All species are transitional

So what you are saying is that more mutations are not necessarily required? That's what I want to know.

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"Turning out pigs for creationists makes me blue and blurry."--Brad McFall

You're right. I misstated it.

Let's say this happened.We had semi-isolation, as you described, for a while, and then "final divergence" occurred. Could we pin that event down to a particular date? What does final divergence consist of? I guess we could say that when the last lightly speckled creature died, at that moment in time--100 hundred million years ago, give or take a few days--we suddenly had 2 distinct species--heavily speckled Eutherians and black, unspeckled Eutherians. That's according to the definition of "gene pool isolation."Seems like a quite definite moment in time to me.

When does bay become ocean? When do foothills become mountains? When does a boy become a man?As the genetic similarity between two populations declines from 100% to 99.9999% to 99.9998% and so forth, at what point should the two populations be deemed separate species?These are rhetorical questions. Any chosen dividing line is arbitrary.--Percy

The moment they are totally isolated. What's arbitrary about that?

The moment that they are "totally isolated" is completely arbitrary. That's what's arbitrary about it - it's arbitrariness.

In the contrived example we are discussing the isolation becomes complete when the mixed population dies away. So if you take this as the "speciation" you're saying that the heavy speckles are not a species at one moment and then when something over the nearby hill gets swallowed by a boa it suddenly becomes a species.That may be correct in some way, but it is a bit odd.

But can you guarantee that sexual isolation remains a dividing factor?Perhaps if a survival stress were applied to the area where the asian green warbler ring species overlaps that there would exist individuals that would interbreed even after having been sexually isolated.You could have transition back and forth.

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RebelAAmerican.Zen[Deist
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That's it exactly. While the lightly speckled Eutherian was still alive, there was the possibility of gene flow between the two other groups, since the lightly speckled one could mate with both groups, but the other two groups couldn't mate with each other, as you and RAZD explained. The moment that lightly speckled one died, there was total isolation.This is why I have a problem with that particular definition of "species"--it's not arbitrary, by which I mean it's not a matter of just labelling something a different species out of convenience.However, if we adopt another definition--physical changes--the labelling is arbitrary. The only difference between the 2 groups is that one is speckled and one isn't. Otherwise they are identical. One could call them variants using the other definition. But you can't do that with "gene pool isolation."This lack of arbitrariness matters if the various analogies about seemlessness are going to work (color spectrums, etc.)This message has been edited by robinrohan, 10-27-2005 07:02 PM

I'm not sure what you are referring to here.

The sexual selection barrier may apply when the living is easy, but when times get tough the selection of mates may be less picky when survival is at stake.This was observed on the Galapagos Islands when two finch species interbred during a drought that did not interbreed before or after the drought.Line ... no line ... line ...

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RebelAAmerican.Zen[Deist
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Any way to know why they didn't interbreed before that?

So the blocking mechanism preventing mating between different species, barring environmental factors, is tied in with physical appearance or a surface level. As against a block on the cell level where different species may mate but produce no viable issue?Wish I could explain that to my neighbour`s Dalmatian who repeatedly humps a concrete statue of Venus deMilo in his garden.

What you are seeing is (usually male) sexual behavior with object less and less similar to potential mates due to a lack of better opportunities. This is one of the driving forces for the trend to regress species diversity in times of survival stress.Or it is in love with an image of the master.

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RebelAAmerican.Zen[Deist
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General lack of opportunity coupled with plentiful normal opportunity would by my assumption. When species are in survival stress they tend to move outside native territories looking for ones more like what they knew before, and this puts them into a position of more interaction with other species. On the Galapagos we have descrete islands so it is easy to focus on when the barriers are crossed.

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we are limited in our ability to understand
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RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.