Sorry for the very long post again, but yours seem to require it.
I don't "invoke" speciation at all, I'm merely making a concession to evolutionist terminology HOPEFULLY for the sake of communication because I know it describes a real event although I don't believe it's what evolutionists think it is.
This is probably the most important thing to clear up. You say that speciation represents a "real event," but you "don't believe it's what evolutionists think it is."
It's the point at which a new variety of a species has become incapable of interbreeding with the rest of its kin.
Evolutionists call it the making of a new species, call it macroevolution and so on, but there is nothing about it except inability to interbreed that sets it off from others of its kin. So I think of it as just a portion of a species that has become isolated from the mother population and developed new characteristics that distinguish it from that mother population and others of its relations, along with the inability to interbreed with it or its siblings.
So what do you think speciation is? Here's a very simple definition that most would agree with from Answers.com:
speciation (sp'sh-'shən, -s-)
n.
The evolutionary formation of new biological species, usually by the division of a single species into two or more genetically distinct ones.
If this is not the definition of speciation you're using then please tell us your definition.
No problem with this definition, it’s pretty much the one I’ve been using all along here, but also to describe the formation of varieties and breeds. What they call a new species I’d simply call a variety myself left to my own devices, a variety that has stopped being able to interbreed with the rest of its family, but I use the term species because you all do.
When you get a mutation, Percy, don't you expect it to replace an allele?
Well, yes, but I wouldn't say this the way you did. I think you already have the proper understanding, but because of the way you used the word "replace" without qualification allow me to clarify so just we're sure there's no misunderstanding.
So do I expect a mutation to cause one allele to become a new and different allele in that specific individual? Sure! But that mutation to that allele in that one individual does not change that allele in all the other individuals of the population. The population continues to have that allele. What the mutation has actually done is increased the number of alleles for that gene by one. If there were, say, 17 alleles for that gene in the population before that individual experienced that mutation, there are now 18.
No problem with that description at all. I may at times get careless and forget the context of such points in the heat of argument though I don’t recall having done so in this discussion.
Lets call the gene X, and let's say that gene X has alleles X1 through X4. During reproduction a mutation changes allele X3 into a new allele that we'll call X5. Let's say that the original allele X3 is possessed by 20% of the individuals in the population, then after that newly born individual experiences a mutation changing their X3 allele into a new X5 allele, the original X3 allele is still possessed by 20% of the individuals in the population. The X3 allele doesn't go away. The X3 allele isn't replaced by the X5 allele, except in the individual that experienced the mutation.
Yes, you’ve increased diversity.
So now that we've got the clarification out of the way, let me move on to what you say next about mutations, because that's very important:
So in your example with the A-1 thru 4 and B-1 thru 4 down to Z-1 thru 4 if you get mutations to that population aren't you going to get A-5 and B-5 down to Z-5, new alleles for each gene, and aren't all those just as genetically compatible as the original batch? If they're an allele of a gene for fur color all they can do is give a new color, it's all perfectly compatible with the genetic picture already there.
Of course mutations DO change things around more than that and destroy genes and make differences between populations that way too, but isn't what I just said the basic idea about how they replace alleles?
As far as point mutations and other small mutations changing alleles into new alleles, yet that's correct.
In other words, it isn't really a big change, it contributes a new color to alleles for color, or makes little if any difference at all, and so on. Although I don't know why this is a "small" mutation if it actually makes a new allele. It is hard to wrap one’s mind around what an allele is if a change in a small PART of one can constitute a new allele, since a gene and its alleles can be thousands of nucleotides in length.
But over time as mutations accumulate and selection pressures operate the character of a gene may change. As RAZD pointed out, an allele might begin with alleles X1, X2, X3, X4, but over time the environment changes, causing the selection pressures to change. New alleles in gene X can gradually change the character of the gene so that after a number of generations we no longer have alleles X1, X2, X3, X4 but a completely different set of alleles X17, X42, X51, X63.
This is an aside, but I have to comment that there's something awfully teleological or Lamarckian about this way of describing selection, as if whenever the environment changes, mutations to deal with it just sort of come along and save the day.
