All species are transitional

Great stuff, Parasomnium.

What an odd comment.

That's what I was thinking too, and in that case your analogy about big and little numbers explains the arbitrariness very clearly.However, a popular definition now is "gene pool isolation," which I dislike because that makes the explanation that there are no "kinds" more difficult.When a gene pool gets isolated is not, I would think, an arbitrary designation. "Isolation" seems pretty definite to me.

Leaving aside for the moment sudden geographic isolation, what happens, I suppose, is that the genes that were once compatible become incompatible. But doesn't that mean there are noticeable physical differences that have already taken place?(obviously, I'm ignorant about this stuff).

What would be the cause of this change of behavior?

Brad, I hereby accuse you of pedantry.This message has been edited by robinrohan, 10-10-2005 09:16 PM

The most human-like response I've noted is the memorable phrase, "I don't chat."But that in itself hardly seems enough.

Some time ago I set myself the foolish task of going through one of Brad's lengthy posts and pouring over them until I understood the gist, after which I would submit a concise, pithy summary for the benefit of all.But it was too much for me; I gave up the project.I now realize that I had set myself a too ambitous task. What we should do is take a brief passage--say, one sentence--and study it together. For all we know, these outpourings may contain some profound statement about the meaning of life, about which I am rather anxious.So let's make a start. How about this: Any ideas what it might mean?This message has been edited by robinrohan, 10-12-2005 11:33 AM

Ben, that was brilliant. Just goes to show us that Brad is making sense in a sort of private langauge of his own.And apparently, we have inadvertently stumbled upon a basic McFallian dictum.

I understand that "moment of isolation" is not to be taken literally as a "moment," but how can we imagine a seamless gradual change from non-isolated to isolated? I can do that very well if we are defining "species" in terms of physical differences. If we define it that way, one can see how the designation that some such place along the evolutionary chain might be called a new species--but one might very well designate some other spot: that's what your analogy about big and little numbers indicates.This message has been edited by robinrohan, 10-19-2005 02:35 PM

The word "threshold" is troubling to me, but I'm not going to bug you about it anymore. Some kind of denseness on my part.ABE: maybe I'll start a new thread about my problem with defining a species as an "isolated gene pool."This message has been edited by robinrohan, 10-20-2005 03:17 PM

I have no problem with that. I understand it quite clearly; but that implies a different definition of "species" (physical differences).But if the definition is "isolated gene pool" then it does not seem like that is gradual. It seems like a "threshold." Either a gene pool is isolated from some other gene pool or it's not, I would think. In what sense does a gene pool become gradually isolated, meaning they no longer interbreed with a group they used to interbreed with? Does "gradual" mean on and off? Sometimes they interbreed and sometimes they don't until finally they stop altogether?

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

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.