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

bti at dsmz.de bti at dsmz.de
Mon Sep 7 02:54:11 CDT 2009


 From
http://www.pnas.org/content/102/suppl.1/6600.full
Ernst Mayr and the modern concept of species
Kevin de Queiroz

"However, an examination of Mayr's writings on species reveals he had  
good reason for selecting this adjective. According to Mayr (42, 43),  
?This species concept is called biological not because it deals with  
biological taxa, but because the definition is biological. It utilizes  
criteria that are meaningless as far as the inanimate world is  
concerned.? The important idea for Mayr was that earlier concepts of  
species were based on properties, such as degree of difference, that  
could be applied just as easily to inanimate objects as to living  
things. Linnaeus (44), for example, recognized species not only of  
plants and animals but also of rocks and minerals. In contrast, a  
truly biological concept of species must be based on properties that  
are unique to biological systems, properties such as reproduction and  
interbreeding."

The problem that arises is that if a definition is attached to  
something that is not a universal feature then the definition should  
be re-defined to fit the biology of the organisms concerned. The  
simple dictionary definition of species is "a sort or kind". In  
sexually reproducing organisms one uses that biological feature to  
define that "sort or kind". I think it is well known that Simpson and  
Mayr had to juggle with how much interbreeding does one allow between  
species without calling into question that one has two species and not  
one.

Asexual "things" diverge and evolve as do sexual "things" the only  
major difference being that they don't need partners to do it.

Brian


Quoting Stephen Thorpe <s.thorpe at auckland.ac.nz>:

> 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
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