All species are transitional

Yes and we are discussing it and debating it. And my point is we want something arbitrary, once you get beyond the first round of generalities. But gene pool isolation is not arbitrary. RAZD and I have already proven that. So we need another one which is more arbitrary. In point of fact, evolution is seamless and we want some definition that will represent that fact more accurately. Gene pool isolation, being datable, will not do.

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

It's very important for political reasons. We must act. We must be able to explain to the people that there are no such things as "kinds." The way to do that is to show the seamlessness of the evolutionary process. You can't do that by defining species as gene pool isolation.

or that there is one kind: life.

I am happy to report, RAZD, that the ancestors of you and me and the cat made it through that terrible time. Due to only one mutation and various subsidiary effects (feedback mechanisms, hormones, and the like), we were able to become heavily speckled enough to keep hidden from the bad guys, and mighty bad they were too. There were many trials yet to come. And through all the horrors of being meals for predators (they found us delicious--we tasted just like chicken), we made it through. And then one bright sunny day, someone had a thought--another puzzling development--and human life began.All the rest is history--the history of grief.This message has been edited by robinrohan, 10-28-2005 09:35 PM

Probably a waste of time trying.The people who are committed to kinds are also the people who are committed to ignoring any evidence that doesn't agree with them.

a grief history of time?

Very good, RAZD.I'm sitting here with my cat--she likes to get up by the keyboard--and I wonder why we can relate so much to these creatures. The cat turns to me, and I interpret her look: "You old fool; did you not know that we are relatives?"And I thought about all the pain of history. Life is set up such that the only way to survive is to feed upon other life forms.The horror! The horror!(sorry--off-topic).This message has been edited by robinrohan, 10-28-2005 10:25 PM

No, we don't want something arbitrary. We want something hard and fast and specific and unambiguous and objective, but reality forces arbitrary criteria upon us. In this case, the continuous nature of species change means we can't unambiguously identify the dividing line between species. There will always be arbitrary aspects governing where we place those dividing lines. And again, by arbitrary I do not mean random and capricious. I mean sensible well thought out and supported criteria about which there is no unanimity and about which people disagree. What happens many times is that people recognize that no objective dividing line can be established, but they recognize that one is needed, for purposes of classification if nothing else, so they establish an arbitrary dividing line. Of course it is. Do people agree with you that permanently separating two identical populations in space or time so that they can no longer experience gene flow makes them two different species? No, they don't. Your choice of this criteria is therefore arbitrary because you can advance no better reasons for using it than other people can advance for other criteria. (In reality, gene pool isolation is a very poor criteria, and we can get into the reasons for that if you're interested.) Can't make any sense of this.--Percy

Percy, I did not choose this criteria. On the contrary, I am trying to show that this will not do. What will do is an arbitrary definition, and that is the only one that will do.This message has been edited by robinrohan, 10-29-2005 08:24 PM

Okay, I think I'm getting closer to understanding your view. You believe that valid criteria must be arbitrary, and that for this reason gene pool isolation is a poor criteria.First, about criteria. No, we don't want them to be arbitrary. We want them to be as concise and objective as possible. Unfortunately, the real world forces arbitrary criteria upon us. For example, is this color red? For this discussion, assume the wavelength for red is 700 nanometers. If the wavelength of the text measures at 701 nanometers, is that red? How about 700.1? How about 700.01? At some point an arbitrary decision about precision must be made. Maybe we decide that everyone should invest in expensive wavelength analysis equipment and that a color should only be considered red if it measures with a wavelength between 699.9999 and 700.0001 nanometers. Or maybe we decide that accuracy isn't important and that any color between 680 and 720 nanometers should be considered red. These arbitrary decisions are not want we want. They are forced upon us by real world considerations.Second, about gene pool isolation as a basis for establishing criteria for species categorization. While it would serve us poorly as the sole criteria, it *is* arbitrary. The different opinions about it represented in this thread are proof that it falls prey to the same exigencies of reality as other criteria.I'm still getting the sense that your goal is to remove ambiguity from the species classification system. This isn't possible, as everyone has been trying to tell you.--Percy

