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Re: a point of view or what does it take to be...?


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Posted by paalexan on February 18, 2003 at 19:28:25:

In Reply to: a point of view or what does it take to be...? posted by Wulf on February 14, 2003 at 05:28:45:

:Hi folks,

:thanks to Linnaeus we today have a quite well organized system in systematics. But on the other hand there are some more or less uncertain definitions of what makes a genus, a species, a subspecies or only a race.

Since it seems from later posts in this thread that you might be hoping for opinions, here's mine: the definitions of `genus', `species', `subspecies', and `race' aren't uncertain, they're nonexistent. The `biological species concept', the most widely accepted definition of what a species is, and one often taught as `the' species definition in major textbooks (such as Campbell et al's `Biology') is simply inapplicable to many taxa (many ferns, for instance, and among herps, Cnemidophorus, Lacerta, and other genera with asexually-reproducing species) and which also faces a good bit of opposition on theoretical grounds from many taxonomists. OTOH, I don't think there's a better species concept waiting on the wings. And things aren't a lot better for genera and subspecies... a lot of taxonomists would like to see subspecies done away with entirely, and a genus is nothing more than a taxon more inclusive than species and less inclusive than `tribe' or `subfamily' (or whatever taxon level a given taxonomist chooses to recognize as being at the next level up from genus... another place where there isn't a solid consensus).

:As for the family of pythonidae i.e. Stimson & Underwood (1990) lumped together almost (except Aspidites) all indo-australian pythons into the genus Morelia but this genus already had a key as well as others genus did. Other taxonomists seperated them again and Kluge (1993) for instance ignored the validity of Liasis fuscus but placed him into Liasis mackloti as a race (if you have a closer look at these two you'll find out a lot of differences, including locality).
:
:So there were different points of view and I guess all of them somehow had their right.

So far as how inclusive a taxonomist wants a genus to be, that's simply a matter of personal discretion. So long as the genus is monophyletic (and some taxonomists wouldn't even require that) and doesn't either include larger taxa or become included in a smaller taxon, anything goes.

:But what makes specimen to a subspecies? Is it only a perhaps remote locality where it occurs or maybe a slightly different morphology (i.e. a second pair of parietals or a higher ventral or subcaudal scale count; +-2 or 3 scales) ?

In practice, a subspecies is simply any subset of a species that is reasonably distinct geographically and morphologically.

:What is a race worth in taxonomy and how would one describe it?

I hadn't thought races even had any taxonomic standing. It's just a word you use when you only want to talk about a subset of a species, but that subset doesn't have any formal designation.

:What is a key to a genus worth when specimen placed into this genus all show character sets that should be abesent in order to the key?

Here I'm just not sure how you're using `key'. The usage of `key' in reference to taxonomy with which I'm familiar is that a key is simply something used to identify a species... if a key that's supposed to allow you to identify the members of a genus doesn't allow you to identify a species that's been added to the genus, the key simply needs to be changed.

:Is an posterior parietal always a posterior parietal or could it be just a enlarged temporal scale?

I imagine you'd be more likely to be understood if you called it a posterior parietal...

:As WW already said..."Taxonomy is a matter of evidence...". But what is evident when things chance?

Evidence (data) is only half of taxonomy. The other half is people making subjective decisions about how the data should be interpreted, and how much data they need...

Patrick Alexander



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