Here's Percy's opening gambit on the subject on that thread:
Genetic diversity can go in any direction after reproductive isolation. For example, consider a relatively homogeneous population that becomes divided in two when a river changes course. There are now two populations, both with pretty much the same alleles and allele frequency. Mutations experienced in one population will no longer be shared with the other and the populations will evolve along different paths. If this continues for a sufficient period then they could lose their mutually interfertile quality and become two species.Let's take it step by step:
Genetic diversity can go in any direction after reproductive isolation.Of course I am claiming that genetic diversity can NOT go in "any direction" after reproductive isolation. It CAN remain more or less stable for long periods, but otherwise it can ONLY decrease; it can NOT increase. This is of course based on the Creation Model I've spelled out in earlier blog posts, that denies the mutations which are needed by the Evolution Model. Mutations are the ONLY way it could increase.
But to get off the hypothetical and bring this down to a question of evidence and fact, I'm claiming that it DOESN'T increase, and that ought to be provable with the DNA sampling test I've suggested.
For example, consider a relatively homogeneous population that becomes divided in two when a river changes course. There are now two populations, both with pretty much the same alleles and allele frequency.Of course if you posit a split into two populations that retain the same character as the original I wouldn't expect to see much change either. This is not a scenario that leads to evolution and all I'm talking about is how evolution -- or variation or the production of a new phenotype -- leads to reduced genetic diversity.
This situation would exist if the two new populations are appreciably different in size and/or have appreciably different gene frequencies -- which is in fact more likely to occur in a smaller population. That's when you get the beginnings of the phenomenon I'm talking about. The larger may change too to some degree because its gene frequencies will have changed also, but not to the extent of the smaller one.
But evolution always has to invoke (beneficial) mutations, those imaginary changes in the DNA that fuel the changes the theory requires.
Mutations experienced in one population will no longer be shared with the other and the populations will evolve along different paths. If this continues for a sufficient period then they could lose their mutually interfertile quality and become two species.Of course there is no evidence that this happens at all. And the Creation Model has no need of them as there are plenty of built-in genes and alleles to bring out all kinds of variations in any Species.
1. Mutation is not needed, the original genetic endowment of each Species fuels all possible variations of that Species.
2. There is no evidence for it, it's purely an article of faith.
3. Where there is evidence of its existence, its effect is either neutral or deleterious, which the Creation Model explains as due to the Fall which brought death, disease and deformity to all living things.
If both populations thrive then diversity could increase in both.There is no way that GENETIC diversity ever increases after reproductive isolation -- not just "diversity" as PHENOTYPIC diversity is something else, and as my formula has it, phenotypic diversity increases as genetic diversity decreases. I don't know how to prove this as making charts of combinations of genes and alleles quickly gets beyond me, but keeping the Creation Model in mind ought to make it intuitively obvious. One argument I've made is that it ought to be obvious that increases in genetic diversity would prevent ever establishing a domestic breed as its character would always be threatened by the input of new alleles.
As I quote in a post below, from the Wikipedia article on Zygosity:
True breeding organisms are always homozygous for the traits that are to be held constant.Homozygosity for an entire population is of course the extreme of genetic depletion, also known as "fixed loci" in which there is only one allele in the entire population for the given gene. It's the same situation that Nature has brought about in the cheetah and the elephant seals and the North American bison. It's the FORMULA for getting a new phenotype. It's EVIDENCE that what i'm saying is correct, that you MUST have reduced genetic diversity IF you are to get EVOLUTION.
And again it pertains not just to domestic breeding but also to varieties in the wild -- the beaks of Darwin's finches couldn't be counted on to be stable even if they had been brought about by Natural Selection, they'd always be subject to change that would interfere with their relationship to their environmental niche. In other words an increase in genetic diversity ALWAYS interferes with EVOLUTION. You get evolution or the development of new phenotypes / varieties as you lose alleles for competing traits, which means a decrease in genetic diversity. For a finch population to be characterized by a beak that can crack nuts means it has to NOT have the alleles for beaks that can penetrate small narrow spaces. It could be that an all-purpose beak would work fine and dandy, but the theory says that you get these specialized beaks by natural selection so that they can adapt to their particular ecological niche and since that does appear to be the case they must have alleles FOR their particular adaptation and NOT have the alleles for the other adaptations.
I know I argued this to death on that thread to deaf ears and here I've barely gotten through this one post from Percy. Oh well, might as well keep at it for a while at least.
But if one or both populations suffer some disaster such as flood or famine or an invasive predator or disease that greatly reduces population size, then diversity would be reduced. It all depends upon what happens to the populations.No, it doesn't ALL depend on that although such events would certainly have an impact. The point I want to keep in mind here is CHANGE IN GENE FREQUENCIES. Many things can bring this about; what brings it about isn't the important thing but simple population splits are usually quite enough for the purpose.