A recent post at Amazon

This is just a restatement of what I've written many times before, though with a slightly different emphasis:

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Mutation, heredity, gene duplication and polyploidy are sources of genetic variation; it is the selection processes that act on these to form new phenotypes that bring about the genetic reduction or depletion I'm talking about. It doesn't matter what the source of the new trait is, when it is selected, when it becomes the basis of a new population of a new phenotype, whether this occurs by natural selection, or by any of the accidental processes such as genetic drift or bottleneck or simple migration of a few members of a population to a new location, new traits will come to characterize the new population thus formed, but whenever this happens it always happens with a loss of genetic possibilities to a lesser or greater extent. In fact this genetic reduction is NECESSARY to the production of a new phenotype.

The famous formula for evolution, change in gene frequencies, seems to suggest that you are just getting a new mix of genetic possibilities, overlooking the fact that to get a new trait that comes to characterize a whole population, competing alleles for the same characteristic must be reduced, even eliminated from the population altogether.

This is clearer when the selection process is drastic -- say if huge numbers of a population die while only a few have the adaptive characteristics needed for the new situation, or if a very small number of members become completely geographically isolated from the main population -- you will have a strikingly reduced gene pool in the new population from which the new phenotype develops. This is obvious, right? Sometimes the reduction is so extreme that you have fixed loci for many genes, which worries conservationists, as in the case of the cheetah. (Of course sometimes such a condition occurs in a species that nevertheless multiplies to great numbers, such as the seal population that was nearly exterminated by hunters but has rebounded to become extremely numerous; so it isn't always a threat, but the condition is nevertheless one of reduced genetic diversity which of course limits the creature's ability to vary further). It's also obvious in the case of domestic breeding, where genetic depletion becomes a serious problem with the more extreme breeds and breeders have learned to avoid such extremes. This also ought to be obvious.

I'm claiming that there is a principle here that applies to ALL selection processes, whether domestic or natural or adaptive or accidental. It is only obvious at the extremes, so that it is easily overlooked where there is gene flow and recombination that keep the genetic picture more various, where populations may be stable for many generations and so on.

But AS SOON AS some form of selection or isolation occurs, then you can see this principle in operation again, and there is nothing that can counter it. Mutation cannot counter it because the new variant is either selected or not and in either case the population as a whole must undergo overall genetic reduction in the very process of bringing about the new phenotype, whether the mutation contributed to it or not.

When you get to what is called speciation, where the new population is unable to interbreed with former populations, what you have is a new phenotype that may be perfectly viable even with severe inbreeding, but also with severely reduced genetic diversity, which is probably the main reason such populations are unable to interbreed anyway. If any variation is still possible, it's very limited from that point, and it often simply becomes impossible. Thus evolution stops. It's a stopping brought about by natural processes, by the very processes in fact that are commonly supposed to be the mechanisms by which evolution proceeds.

The problem is that evolution is merely ASSUMED by evolutionists to be able to continue indefinitely simply because we see variation happening in nature, and somehow the fact known to conservationists and breeders that the formation of new phenotypes or breeds always leads to a point where there is little or no genetic variability left gets ignored. Apparently this fact is ASSUMED to be overcome by mutation, or it is ASSUMED to be overcome by millions of years, but if the processes of selection and isolation themselves lead inexorably to a reduction in genetic diversity, this is a false assumption.

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(Funny how it's Darwin's main contribution, Natural Selection, the supposed engine that drives evolution, that is the very mechanism that makes evolution impossible.

But also, I want to note that although some are very strict about the meaning of Natural Selection as involving the survival of the adapted, as a matter of fact the Galapagos turtles didn't develop their different characteristics as a result of NS, but simple migration to a new location. Also, Darwin's finches don't need to be explained by NS either, because there are so many different types of them. Geographic isolation caused by migration is probably how those different "species" of finches developed too. This brought out the new characteristic which then found its appropriate use in the environment. )