Re: Species [arbitrary to a degree]

[Randy King <randyk@ims.com>]

Your definition of species is dependent on what we know and is.  It bothers me 
that the definition could change over time,
either by discovery or by evolution. 

If you find two ends of a ring species, they are two species.  Then you find 
the intermediate ones and its one species again.
And if the intermediate ones die off, its two species again?

Looking at it through time, all life (at least since sexual differentiation) 
could be arguably the same species since any incremental
change going back to the first sexual difference would always be of a same 
species.  

At 01:33 PM 10/19/01, Ken Kinman wrote:

>    I do think of a ring species as a populations of genes.  In the case of 
> circumpolar gulls, their physical mobility would naturally make the mobility 
> of genes easier as well.
>    However, if you have a "ring species" of something like a gopher (or other 
> rodent that has a small individual home range), the mobility of genes can be 
> greatly impaired.  As long as some gene flow continues through the 
> intervening populations of the ring, I would still regard it as a single 
> species.
>     Once gene flow is completely impeded at some point within the ring, the 
> process of speciation tends to speed up considerably, but if there is a 
> potential for the "impedance" to reverse itself, there is always the 
> possibility for gene flow to resume.  This demonstrates how fuzzy species can 
> be at the edges (especially in the time dimension).  Whether a given 
> "impedance" will cause speciation is subject to vagaries of historical 
> contingencies if the situation might be reversed before it is too late.
>    Luckily only a small percentage of species will give us such problems at a 
> given time in evolutionary history (such as the present time), but they do 
> demonstrate one of the reasons why the species problem is so difficult and 
> controversial.   But the recognition of species solves more problems than it 
> causes, so I am definitely not in favor of adopting a more simplistic 
> phylogenetic species concept (and the thought of abandoning species 
> altogether is horrifying).
>            -------Ken Kinman
>********************************************
>>The circumpolar gulls are only a problem because of trying to use
>>'species' in a way that relates directly to morphology.  If you think of
>>them as a population of genes, you can recognize that the mobility of
>>the genes within the population is unimpaired for having directional
>>constraints.
>
>
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