Hi Faith,
No, those points didn't come from a website, creationist or otherwise. I just wanted, as Percy suggested, to be sure that I understood your position correctly. I'm glad that you agree that it's substantially correct.
Let's walk through a simple but realistic hypothetical model to see how your proposal plays out. How about rabbits?
Faith writes:
it's possible that there was once some sort of chemical event that produced viable alleles -- from a built-in potential set of possibilities, however -- that has since been lost to the vast majority of living things.
So regardless of whether or not this event took place at Creation or at some later date, the end result is that there will only ever be a set, defined number of alleles for any given gene in any given population. If that is so, then for rabbits, we can take any given gene locus, say the one that codes for fur color, and determine that there are only a limited, defined number of alleles for that gene. There will be alleles for brown fur, black fur, grey fur, and so on, but no alleles that would produce green fur or purple fur. (This is highly simplified, since many genes can contribute to any given observable trait. Nevertheless, I believe that there are also plenty of traits that are determined by a single gene. And even if traits are complex enough that there are always more than just one gene involved in shaping them - say for example, a whole suite of genes involved in determining body size - that doesn't substantially change things. We can still realistically focus on the contribution of a single gene to that suite.)
Back to the rabbits. Rabbits are
diploid, just like most living things that we're familiar with. Under normal circumstances, each parent will contribute one allele for any given gene. Alleles are considered
dominant or recessive based on how they manifest in the phenotype, that is, what the organism looks like.
Faith writes:
Yes, and "crowded out" I suppose probably has something to do with dominant and recessive versions.
This is not really correct. Dominance describes the
relationship between two alleles for a single gene.
quote:
It is critical to understand that dominance is a genotypic relationship between alleles, as manifested in the phenotype. It is unrelated to the nature of the phenotype itself, e.g., whether it is regarded as ‘normal or abnormal,’ ‘standard or nonstandard,’ ‘healthy or diseased,’ ‘stronger or weaker,’ or ‘more or less’ extreme.
For our rabbits, each parent would contribute one allele for fur color to its offspring. So if grey fur (G) were dominant with respect to black fur (B), then the possible combinations are:
GG: a rabbit with grey fur
GB: a rabbit with grey fur
BG: a rabbit with grey fur
BB: a rabbit with black fur
Again, this has nothing to do with how desirable it is to have grey fur or black fur. This is simply how genetics plays out. (We're still dealing with a simple system of complete dominance, but the principle remains the same for more complex situations.)
Here it should be obvious that the possibilities are limited. Under ordinary circumstances, an organism will at most have two alleles for any given gene, and no more.
There is no place for additional alleles to hide. There may be an allele that is recessive to all the others, and so can be passed to generation to generation but only manifesting in the rare circumstances in which both parents pass on the recessive version. Nevertheless, if it exists at all, it will have to appear from time to time, however infrequently. In other words, if there is an allele for tan fur that is recessive to all the others, it will still manifest when two parents, say a BT father (who would be black) and a GT mother (who would be grey), produce a TT offspring (who would be tan).
One more time.
If an allele is "normal" it will always appear in a breeding population from time to time, even if it doesn't do so very often.
Faith writes:
I try to avoid using the term "speciation" unless inability to interbreed has resulted from the population split, but just in the loose sense of a population having developed a new phenotype after such a split, it's true enough.
So under your model, if a population splits off, whether by isolation or natural selection or some other mechanism, in such a way that certain alleles are lost, the frequency with which a given allele may manifest might change, but no new alleles will be created. Thus if we have a population of rabbits in which the allele for black fur has been lost, we may see a lot more tan rabbits than formerly, but we still won't suddenly start seeing red rabbits if there were no red rabbits before. What looks like an apparent increase in diversity (more tan rabbits) is an actual loss of diversity (no more black rabbits).
All other things being equal, if fur color doesn't contribute in any meaningful way to a rabbit's' ability to produce more rabbits, then the frequency of a given allele in a population should be determined by whether it is dominant or recessive to the other alleles for that gene. However, if fur color does matter, then the frequency of alleles will be affected by the environment. So even if the allele for tan fur is recessive to all the others, if having tan fur starts to provide a reproductive advantage, then its presence in a population will increase and you'll start seeing more tan rabbits than before. Remember, dominance is only a relationship between alleles. It has nothing to do with whether or not it codes for a "desirable" trait or is a "strong" or "weak" allele. If tan fur is an advantage, then you will inevitably see more tan rabbits than black rabbits, since tan rabbits will reproduce more often.
That's Natural Selection. In this regard, your model appears to be in agreement with the standard biological model. Alleles that produce traits that confer a reproductive advantage will become more prevalent, and alleles that produce traits that are disadvantageous will become less prevalent or even vanish.
If your model is correct, and there is no mechanism for producing new alleles, then you are right - genetic diversity can only decline and never increase. There is no source for new alleles to emerge, only for existing ones to either thrive or fail.
I'll pause here once again to see if I'm misrepresenting your position in any way, or if you disagree with any new material that I've presented.
I have no time for lies and fantasy, and neither should you. Enjoy or die.
-John Lydon
What's the difference between a conspiracy theorist and a new puppy? The puppy eventually grows up and quits whining.
-Steven Dutch
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