My argument is that reduction in genetic diversity is the inevitable inexorable trend of all natural processes towards speciation, and all species undergo these processes
My point is that it can't be a loss of alleles due to splitting the population that produces speciation.
I've said many times that it's just one of the ways speciation comes about, but all these involve change in allele frequencies. It's change in the frequency of alleles in a population that brings about new phenotypes and ultimately speciation. Isn't that a familiar formula? It's the formula for Evolution, isn't it? Evolution = change in frequency of alleles in a population. Or is that formula now scrapped?
Splitting the population is just one way to describe what the "evolutionary processes" all do. Change in frequency of alleles is brought about by isolating a part of a population, either partially or completely, geographically or through severe selection by the death of those that can't adapt to a new environment, and so on. This allows other alleles to be expressed more frequently. Even sexual selection and gene drift may be said to isolate a population in a certain sense, without actually separating physically from it but by allowing the selected features to reproduce in greater numbers and come to dominate the whole population over time at the expense of other traits.
Change in allele frequency simply means changing to more of some alleles and less of others than the original population had. Roughly, whatever allele the population has more of is what determines the phenotype character for that trait in the population. That's a high-frequency allele. You get a population of blue-eyed people when there are more alleles for blue eyes in the population than other kinds. More little b's means more pairings of little b's so more blue eyes, etc.
So, as these new frequencies work their way through the new population by recombination, a phenotype that is different from that of the former population comes about. What was previously less expressed is now more expressed and vice versa. This process affects some unknown number of genes and their alleles, depending on all kinds of things having to do with which individuals ended up where. This may not even be knowable for a given population because you'd have to study every member of the population and track its history to be certain about the numbers and frequencies involved.
Now, just considering this process alone, putting aside mutation for the moment, you will NEVER have new alleles because all you have is what was already present in the original population. You'll have only more or less of different alleles of the same collection of alleles, and MAYBE you'll actually have NO alleles of a particular kind because it's possible for those to be left out of the shuffle. They'll still be in the broader population but in the one they aren't in, that trait will not be expressed; other alleles are going to get expressed instead.
The actual effect of there being none of a particular allele may not be any more striking than an allele's existing in the population at a very low frequency, but the point is that a change in frequencies CAN involve a loss of alleles and NEVER involves the addition of new alleles. All you have to work with is what was already in the original population; again, assuming no mutation.
Over time, with many population splits, with natural selection, with geographic isolation, with founder effect and bottleneck, all these "processes of evolution" working on populations, the overall trend is going to be toward a loss of alleles in an isolated population. Those may still be present in the other populations of the same species, and if gene flow or hybridization occurs between them then lost alleles may be reintroduced, but if the population is isolated and there is no gene flow between it and the other populations, it may develop in the direction of speciation.
So something else must be needed. Especially if you make interbreeding yoour definition of speciation.
I'm just accepting the evolutionist's terms. If they want to define speciation by inability to interbreed it doesn't matter, to me that's just the extreme of this overall tendency we're discussing, that moves in that direction whether it arrives there or not. In other words, it isn't speciation as such but the development of new genotypes/phenotypes I'm focused on, that may or may not become a new species.
Without new alleles, all the alleles in the split populations were present in the parent population - yet it would be unusual to find much in the way of incompaitbilities in reproduction in the parent population - so why should the split populations be unable to interbreed unless new alleles that are incompatible are incorporated into one population or another ?
That's a logical question and I don't know. One answer MJFloresta gave is that they may be able to interbreed but simply don't for whatever reason. Speciation would be the extreme of the processes involved, by which time the frequencies of alleles are very different between the populations. Theoretically they should be able to recombine just because they all have the same basic genetic structure, same genes etc., so there must be something about the lack of fit that prevents it.
Thinking about mutation in this respect, however, why should that prevent interbreeding either? Mutation simply changes an allele, but if the basic gene is there in both populations why wouldn't the new allele simply combine with whatever other alleles exist in either population? In other words I don't see how a mutation would be any more of a barrier to interbreeding than it would be to sexual recombination within the population it occurred in. Whether the alleles in question were always there, or introduced by mutation, they have to be able to pair with others if they are going to be passed on, and I see no reason why they should have any more trouble interbreeding than inbreeding, or any more trouble doing either than a pre-existing allele would.
In other words, if alleles for the same gene can be "incompatible" at all, then what is the nature of this incompatibility and why couldn't it occur among pre-existing alleles as likely as among mutated alleles?
MJFloresta suggested on another thread that it's not that they CAN'T interbreed but that they don't, and that it should be possible to test this by artificial means. I thought that made sense. Kuresu then put up a list of known hybrids for many species which looked to me like a way to define a Kind, but at least it showed that it's possible to interbreed species you might not expect.
Yes, they are possible in the original species, but the traits of some alleles are not expressed much or at all, and could be said to be "latent," either because they occur in very low frequency or are recessive or affected by other genetic conditions I wouldn't know a lot about.
Rare alleles would be prime candidates to be lost.
Right. I lose track of what I'm trying to say sometimes. Rare alleles WOULD be more likely to be lost, that is, lost to a new smaller population that migrated from the original. Very unlikely to take the rare alleles with it. But those alleles have to end up in one or the other population and if the population split reduces the number of individuals appreciably the rare alleles will have a better chance of being expressed, in whichever population contains them.
And there must be some change elsewhere to allow unexpressed features to be expressed.
Simple reduction in the number of competing alleles, caused by the population split, is the change that would allow it. You'll get more of whatever-it-is in the population over time simply by reducing the frequencies of all the other alleles for the same gene -- unless there's some selection process working against it of course.
It doesn't seem that speciation would be very likely in your model.
It's the same model scientists use, change in allele frequencies through various population-changing processes. I'm merely analyzing what's really going on in it. I haven't added anything to the processes I've seen described in many discussions of how population genetics works. The difference seems to be that evolutionists assume mutation behind the whole thing, and so fail to notice what I'm pointing out about how it works in the direction of reducing genetic diversity -- again, without mutation in the mix.
The point is just that it is very hard to get across this fact of inexorable genetic depletion through the normal processes of variation and speciation, because mutation keeps being assumed to take up the slack of this depletion. In fact it simply doesn't.
But that has NOT been established as a fact. That is your opinion, and so far as I can tell it is based mainly on your desire for it to be true.
If you would just keep mutation out of the picture for the time being and just think through the processes I'm describing, which are all standard science that evolutionists refer to all the time, you ought to be able to follow it all to the logical conclusion I keep pointing out here, which is that genetic depletion IS the overall trend in all these processes. There's nothing of opinion in this at all, it logically follows from an understanding of what these processes actually do.
Mutation has to be able to occur at a prodigious rate with prodigiously useful effects to overcome this inexorable reduction,
You assert that, but without actual numbers it is simply an unsupported assertion. So far as I am aware there is no need for the mutation rate to be any greater than it has been measured to be.
If you want it to float evolution in the face of all the genetic-variability-reducing processes, there is.
So at what rate are alleles actually being lost ? I don't want your opinion, I want a valid estimate based on real evidence. Do you have one ? If not then are you prepared to retract your assetion ?
Well, if you would just follow the argument here, you'll have to see that what presently is credited to mutation is nowhere near supplying the number of useful changes needed, that is, the number needed to rival those changes that take place in every sexual recombination, or for that matter in whole populations as allele frequencies change over time -- billions of changes, all of which tend in the direction of decreasing genetic variability. I haven't said anything that contradicts anything in standard population genetics. They just don't recognize the implications of it that I'm trying to bring out.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.
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