Second aside is that it's obviously hypothetical and you don't know if this happens in reality or not. How much is really known about all this as opposed to being merely assumed or hypothesized?
And third, the numbers getting so high suggests that there are that many different alleles possible? But you can still only get alleles for whatever the gene does, right? Or would X51 probably not do anything new, or do the same thing other alleles do?
What is the significance of changes to the character of the gene? Well, if we take the familiar example of the bacterial flagellum, perhaps gene X originally created one of the proteins for a celia, but now the alleles of the modified gene X create a protein that helps the celia twitch a bit, turning the celia into a potential incipient flagellum.
But of course mutations do far more than just modify alleles, and one of the most common and important mutation types is gene duplication. Reproduction is a much more dynamic process than is typically imagined, and genes can move positionally around the chromosome. Mistakes can happen that cause genes to be either eliminated or duplicated. Losing a gene can be catastrophic, of course, but gaining a gene that's an identical or near copy of the original gene often has little or no effect.
What's important to understand about gene duplication is that one of the genes is free to mutate for other purposes. Research indicates that gene duplication followed by the duplicated gene mutating to acquire a new behavior (e.g., code for a different protein) are extremely common in the genetic history of life.
I don’t understand what point you are making here.
About the cat family example, the reason I introduced that example was because your scenario does not explain where the cat family came from. Not all cat species have the same genes. This could not have happened in your scenario if cats are just one kind because your scenario disallows the creation and deletion of new genes through mutation.
No it doesn’t, Percy. I thought I cleared that up in the last post or two. If they occur, then they occur. It would simply be a question how to interpret them. I
would be most likely to interpret these events as a pathology within my model unless it can be shown that they contribute something essential. I could certainly see that such differences would account for a barrier to interbreeding -- as to whether that’s part of God’s design at Creation or reflects deterioration from the Fall I don’t yet have an opinion. That is, in my model everything is either there by disease or by design, and without knowing more it would be hard to say which it is.
The main thing here is, except for my argument about reduction of genetic diversity by the processes of selection, isolation etc., I don’t have a well-worked out model for how things came down from the ark, only a loose collection of possible hypotheses, subject to change with new information as I learn it. Since I didn’t come here to argue this I’m just having a good time putting together some ideas that might fit as they come up and it’s been very informative so far, but nothing is hard and fast in my mind about any of it.
In other words, it’s not relevant to this current discussion.
That IS where they came from. They simply started with so much more genetic diversity it's taken millennia for it to get even near to running out. We are now in the days where it can run out for various species.
But where are the extra polyploid chromosomes where all this extra genetic diversity supposedly resides?
I don’t expect to see them; I don’t know why you do.
We don't see them in the nucleus of most species we look at. Mostly duplicate chromosomes appear in just some species of flowering plants. Since some species have short generation times and some long, species with longer generation times have not had as much time to lose these extra chromosomes, and they should still be there in at least some species, but they're nowhere to be found.
But you are making assumptions it is not necessary to make. It may not be such a direct function of time but the effect of splitting, isolation, destructive mutations, selection and drift and random environmental factors, all different for different species in different times and places.
If we were to take a completely blank slate approach with no preconceptions then we could say that there are two ways existing species could have arrived at the current genetic composition. One is that they began with huge diversity stored in polyploid chromosomes and have gradually lost that diversity over time. The other is that the have evolved according to evolutionary theory, with selection pruning variation according to the environment and mutation continually adding variation and initiating trial-and-error experiments for selection to play with.
Yes, I also think in terms of these two different scenarios.
What test or experiment or set of observations can you think of that would allow us to choose which scenario is the one that actually happened?
I don’t have a test for this. I’ve barely put together a few ideas about how it might have happened. It isn’t what I’m arguing here. It’s a very interesting topic but it’s all very hypothetical at the moment. I’d like to read up on some creationist scenarios for one thing, and just get more ideas from discussions such as this one about possible genetic facts that could apply.
