[Taxacom] Reproducibility of descriptive data
s.thorpe at auckland.ac.nz
Thu Sep 10 20:10:14 CDT 2009
[Jim said] Your 'country' analogy is spurious. Like the US, Australia is an historical federation, defined by inclusion of various bits of land, including disjunct offshore islands and territories. That the bulk of Australia happens to coincide with recognizable continent is an irrelevant artefact. Notions of artificial or real in this context have no meaning.
[reply] You misrepresent my analogy. It is indeed intended to demonstrate a distinction between natural and artificial taxon boundaries, and I think that, properly understood, the analogy does just that. It is irrelevant how Australia is ACTUALLY defined, only that it could have been defined by natural boundaries as I suggest in the analogy. On the other hand, U.S.A. is not defined by natural boundaries. So, there is a difference between U.S.A. as actually defined, and Australia as it could have been defined. This difference is analogous to species (Australia) compared with genera (U.S.A.)
In other words, I am saying that when we talk about species, as opposed to genera, we are implicitly choosing to follow natural boundaries (which may not be 100% clear cut, but that is a different issue), and the notion of species in biology makes no sense if you disregard the biological species concept.
Consider this: males and females can sometimes be so dimorphic that they have little or no morphological similarity. But, NOBODY would consider them to be different species (if they realised that the differences were due to sexual dimorphism), not even people who would claim to be using a morphological species concept instead of a biological one! So, the biological species concept is firmly entrenched in our notion of species in biology, and it provides natural species boundaries (not necessarily 100% clear cut boundaries). This is completely lacking in the case of genera, families, etc. These supraspecific taxa are just "convenient monophyletic groups", but species are not...
MAIN CONCLUSION 1: There is a fundamental difference in kind between species boundaries on the one hand, and generic (or other) boundaries on the other hand, namely that species (and only species) follow natural boundaries (of reproductive isolating mechanisms). To ignore this fundamental difference is likely to lead one astray...
[Jim said] Descriptions do not 'define' a concept (at any level). They... um...describe it. If you want a definition, you could use the list of those thing you might include in that concept. Species in genera, specimens in species, etc.
[reply] Take the case of genera: a taxonomist who describes a new genus will include various species in it, say A, B, and C. These species must agree with the description of the genus, or else something has gone wrong! Now suppose another taxonomist discovers new species D, and places it in the above genus. You would have to say that the two taxonomists have different concepts of the genus, because the second one includes D, but the first guy/girl doesn't. Most taxonomists, I suggest, would say that the concept of the genus has changed only if the description needs rewriting to accommodate D. If D already fits the description perfectly well, then the concept of the genus remains the same. Hence, I suggest that descriptions do in fact define generic concepts!
In practice, taxon concepts for species are never "settled by inclusion"! If the describer of a new species has only a single specimen, that specimen does not fully represent the describer's concept of the new species! The describer will have some hypothetical notion of what it would take for another (non-identical looking) specimen to belong to the same species. Species descriptions based on a single specimen are not, I suggest, typically just descriptions of that single specimen! Instead, they EMPHASISE THE CHARACTERS OF THAT SPECIMEN WHICH THE DESCRIBER THINKS ARE LIKELY TO BE IMPORTANT! The describer's concept will either be confirmed or else falsified by other specimens as they turn up, depending upon WHERE THE NATURAL BOUNDARIES ACTUALLY LIE...
From: Jim Croft [jim.croft at gmail.com]
Sent: Friday, 11 September 2009 9:15 a.m.
To: Stephen Thorpe
Cc: Mike Dallwitz; TAXACOM
Subject: Re: [Taxacom] Reproducibility of descriptive data
Descriptions do not 'define' a concept (at any level). They... um...
If you want a definition, you could use the list of those thing you
might include in that concept. Species in genera, specimens in
Having settled on a concept by inclusion, you can then go about
describing it, listing the characters/attributes that, in your mind,
set the boundaries. It is conceivable that a taxonomist could account
for all relevant specimens, species, etc. This is, after all, why we
do revisions. Any character/attribute list is arbitrarily selected
and can never be complete.