Just because there are different opinons, this does not mean that the definition is arbitrary. It just means that it is a debatable topic. I'm trying to install arbitariness as the only realistic definition. Because if it's not arbitrary, it's not seamless. If it's not seamless, then there are speciation events. I'm arguing that there is no such thing as a speciation event. Under the gene pool isolation definition, there are. In fact, I believe that they are inevitable, always, according to that definition.This message has been edited by robinrohan, 10-30-2005 07:45 PM

Hi Percy

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And the whole reason for this is that species change occurs in tiny immeasurable steps. It simply isn't possible to point to a step and say, "Before this step it was X, after this step it was Y."

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Perhaps a bit picky but this is not necessarily true. One can very clearly measure changes within species over time. Each base change, epigenetic modification etc. in every individual could (in theory) be characterized for each generation. Richard Lenski's 20,000 generation bacteria studies sort of do this and one can both demonstrate change over time and make predictions about what changes and how they will change under experimental conditions. The issue is that when one sees change over time, one cannot be sure it will lead to speciation. Often it is because we do not know what the selective forces are that are operating as opposed to not knowing what types of changes are occurring.I agree that defining species is an arbitrary concept. There are some simplistic idealized concepts in use of separation of populations that probably do not not represent any real world situations...much like other useful idealized conditions such as Hardy-Weinberg equilibrium which may never occur in a natural population. But it serves as a baseline. Trying to rigidly define a continuous process into discrete steps is always going to be a challenge.

Yes, it does. As I've explained a couple times already, you're using the wrong definition of arbitrary. The definition I'm using, and probably that everyone else in this thread is using because it's the one that applies to this situation, is "based upon individual judgment." Because the judgement of where the dividing point between species differs between qualified individuals, that dividing point is arbitrary. Then it sounds like we agree, it's just hard to tell sometimes. We can't unambiguously fix a point where one species becomes another, and that is because of the continuous nature of species change. I don't think so, but I suppose it depends upon how you define it. Point me to your definition of "gene pool isolation". Since there's no such thing as perfect isolation, you'll have to make an arbitrary (please apply the proper definition for this context) decision about how much isolation is required to qualify under your definition.--Percy

Gene pool isolation occurs when there is no more and cannot be any more gene flow between two groups. In the example, we ended up with 3 groups, unspeckled, lightly speckled, and heavily speckled. The genetic connection between unspeckled and heavily speckled was the lightly speckled. When the last lightly speckled Eutherian died, there was isolation between the other two groups. This happens at a particular moment in time. But that's misleading. If we had a different definition, having to do with morphological change, then we might call the two groups variants or we might call them separate species. It wouldn't matter. The designation is arbitrary. This is more in keeping with the real process of evolution.RAZD mentioned the possibility that later on the members of the 2 groups might start interbreeding again, due to hard times, like some finches he mentioned did. If that happens, then the earlier designation that we had 2 separate species would be seen to be mistaken, according to the definition I'm using.

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RAZD mentioned the possibility that later on the members of the 2 groups might start interbreeding again, due to hard times, like some finches he mentioned did. If that happens, then the earlier designation that we had 2 separate species would be seen to be mistaken, according to the definition I'm using

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I don't think this works very well. You may have heard of hybrid zones where the ranges of two species overlap and they interbreed. Often, though not always, the interspecies hybrids are sterile. The species interbreed when given a chance and in some cases, like African elephants, there can be introgression of genes from one gene pool to another. But it is not widespread and in all other characteristics the two groups continue to diverge in morphology and behavior. By your definition of separate gene pools, they are one gene pool. But the genetic differentiation between the two groups overall suggests that they are species and introgression is range restricted, occurring only where the two groups overlap..and still, not often. Even gene pools separated by millions of years can potential mix like the single hybrid produced by a female Asian elephant and male African elephant..they are different genera! A similar type of hybrid zone exists for baboons. I think the best studies are in crickets however. All sub-generic designations will be arbitrary because the process of speciation is continuous.