[Taxacom] Clade age (was: Taxacom Digest)‏

Lynn Raw lynn at afriherp.org
Sat Nov 12 10:28:18 CST 2011


I think the mistake we make is that our evidence concerns a very thin slice of time, like embedding a tree in paraffin, cutiing a section and then trying to understand which sections of twigs belong together. We can only define species in the present, not the past or future. Are the introduced Passer domesticus of North America still part of the Eurasian Passer domesticus panmictic system? I would say not, but you might have other ideas. Hmmm, maybe I just coined a new definition of species <G>.

OK, you don't like definitions but without them others do not always know what you mean. Maybe it is time to forget the theory, stop spending time arguing about the unknowable and start taking a far more pragmatic approach of identifying our co-passengers on the planet.

Lynn

On 12 Nov 2011, at 15:53, John Grehan wrote:


-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Jason Mate
Sent: Saturday, November 12, 2011 5:41 AM

> This takes me to John. A species´s subdivision is a matter of curtailing gene flow. 

So individuals at the extreme geographic limits of a distribution cannot interbreed even though their intermediaries do.

> You see, presently most researchers accept vicariance as well as dispersal as well as 
> sympatric/parapatric/allopatric speciation. So in my closet there are many boxes and one 
> has a label and it says ´Vicariance´. I have it right next to ´Dispersal´.

Yes this is the standard Darwinian toolbox. But acceptance is less the issue than how one gets there.


> Finally I would point out that De Queiroz´s lineage-as-species definition has its own 
> inherent problems. At what level do we call a lineage a species? What level of branching
> can we assume to be part of the lineage´s own ´fuzziness´?  Species tend to behave more 
> like networks than lineages so I can only see it working on physically isolated groups. A
> population on a mountain top or an island may be its own lineage, isolated (in this case
> physically) from other lineages but can one be certain that it is sufficiently distinct?
> The addition of other data, such as synapomorphies (phylo concept) would certainly help,
> but are the differences significant? What can we call significant?. I think that they all
> fail because it is a gradual process, and only time/extinction makes the cuts.

They all 'fail' because they are attempts at defining species when they are really attempts to define species boundaries using criteria that cannot apply to all species. What they are really doing is identifying parameters that are spatiotemporal (and therefore biogeographic) by which a species entity is predicted for a given time and place. Species, like any other taxonomic level, can be diagnosed. But as for 'defining' one ends up just tying oneself in obscure metaphysical knots.

So in the 
> end if you feel comfortable that it works on your group then go for it.

Which is what any diagnostician would do - stating of course the parameters that they identify for that purpose.

John Grehan



		 	   		  
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