The improbability lies in acquiring all (or enough to be distinctly sexually selected for) the same phenotypes by whatever mutations caused them.
I really don't believe you have any way of calculating the probabilities for such an outcome. You don't know what the original range of variation was in the ancestral population, you don't know the current range of variation among the varying populations, you don't know what sort of genetics are involved in the control of the specific morphologies observed. A highly polygenic trait is going to have a much higher probability of being affected similarly by a large number of different mutations, in different genes, than a trait which is regulated by one specific gene.
Your estimates of probability seem to be based on your own 'best guess' in the absence of absolutely any knowledge of the actual system. How can you possibly claim to be able to usefully estimate probabilities for a system you have so little information about?
If beneficial divergent mutations had been selected, then the species would have diverged. Either agree with my logic or tell me that no beneficial divergent mutations occurred (or tell me they weren't selected for somehow).
I don't agree with your logic beause your logic is faulty. Beneficial mutations need not cause speciation, there is absolutely no reason why one of these seperate ecomorph populations couldn't be absolutely chock full of beneficial polymorphic mutations, or even entirely novel genes, which have been strongly selected but are lacking in the same ecomorph of a different lake and yet still be perfectly genetically compatible and a likely mating choice. In the first place beneficial mutations need not be related to morphology and in the second the morphology only imposes certain limits of constraint on the possible variations and we don't know how narrow these constraints are.
It would have been interesting to have seen whether the different ecomorphs showed a preference in a mating situation with choice between their own population and that of a similar ecomorph from a different lake. The fact that they are not divergent enough to be a positive barrier to reproduction does not mean that they are not divergent at all.
What I've been trying to say is that it seems highly unlikely that drift and directional selection would lead to 3 cases of nearly identical speciation in the first place as the authors claimed.
Well sure thats what you've been claiming, but the claim doesn't really seem to have anything backing it other than your opinion.
I'm talking about having the same beneficial mutations selected for previously to such a degree that it results in a nearly identical divergence into the same subspecies in all three cases.
Except these
aren't neccessarily the same beneficial mutations, they are simpply mutations leading to the same beneficial phenotpye.
I'm not making that argument either
Then why did you say that "ONLY the new traits of the Limnetic and Benthic in niche X can be considered to offer ANY selective advantage to the species to such a degree that natural selection will discard (by some as of yet untold mechanism) ANY OTHER divergent beneficial mutations, in favor of retaining these!"?
Maybe it was just badly written and what you meant was any other beneficial mutation that happened to address exacty the same environmental issue, I'm sure you have carefully calculated the probabilities of all of those as well.
The changes that have occurred (if parallel evolution caused it) are at least large scale enough to have been naturally selected for and distinct enough for the fish and the researchers to recognize clearly now.
Now this is just an odd argument. Even very small effects can be selected for by natural selection and the distinct phenotypes the fish and researchers recognise need not be based upon large scale changes genetically. A small genetic change can have a large phenotypic effect.
Assuming, for arguments sake, that it isn't absurd to claim the ability to compare all the relevant environmental variables that affect selection within a given niche
Are you suggesting that I am claiming to be able to do this or that I am claiming that natural selection can? In the first case you are clearly wrong, I have never claimed such a thing, and in the second it is in the very nature of natural selection to reflect all the envrionmental variables.
you now want to assume that these PRECISE phenotypes occurred without interference from other selectable divergent phenotypes and at a minimum of 3 times, to the same species in each case (Limnetics kept looking more like their distant Limnetic cousins even assuming the Benthics never changed)?? Even if you can claim that natural selection is selecting for precisely the same traits in each habitat, you also want to claim that random mutation is now ordered to not produce any beneficial mutations that would cause entirely different looking but well suited sticklebacks?
quote:and since the original populations can be expected to have had a reasonably similar stock of genetic variance to work on to begin with
So because they must have had the same gene pool at one time, this so limits the number of possible beneficial mutations... that they must all be the same to this degree now?
I've lumped thse two together because the second is key to the first. The
entire point of parallel evolution is that it is the result of the common ancestral gene pool limiting the possible pathways along which the populations evolve, absent that it is simply convergent evolution.
As to me wishing to claim that random mutation couldn't produce equally beneficial traits producing a radically different morphology, I just don't know what the various possible genetic pathways to a species well suited for a benthic or limnetic niche are and neither, I suspect, do you. As I pointed out before some systems are more amenable to change than others, specifically those that may be determined by many different genes. I would certainly think that something like a change in size or colour would be an easier evolutionary pathway than developing a whole novel organ. In terms of these restrictions it is once again the fact that these ecomorphs all derive from a common ancestral marine population the imposes some obvious common constraints on the direction of their evolution, at least in a time scale such as we are talking about.
So 10,000 years is now a "broad window" in evolutionary time? We've gone from millions of years to get from x to "good enough" to less than 10,000 years to get from x to the almighty ecomorph?
The 'almighty ecomorph' is your own delusionary concept. There is considerable evidence that pre-zygotic reproductive isolation can take only a few hundreds of years to evolve, in that context then yes 10,000 years is too broad a window for you to make sweeping statements about the identical timings of establishment and timetables of evolution which have lead to these 3 sets of limnetic and benthic populations.
In terms of the origins of phyla or the diversification of the primates it may not be broad, but in the context of incipient speciation of a population of fish it certainly is.
Why be so constrained?
Because there is a wealth of genetic evidence pointing to a common bilaterian ancestor.
TTFN,
WK
This message has been edited by Wounded King, 07-22-2005 06:30 AM
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