[Taxacom] Reproducibility of descriptive data

[Stephen Thorpe]

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
humans.

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.

jim

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...
>
> Stephen
>
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