[Taxacom] Reproducibility of descriptive data
s.thorpe at auckland.ac.nz
Fri Sep 11 18:34:26 CDT 2009
[Richard Pyle wrote] If I understand you correctly, in the world of sexually reproducing organisms, you believe a "real" boundary exists between species-entities in nature (independent of whether or not we humans have figured out where those boundaries are), and those boundaries are fundamentally more definitive (Australia-like) than the boundaries between things we humans call "genera" (and other higher ranks of classification). I'm not exactly sure where you stand on the "realness" of the boundaries between subspecies and other lower-rank taxa, but I'll go out on a limb and assume you think those gaps/boundaries are also not as "real" as the ones between species. And further, you believe that the basis for this natural "species" boundary is somehow directly related to reproductive potential. Are these fair and accurate representations of your opinion on this matter?
[reply] yes, that's pretty fair and accurate! Three things in particular lead me to this view:
(1) anybody who tried to draw species boundaries in such a way as to include, say, both human and chimp (assuming, contra Grehan, that this is a monophyletic pair) is not just "a bit of a lumper", but just plain wrong! This has nothing to do with any anthropomorphic bias against being lumped with apes. It has to do with the fact that anybody who tried to draw species boundaries in this way simply does not understand what is meant by "species", and is in fact talking at cross purposes. But human and chimp could be put into the same genus, no problem (provided that the genus also includes Pongo if Grehan is correct). What explains this difference between allowed lumping at the genus level vs. incorrect lumping at the species level?
(2) at the other extreme, anybody who tried to define their species with flagrant disregard for sexual dimorphism (and/or developmental (or other) polymorphism) would be equally out of line! IF QUITE DIFFERENT MORPHOTYPES FREELY INTERBREED, THEN THEY ARE THE SAME SPECIES, PERIOD!
(3) at least in the area of taxonomic entomology that I am most familiar with, the universal (or near universal) practice is to recognise species primarily by genitalic differences. Is this just because entomologists have some sort of "phallic fixation"?! No, what they are doing is saying that sufficient differences in genital morphology strongly suggests reproductive isolation. Here is an illustrative quote from this recent publication: Holloway, B.A. 2007: Lucanidae (Insecta: Coleoptera). Fauna of New Zealand, (61)
p.101 'Because of their identical genitalia it is tantalising to wonder whether the two species could reproduce if they were put together, but until that has been shown to happen, it makes sense to have a concise scientific name for the Sisters Geodorcus, the most unusual-looking species in the genus'
This is typical of conventional thinking. The author is saying that they MIGHT NOT BE DIFFERENT SPECIES, despite external appearances, but that she is hypothesising that they are distinct (=reproductively isolated) for now, and the onus of proof is on those who might claim otherwise
Also, what sense can be made of "cryptic species" if they are not reproductively isolated from identical-looking sympatric species? A cryptic species might be the vector for a deadly disease, while other morphologically identical congeners are not. This makes NO SENSE unless the vector "breeds true", at least most of the time. You need to stop that very real entity (i.e., the vector species) from entering the country. There is no leeway for choosing a different taxon concept of the species!
From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Richard Pyle [deepreef at bishopmuseum.org]
Sent: Friday, 11 September 2009 9:13 p.m.
Subject: Re: [Taxacom] Reproducibility of descriptive data
DAMN! After writing the message below, I just now saw Michael Heads'
beautifully concise statement of basically the same thing (I should learn to
read my entire inbox before responding). Now the conundrum....should I just
delete this message, and thereby effectively waste the last 15 minutes of my
life? Or should I click "send"? Hmmm....decisions, decis... [oops!]
You seem to be heavily invested in the idea that "natural" boundaries exist
between what we should all (eventually) recognize as "species", and that
these boundaries are somehow more "real" (Sharp? Discernable? Objective?)
than boundaries between, say, genera, or between subspecies.
Let's explore this idea a bit. I'll leave the "asexual" issue to Paul,
Brian, and others, and I'll focus on the sexually-reproducing beasties (and
If I understand you correctly, in the world of sexually reproducing
organisms, you believe a "real" boundary exists between species-entities in
nature (independent of whether or not we humans have figured out where those
boundaries are), and those boundaries are fundamentally more definitive
(Australia-like) than the boundaries between things we humans call "genera"
(and other higher ranks of classification). I'm not exactly sure where you
stand on the "realness" of the boundaries between subspecies and other
lower-rank taxa, but I'll go out on a limb and assume you think those
gaps/boundaries are also not as "real" as the ones between species. And
further, you believe that the basis for this natural "species" boundary is
somehow directly related to reproductive potential. Are these fair and
accurate representations of your opinion on this matter?
The crux, then, for discovering/recognizing these boundaries seems to boil
down to something like the probability that two given organisms can produce
viable offspring. If the probability is very high, then we would say that
the two organisms are the same species. If the probability is very low,
then we would regard the two organisms as belonging to different species.
If we select our two organisms from what a population geneticist would
regard as the same population, then the probability of reproductive
compatibility is very high. On the other hand, if the two organisms were
selected from what most taxonomists would treat as different genera
(animals) or families (plants), then the probability of reproductive
compatibility is very low.
The problem is, there is a continuum of examples in nature between what we
would call "populations", and what we would call "genera"/"families". If
there was some fundamental "natural" process that delineated "these two
organisms are the same species" from "these two organisms belong to
different species", then we wouldn't expect a single continuum; we would
expect a bi-modal sort of pattern. In other words, we would expect a
continuum of examples between kin-groups on up through subspecies; then some
sort of demarcation or inflection or discontinuity at the species boundary;
then another continuum from species complexes on up to Kingdoms. The
existence of a demarcation/inflection/discontinuity along the spectrum of
possible scenarios between "same population" and "different genera/families"
would be your smoking gun for the "naturalness" or "reality" of the species
When I was a student, I used to believe that such natural boundaries
existed. But after a couple decades traveling the Pacific and seeing
variation in my group of interest (coral-reef fishes), I can't seem to find
it. All I see is many different examples that fall at all points along the
continuum. And that's among vertebrates -- which tend to "follow the rules"
more closely than other groups (such as -- Egad! -- plants).
I'm not the only one who has arrived at this same basic conclusion after
many years observing nature. I'll repeat the quote I sent you off-list a
few days ago, from that clever bloke Darwin:
"No one definition [of species] has as yet satisfied all naturalists; yet
every naturalist knows vaguely what he means when he speaks of a species."
[...] "Hence, in determining whether a form should be ranked as a species or
a variety, the opinion of naturalists having sound judgment and wide
experience seems the only guide to follow. We must, however, in many cases,
decide by a majority of naturalists, for few well-marked and well-known
varieties can be named which have not been ranked as species by at least
some competent judges."
In other words: A species is what a taxonomist says it is, and a good
species is what a community of taxonomists say it is. (As has been echoed on
this list by several different people on multiple occasions over the years).
Richard L. Pyle, PhD
Database Coordinator for Natural Sciences
and Associate Zoologist in Ichthyology
Department of Natural Sciences, Bishop Museum
1525 Bernice St., Honolulu, HI 96817
Ph: (808)848-4115, Fax: (808)847-8252
email: deepreef at bishopmuseum.org
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