Your 'country' analogy is spurious. Like the US, Australia is an
historical federation, defined by inclusion of various bits of land,
including disjunct offshore islands and territories. That the bulk of
Australia happens to coincide with recognizable continent is an
irrelevant artefact. Notions of artificial or real in this context
have no meaning.
On Thu, Sep 10, 2009 at 9:26 AM, Stephen Thorpe<s.thorpe at auckland.ac.nz> wrote:
> Jim, put another way:
> Genera are defined by descriptions (= genus boundary circumscriptions)
> Species are defined by nominating an individual as the type. Species descriptions (=species boundary circumscriptions) do not define the species. They can be incorrect descriptions of the true boundaries (unlike generic descriptions)
> Analogy: Australia can be defined by sticking a flag in the ground and saying "I hereby define Australia to be all the land in all directions from this flag to the sea". So, Australia is like a species (it has natural boundaries). U.S.A. is like a genus (it has artificial boundaries).
> Your "taxon concepts" are a mixture of two very different things: (1) generic descriptions; and (2) species descriptions.
> From: Jim Croft [jim.croft at gmail.com]
> Sent: Thursday, 10 September 2009 9:46 a.m.
> To: Stephen Thorpe
> Cc: Mike Dallwitz; TAXACOM
> Subject: Re: [Taxacom] Reproducibility of descriptive data
> Don't buy this. At all. And I do not think the codes do either. Nor
> many/most taxonomists. The type does not define the species (which
> are in nearly every case variable). It is an exemplar (not always
> 'typical' in the English sense) which anchors the name. The extreme
> example of this are species that have multiple synonymic types. In a
> type-defined species, concepts of lumping and splitting have no
> meaning - yet we all do it.
> Have a chat to Pete deVries. He would argue that a species knows what
> a species is and does not care what we call it or think it is. Humans
> develop a concept of what we think it is, sometimes (maybe even often)
> a reasonably good approximation of what a species knows it is. And we
> give a name to this human concept a name.
> There are three things: a species entity, a species concept and
> species name. The first is defined by biology and evolution, the
> second by humans, and the third is defined by the code and selected by
> The problem we have, and why taxacom exists at all, is someone utters
> the third, a listener assumes the first, without considering the
> second, of which there are often several alternatives.
> On Thu, Sep 10, 2009 at 7:03 AM, Stephen Thorpe<s.thorpe at auckland.ac.nz> wrote:
>> [Mike Dallwitz wrote] _Whatever_ we want to say about a taxon (e.g. what its boundaries, distribution, abundance, or uses are), we need to define the
>> taxon that we want to talk about. And the only way to do that is to describe it in a reproducible way, so that people can identify individuals as belonging or not belonging to the taxon
>> [reply] Species are defined by their name-bearing types (holotypes or lectotypes or neotypes or syntypes). A description of a species is a circumscription of its boundaries, according to the describer. So, we don't describe a taxon in order to define it so that we can then talk about boundaries. Rather, by describing it, we ARE talking about its boundaries, but the species is defined by its type.
>>>describe it in a reproducible way, so that people can identify individuals as belonging or not belonging to the taxon
>> No, describing it in a reproducible way only allows people to identify individuals as being within or else outside the boundaries of the species as circumscribed in the description. These boundaries could be wrong, so the description is certainly not a DEFINITION of the species (definitions are true by definition and cannot be wrong!)
>> What you say applies more to genera and other "subjective" taxa, but not to species, which are objectively defined once a type is designated...
> Jim Croft ~ jim.croft at gmail.com ~ +61-2-62509499 ~
> ... in pursuit of the meaning of leaf ...
> ... 'All is leaf' ('Alles ist Blatt') - Goethe
Jim Croft ~ jim.croft at gmail.com ~ +61-2-62509499 ~
... in pursuit of the meaning of leaf ...
... 'All is leaf' ('Alles ist Blatt') - Goethe
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