This isn’t my argument here, Percy, and I’m not sure why you are bearing down so hard on it. Whatever the theory about it all turns out to be, I’m still quite sure that reduced genetic diversity is how new varieties are formed. And I don’t have a way of proving that either, although I have suggested an empirical test and wish it were practical to carry it out. Only more DNA-sequencing than is practically feasible would prove it one way or the other. But since most of the answers about this argument so far miss the point I can at least keep trying to get it described.
That's how new varieties are created, by new combinations of alleles in new frequencies brought about by reduction of numbers and diversity.
What evidence leads you to believe that increased variation results from diminished genetic diversity?
Uh oh, careful with that phrasing. Not "increased variation" but "new varieties." Mutation, if it works at all as claimed would produce increased variation, but it's selection et. al. that produces new varieties / breeds /races/ species.
And what evidence leads me to believe that NEW VARIETIES result from diminished genetic diversity?
Answer: How the simplest Mendelian genetics works:
If you start with a population of millions with the classical Mendelian distribution of blue-brown eye color (ignoring other genes that affect eye color) and two hundred people sail across the ocean to found a colony in a wild new land, 195 of them having blue eyes and five brown, then within three months of arriving in the new land the brown-eyed five all die without leaving offspring along with 75 of the others, within a hundred years of its founding the new colony will be made up of nothing but blue eyed people. If circumstances are more or less congenial and most of them are youngish couples, they could double their population in twenty years and increase it rapidly thereafter so that after a hundred years they could easily have well over a thousand population, maybe more, and they’d all have blue eyes. And the reason for that is simply that
they don’t have the B allele among them -- principle of genetic reduction in action in the simplest possible example.
They’re also likely to have developed a more or less homogeneous look from their inbreeding after a hundred years, even if all the originals were quite various, become a race which is what we call human varieties, and even more so as more time elapses and more inbreeding occurs. They’ll look like NewWorldlings instead of OldWorldlings. Then eventually unfortunately they’ll also start developing genetic diseases as the Amish have.
But anyway, that’s the simplest possible picture of how you get a race or variety or breed by genetic reduction. And this is how I think of the commonest forms of domestic breeding too. It’s simply a matter of selecting animals for particular traits and keeping them from breeding with animals with other traits. Again, a process of elimination, not addition. Which doesn’t discount the possibility of mutation, but does make it rather superfluous. And now that people understand better the dangers of inbreeding they may look for outcrosses to breed into their line to reintroduce some genetic variability and try to improve the animals’ genetic health, but the principle is demonstrated — to get the new type you eliminate the undesirable types and thus reduce the genetic diversity.
Dr. A answered this with the example of the American Curl cat, but as I read up on that cat I see that it has ONE dominant allele for a curled-back ear and it’s SO dominant you can easily produce cats with that trait, you don’t even have to police the matings that carefully. But this isn’t the typical way breeds have been developed. They’ve often been taken to genetic excess in the attempt to get something truly original or pure which has compromised the animal’s health. The American Curl doesn’t seem to be in danger of that sort of thing unless someone decides to develop a pure Curl specialty breed with a particular color coat along with the curled ear or something like that, which would require an extreme reduction in genetic diversity.
Mutations DO cause destructive effects and change things in ways I suppose they didn't used to.
Mutations are just reproductive copying errors. What evidence causes you to think they are different in character today than they were in the past?
It’s a hypothesis based on my Creationist overview, and not part of the current argument, simply a side comment. Musing out loud within the parameters of the Creationist overview. My understanding of the Creationist overview is at least pretty consistent even if unprovable so far. Consistency should count for something in the making of a hypothesis. Perhaps I shouldn’t sound so certain even if I AM certain. But I’m not proposing it as part of this debate, it’s just a hypothesis-in-progress.
They've become subject to deleterious mutations in the last millennium or so, that's all.
What evidence leads you to believe that mutations have been more deleterious during the last millennium than they were in prior millenniums?
More musing out loud in the context of the side discussion about the Creationist overview, again too assertively I suppose. There is no evidence that could prove this one way or the other that I know of. But when I do know of some I’ll let you know. Meanwhile, it isn’t about the topic of this thread.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.
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