All species are transitional

Unfortunately, it is very messy and gene pools are not so isolated even when we call them different species.
See:
Message 132For a quote from Meyrs on this topic.

To me part of the problem is the concept itself. How isolated is isolated? Are we talking islands?Did you check the ring species article? Each variety occupies a distinct geological area and only overlap on the boundaries (and that is where hybreds occur). Are they isolated or just dispersed? When you get around to the end of the ring they behave as if isolated.Sometimes yes, it can be a distinct line: non-migratory birds on Hawaiian Islands are isolated from the mainland species they are (distantly) related to and always have been.Other times not so distinct. There are no clear "rules" here, because ultimately it is a totally artificial construction of human making.

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Now we are getting somewhere. They "partially interbreed."Let's say there's a group A which over time divides into Group B and Group C.According to this idea of partial interbreeding, we might have the following situation:Group A used to be an isolated gene pool.Now group B's members all can breed with each other. But some of these can interbreed with members of Group C--but not all. But all of them can breed with each other. So there are some differences within the ranks of group B. Some of them cannot breed with members of Group C. Time passes and generations pass and after awhile all the members of Group B are incapable of breeding with any members of Group C. So we have distinct species.What would cause these differences within the ranks of Group B?This message has been edited by robinrohan, 10-20-2005 11:45 PM

Robin,To illustrate what I mean, I've created this graphic for you. The transition "threshold" is the blurry light green area in the middle. As you can see, there is no clear boundary between the ancestor-wolf and the great dane, nor between the ancestor-wolf and the chihuahua, but there is a definite sharp boundary between the great dane and the chihuahua. {added by edit:}
The blurry beginning of the boundary between the dane and the chihuahua is meant to indicate that once mating between the ancestors of both was possible, but due to increasing difficulty became less and less frequent, until it became impossible altogether.I hope this helps.P.S. Criticisms of this picture are welcomed. This message has been edited by Parasomnium, 21-Oct-2005 01:04 PMEdited by Parasomnium, : updated image link

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"Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin.

This is indeed a very curious question. Curious in the sense that it beg's an answer. Para blue region still leaves the exact interpretation wide open.I will have to do some library hunting to collect all the materials I have seen that bear on this questioning but I'll try to describe some of this literature below.I saw in Wright's papers collected by Provine a curious diagram where isolation might be thought to occur by distinct branches. This was written in the period that Mayr was promoting allopatry. I have tried to read and reread the material from this time and I can only think that Mayr was unable to advance beyond use of the biological species concept BECAUSE of this diagram and his support therethrough of Wright on point over Fisher. The issue of what looks isolated will pretty much always look isolated from Fisher's perspective (Fords etc) but not necessarily from Wright's ("network") now thrown down other positions like Kimura's and Haldane's and Mayr simply renigs off the beans drunk in all the theorist coffee bags. Fisher sans (continentalism) asserts the need to show adaptive oversight. Waddington insists Bohr's Delbruckian bacteria are just as fit as a cheetah and Gould concluded they all hardened their nationalistic allegiances. Yet were is the question?The answer always comes in from out of the blue? The simple answer Para gave fails to notice that perhaps all these people were mistaken. Provine had insisted that Wright's idea of a shifting balance does not even begin to "work" because he conceived this motion to the peak, isolation threshold, or catastrophe set, or formerly discussed optimum fitness, was digramed EITHER as gene frequencies IN a population or gene combinations from a genome.Para's nationalistic doggodit physiognomical response is accurrate IF you do not think the analysis can be taken farther.********************************************************I, BSM, have tried to show that not only can the evolutionary synthesis be mild with respect to solids but that it can be analyzed in atomistic ways that can analyzed even with some chance dispersal by ways that the synthesists never geneticized. But it IS a hard thing to say that Aggasiz's fish diagram was still a dream but Croizat's is not.888888888888888888888
I don't know if this helps Robin. I should find the Wright picture where I thought he was expressing what must be an "isolated" gene pool. I hope it is not my memory that is at error this time.This message has been edited by Brad McFall, 10-21-2005 07:33 AMThis message has been edited by Brad McFall, 10-21-2005 07:35 AM

My critical comment is:It is a great representation.

Thanks, Ned. You had me worried there for a moment.This message has been edited by Parasomnium, 21-Oct-2005 02:39 PM

whew! You had me worried for a minute too. (as in what does para know???)

Your secret is safe with me, Ned. Just keep complimenting me.

Changing colors IS NOT FAIR, to posters who do not have your level of understanding. Need I point in ad nauseum that Wright USED (did not simply "paint") the color volume when working on the color inheritance in guinea pigs. Turning out pigs for creationists makes me blue and blurry. You are using speed to keep your point across and not necessarily solidity. Do you really think that money has an infinite circulatory velocity?This message has been edited by Brad McFall, 10-21-2005 10:30 AM

Thanks for sticking up for me, Brad. Quite right. It was very unfair of Parasomnium to start sticking colors and charts into his argument. I don't have any charts to fight back with. Me too. I can't think of a more unpleasant action than turning out a pig.This message has been edited by robinrohan, 10-21-2005 09:45 AM

Thanks a lot, Parasomnium. I got it now. I still don't like that particular definition of "species," but at least I understand it.

A speciation event is what occurs when biologists adopt conventions that establish which organisms are part of the new species.Okay, that's said partly as a joke. But there is some truth to it.Now consider the situation where a small group becomes isolated from the main population, and then undergoes change while still a small group. Suppose that this happened in the past when there were no biologists around to decide what was a species. And suppose that the small evolving group left no fossils, so that no new species could be established on the basis of fossil evidence. However, at a later time a successor group expanded its ecological niche and a large population developed, finally leaving evidence for that later group.How many intermediate species were there between the original species and the successor species? Remember that none of the intermediate organisms were observed.This type of situation is the one that has confused randman in where was the transition within fossil record?? [Stalled: randman].

Now I'm intrigued. Can you explain why you don't like it?

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"We are all atheists about most of the gods that humanity has ever believed in. Some of us just go one god further." - Richard Dawkins

I assure you, my level of understanding is quite average, really. I just thought that a picture might convey better what I meant. You know, as in the old adage "a picture says more than a thousand words". And what better way than using colours for depicting a gradual change? Why are you unhappy with the colours? As usual, I don't follow this, perhaps because you left out a few dozen steps of your thought process. But I am very interested in what you mean by that last sentence: "You are using speed to keep your point across and not necessarily solidity." Can you please explain this to me? I haven't the foggiest. But let's find out. Why don't you send me some?

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"We are all atheists about most of the gods that humanity has ever believed in. Some of us just go one god further." - Richard Dawkins