Friday, August 29, 2014

Selection always reduces genetic diversity

UPDATE 2, 8/30: I figured out what PaulK meant and I do have to admit that it's odd I didn't know what he meant right away. Of course he simply meant that it is conceded that selection reduces genetic diversity but that this is corrected by mutations. Yes the greater part of the arguments about this issue were about whether mutations could actually do this. I guess it's odd this isn't the first thing that came to mind and the only explanation I have is that I could never take that argument seriously.

It's purely hypothetical for one thing, whereas the reduction in genetic diversity brought about by a population formed from a reduced number of individuals, by selection or any other cause that isolates such a daughter population, isn't in question at all. In the end it's an empirical question that can only be answered by some kind of empirical test, such as the laboratory test I've often suggested.

I've made a number of objections to the idea that mutations could make a difference, one being that if they did they would only interfere with the phenotype formed by the selection or isolating processes, another being that useful mutations don't occur frequently enough to make a difference anyway. And so on. The idea that mutations do anything useful, that mutations are the cause of all the functioning alleles in all species for instance, is pure theory, and utterly ridiculous theory too, because it's impossible.


UPDATE 1, 8/30: Occurred to me that maybe PaulK was saying I was wrong to say that they fail to take the loss of genetic diversity into account. If so he'd have to show where anyone did take it into account as all I recall is endless arguments about this. If one or two did concede the point it must have been after all that argument AND I'd guess it was a highly compromised concession. But since he doesn't explain what he meant, who knows?



And since I've been accused of lying, I'll just take a moment to answer this one too, Paul K in Message 452 :
[I said} (Over and over they fail to take into account that you lose genetic potentials or information with every selection event, which is OBVIOUS, PEOPLE!)
[And PK answered] No Faith you know perfectly well that that's not the case. But that's typical creationist behaviour, Unable to support their argument they just grossly misrepresent the opposition.
Well, farther up thread Moose gave an example of natural selection in which the catching of large fish in fishermen's nets eventually led to the population of fish being characterized by smaller fish. At the time I noticed that he didn't take into account that of course the genetic diversity was reduced, meaning now there are fewer genetic possibilities of larger fish being produced in the population. Perhaps it hasn't been reduced to NO possibility, as whatever combination of genetic material is necessary for the larger version may still be possible in the population and could even be selected under future conditions. But the point remains that the current selection event of removing the larger fish has also removed or severely reduced the genetic basis for the larger size fish from the population as a whole. This HAS to happen.

Paul K loves to accuse me of knowing something I'm denying but as usual I have no idea what he thinks I'm denying.  There have been many attempts to answer this claim but I haven't found any of them convincing.  The answer usually given to my argument that genetic diversity has to be reduced by selection is that it is not actually observed. But the only actual example anyone gave for that was the rapid spread of a small number of rabbits introduced into Australia, whose genetic diversity is supposed to have increased along with their numbers. By observation. But this cannot happen. If you start with a small number of individuals you are starting with a gene pool that is severely reduced in diversity. And by the end of that discussion somebody had even raised a doubt that the actual facts about the original small population were true at all.

There is no way that you are going to increase the genetic diversity of a population that starts out with severely reduced genetic diversity which is always the case when you start with a small number of individuals. The cheetah and the elephant seal are cases in point. Both have apparently thrived in spite of their depleted genetic diversity but nothing has occurred to increase that diversity. By all known genetic standards it cannot happen. The usual idea is that mutation is the way new genetic material arises, but everyone concedes that beneficial mutations are extremely rare. The cheetah could wait a very long time to get a mutation tnat would improve its severely depleted genetic diversity.


And to Percy:  When I use the word Plausibilities I'm talking about the plausibility of a theory or hypothesis or interpretation.  Perhaps Probability should be left out of it as it relates to another subject.

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