A clarification

[Stuart G. Poss]

Thomas G. Lammers wrote:
>
>
> A type specimen is merely a standard of reference to which a name is
> permanently attached.  It serves much the same function as the kilogram bar
> or liter volume at the Bureau of Standards.  Types permit us to answer the
> question, "Just what did that person have in mind when they described that
> species and validated its name?"

It has nothing to do with "biological
> reality", i.e., it is not necessarily "typical" in any statistical sense.

> In fact, it may be highly aberrant. The type of the grass Tridens flavus has
> yellow spikelets (hence the name) ... despite the fact that this is a rare
> mutant and 99.9% of all individuals have purple spikelets.

I must confess ignorance regarding the botanical codes.  However, in
Zoology it is not quite correct to say that the holotype serves much the
same function as a unit of measurement as defined by the Bureau of
Standards nor that it has "no basis in reality".

The holotype is as Thomas points out is a reference specimen.  He
further correctly points out that it need not be a "typical" specimen.
However, the fundamental point is that the name given to the holotype
must also be used to refer to all other members of that species
[subspecies], henceforth regarded as "the same" by competant taxonomic
experts.

Experts, need not agree on the concept of what that species [subspecies]
does include or does not include in terms of natural variation, but by
definition they agree that the name to be used for the species
represented by the holotype is the name associated with the type.  Use
of other names is forbidden, and the rules are quite specific in
establishing the priority of synonyms, names that refer to the SAME
species.

It should be noted that while a particular holotype need not be typical,
the law of large numbers states that on average, it will generally be
typical for most features.  However deviant in some attributes, it would
presumably have other attributes expected to be seen among other
representatives of the species, or would have had had not someone killed
it or only preserved a part of it.  Consequently it generally is, on
average, predictive of its representatives.

Clearly the state of preservation will determine what kinds of
observations and subsequent predictions can be drawn.  The holotype may
in some cases only be represented by what remains of the species, but in
principle, it is (hopefully) available for direct comparison.
Obviously, any species whose type specimen deviated in every feature
(not just those someone first observes) from other representatives of
the species, would useless as a holotype (reference specimen).  In all
probability, such a species would be described more than once, but by
fixing the name to be used to a specimen, this situtation would be
relatively rare.  In order to better assess natural variation, modern
taxonomists will often  designate paratypes, when material is available,
to faciliate the distinguish species (ie. assigning them to disjunct
set-thoretical classes that must bear a different name, if not a member
of the class that includes the holotype).

Since the concept of species (or subspecies, should the type be for a
named subspecies), is essentially a predictive concept, the taxonomy
used to establish the name is fundamental to other biological
observations, whether they be made with confocal microscopes, molecular
chemistry, or some other method of observation.  The name may prove the
single static attribute of such a dynamic yet, obviously highly
predictive concept of "species", but because it must be static by
definition it actually allows us to scientifically make statements about
species.

This notion of a reference system differs somewhat from reference
systems used in physical measurement, because natural variability in the
reference object is expected in biological systems.  Although holotypes
too can be measured with imprecision, experimental error is not regarded
as the sole source of variation, as is the case with physical standards.

--
Stuart G. Poss                       E-mail: sgposs at whale.st.usm.edu
Senior Research Scientist & Curator  Tel: (228)872-4238
Gulf Coast Research Laboratory       FAX: (228)872-4204
P.O. Box 7000                        703 East Beach Blvd.
Ocean Springs, MS  39566-7000