Real taxa => Ranking

Richard Pyle deepreef at BISHOPMUSEUM.ORG
Tue Sep 28 10:37:28 CDT 2004

> I wonder if it is possible to differentiate between 'objective' and
> 'universal'.

By "objective", I mean that the criteria are intrinsic to the organism,
outside of taxonomic literature.  The real question is, do purely biological
criteria exist among populations of living things such that, with a 100%
perfect and complete knowledge of that biology and a 0% knowledge of
historical published literature or other taxonomic opinions, two equally
wise observers would arrive at the same conclusion about where to draw lines
between species for all living things on Earth?

If the scope of "all living things on Earth" spans throughout history, then
the answer to this question is clearly "No", because over historical time,
life on Earth has been a continuous series of information transmission

But what about for a given temporal snapshot of all living things on Earth?
Or what about for a given temporal snapshot of all living things within any
particular "Kingdom" (as they have been traditionally, albeit subjectively,

The question isn't about whether we currently have the
technological/intellectual capability of doing making such objective
distinctions (i.e., it's assumed that we currently lack 100% perfect and
complete knowledge).  The question is about whether there is *any*
discernable (non-arbitrary) criterion intrinsic to the organisms themselves
that would indicate where any taxonomic line can be drawn?

Let's even drop "all living things" to a less stringent "most living things"
(say, more than about 80% of them).  And let's even allow for some arbitrary
threshold (e.g., % shared base pairs in particular genes).  Can we even
*then* imagine a set of objective criteria such that the process of drawing
species lines could be done with reliable accuracy, without the input of
subjective human judgment? (I use the word "imagine" to free us from the
binds of what we are currently capable of, both technologically and

> I would look at ranks as being objective in the sense that
> they can be referred to some kind of criterion that is open to
> independent evaluation (such as a geographic character, presence of a
> particular biological character) even though this criterion might be
> limited to that one taxon and a different criterion applied to another
> taxon so that the criteria are not universal.

Well, I suppose each individual taxonomist could declare some set of
criteria on a taxon-by-taxon basis, against which individual organisms could
be "tested".  But is there anything intrinsic to the organism (i.e., not
part of an arbitrary human definition) to say that one taxonomist's set of
criteria are objectively better than another taxonomist's set of criteria?

> In biogeography, taxa of different ranks have been utilized together to
> make biogeographic predictions about geology. Perhaps that means the
> different ranks held some kind of objectivity that connected them to the
> real world, or perhaps it just shows that it really does not matter.

My suspicion is the latter.


Richard L. Pyle, PhD
Ichthyology, Bishop Museum
1525 Bernice St., Honolulu, HI 96817
Ph: (808)848-4115, Fax: (808)847-8252
email: deepreef at

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