > proportion is not so small.  This, I suspect, leads to our
> > different perceptions of the degree of "realness" of species.
> >
> > > Not so
> > > for genera, etc., which are just "convenient monophyletic groups".
> > > Interestingly, I don't see Centropyge as being a problem case:
from
> > > what you say, the levels of hybridisation are low, with nothing to
> > > indicate that the level would increase significantly UNDER PRESENT
> > > CONDITIONS. Little wonder then, that "everyone" considers
> > them to be
> > > distinct!
> >
> > If I had to guess, I would say that something on the order of
> > 10% or so of all (combined) individuals of both species are hybrids.
> >
> > Aloha,
> > Rich=
> 
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