[Taxacom] FW: Why Australians are more real than Americans: implications for taxonomy!

[Stephen Thorpe]

Just to preempt a rather obvious objection to what I said below, one might object that if ANY consistent morphological gap defines a species, then probably every INDIVIDUAL will end up being a different species! Two possible replies:

(1) We look for morphological gaps between POPULATIONS, not individuals! Only if there is a consistent morphological gap between every individual in one population compared with another are the two populations to be considered distinct species, no matter how small the gap. Problem: how do you define population? I think we end up at (2) below, whichever way we try to go:

(2) the biological species concept (i.e., reproductive isolation under natural conditions) is the only way to go, and cannot be avoided without ending up in contradiction! We can never be sure if two populations would maintain reproductive integrity, but science is all about making hypotheses based on evidence, and that is exactly what we must do! If the genitalia are quite different between populations, for example, then we hypothesise that this difference is sufficient to ensure reproductive isolation. And in fact a population itself is a "dispersively connected" bunch of individuals for which we hypothesise no barriers to reproduction.

So if one taxonomist says it is that species, and another says not, there will be a right answer depending on the presence/absence of reproductive barriers in the hypothetical event of the two populations "coming together" under natural conditions. We can never no FOR CERTAIN, but that is true of most things...

Not sure where this leaves asexual things...

Stephyen

________________________________
From: Stephen Thorpe
Sent: Monday, 7 September 2009 2:16 p.m.
To: Richard Pyle; TAXACOM at mailman.nhm.ku.edu
Subject: RE: Why Australians are more real than Americans: implications for taxonomy!

Richard,

I think the list can benefit from new angles on old and tired debates, so I am replying to the list, despite your advice that this will just bore people to death! :)

> There are gaps at all scales.  To say that species boundaries are "real" is to say that the gaps that cluster around at the species level are somehow special -- more real than the gaps at higher or lower levels

I agree! I wasn't trying to imply that species level boundaries are any more or less "real" than any other level can be, except that lumping/splitting of genera, say, is more subjective than lumping/splitting of species, at least if you follow a biological species concept. The whole Hominidae could just as correctly be a single genus, for example. Lumping/splitting species is a bigger can of worms.

I think I see where you are coming from: consider allopatric populations which differ only slightly (=very small gaps). Are they the same species? Well, there is a determinate answer (independent of us)  if you follow a biological species concept, it is just that the answer can perhaps only be guessed at, and never known for sure. The nitty gritty now becomes clear: if you follow a morphological species concept, then ought ANY consistent gaps be species distinctions, or is there room for subjective choice regarding how much of a gap is required?

Thought experiment: imagine that all the species out there look the same as they actually do, but they don't breed, they just exist! So, no chance of a biological species concept. Could we still do meaningful (descriptive) taxonomy? The same patterns of morphology and "gaps" would still be there to describe...

I'm now less certain of my views, but one thing strikes me: if we follow a morphological species concept, for it to make any coherent sense, we might have to consider ANY consistent morphological gap to be a species boundary! The only reason why we often do ignore such small differences between allopatric populations is that we consider the gaps to be insufficient to produce reproductive isolation...

The reason why all this is relevant at present, has to do with the correct understanding of "identification" (at least at the species level):
if you are right, then two identifiers can disagree PURELY subjectively about the identity of a specimen - one of them can be correct relative to his concept, and the other can also be correct relative to the other's own concept. There would be no "fact of the matter". In that case, an identification without specification of the relevant taxon concept would be fairly meaningless.

But, on my Australia analogy, to identify a specimen is to say that a given land coordinate is part of Australia (forgetting all the little inshore islands and Tasmania), and there is a fact of the matter about this.

So, it all seems to come down to which species concept is used/best/true. The subjective view on species identification presupposes a morphological species concept with subjective choice on how wide the gaps need to be. On either a biological species concept, or a "gap or no gap" morphological species concept, there is only a single true species identity for any given specimen...

Stephen