All species are transitional

What does this mean? We are trying to settle on a defintion of "species."--------------------------------------------------------------------------------

Ok, I understand. But there would come a point--would there not?--a quite definite day, when one had a new species (according to the definition). If one had a time machine, one could date it.

Let me go over this and see if I can clarify it in my own mind.Let me add a little to the scenario by saying that the speckled coat is important for survival, and the MORE HEAVILY SPECKLED it is the better. There are some big bad predators around, and the only way these little critters can defend themselves is by hiding. The heavy speckles allow them to blend visuallly into the bushes. They happen to be Eutherians--ancestors of me and my cat--and if this little group doesn't survive I and my cat won't ever exist. We need more speckles!The initial light speckles was created by a mutation.What I'm trying to figure out now is how the coat goes from slightly to heavily speckled. Surely there is not a series of mutations as regards just this one feature (the presence of speckles). That would seem very unlikely, unless I'm confused about the nature of mutations.I was thinking that when you got to the point, after some generations pass, that two lightly speckled critters mated, this might produce within the litters some heavily speckled ones. When a dog has puppies, you get all sorts of patterns on the coats. So I think that's plausible. I suppose imperfect replication is enough to keep the trend going toward the heavily speckled? The environmental "pressure" is such that the lightly speckled creatures are more likely to reproduce but that doesn't mean the trait (heavy speckles) is just going to show up. It shows up by chance.As regards the issue of speciation, I'll address that in another post.Here I'm just wondering about the mechanism from lightly to heavily speckled.This message has been edited by robinrohan, 10-27-2005 01:11 PM

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.

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

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.

Any way to know why they didn't interbreed before that?

Criteria? Suppose we decide to divide life forms up according to color. So we would have red lobsters being the same species as red foxes, and brown bears being the same species as brown wasps. Now that would be arbitrary.So there's a sense in which either definition--either morphological change or gene pool isolation--is not arbitrary. Both relate directly to the causes or effects of speciation. Morphological change causes isolation and gene pool isolation leads to more differences.It's not about criteria; it's about which generation or individual we are going to pick--say, out of 40 fossils along an evolutionary branch--to represent a different species. If we use the morphological approach, we have arbitrariness as regards which we are going to pick. If we use the gene pool isolation approach, we have definite moments of isolation--which could be dated if we had a time machine--as illustrated in our example. If it can be dated it's not seamless, and we have what creationists would call a "speciation event" (the death of the last slightly speckled Eutherian).Therefore, in order for the theory of seamlessness to work, we must use the morphological definition of "species."This message has been edited by robinrohan, 10-27-2005 11:51 PM

I've been thinking about RAZD's finches, and I believe we can say that that's a case of mistaken identity. What we thought were two different species turns out to be one. But "on-and-off" is not the same thing as "seamless." However, if we use the morphological definition, it doesn't matter if we call them variants of the same species or different species. I'm sure these finches are very similar.

I would think the definition ought to be that they cannot mate. If it's a mere matter of them not mating, then 2 groups of black bears, one in Vermont and one in Oregon, would be different species.

Good stuff, Mick. I think I even understand it to some extent. Would one of those "algorithms" you are talking about be responsible for the variety of coat patterns in a litter of puppies?

You observe them. If they are adjacent to each other geographically, and they don't mate for a long time, then you assume they can't. If later on they start mating, like those finches, then you just say,"We thought they were different species; come to find out they're not."This is if you want to use the "gene pool isolation" definition. But like I said, there are problems with that definition: not arbitrary enough. It would be better to classify them using some arbitrary system about how different they are physically. If we did that, we wouldn't have this problem with the finches.This message has been edited by robinrohan, 10-28-2005 01:18 PM