Tuesday, May 29, 2012

The Genetic Bottleneck challenge to the Flood answered again

On the thread at EvC about how a worldwide flood should have left evidence of severe genetic bottleneck in all living things, it is claimed that there is no such evidence, My answer, which I have given before here, is that they see no evidence for the bottleneck because what they are looking for is what happens to species NOW when there is a bottleneck -- such as the severe homozygosity of the cheetah.

But as I've argued here before, the evidence would simply be a great deal MORE homozygosity after the bottleneck than before, and since we have no way of knowing how much there was before the Flood we can't anticipate how much we should expect to see afterward either. But if there was enormously more heterozygosity before the Flood than there is now, say as much as 75-80% for human beings, as opposed to today's known percentage of 6.7% heterozygosity, then the reduction, the less heterozygosity and greater homozygosity today, wouldn't be noticed, it would be assumed to be normal to the species.

On the usual expectation, Dr. A gives this standard answer to the question how we might determine if there has been a bottleneck in a species:
Well, you look at the size of the population and the amount of genetic diversity within it. In equilibrium (i.e. if the population has been about the same size for a long period of time) the diversity will be proportional to the population size --- there'll be a certain quantity of diversity such that the production of new variants by mutation is just balanced by the elimination of variation by genetic drift.

If there's markedly less diversity than that, this indicates a recent bottleneck.
One clear indicator of reduced diversity is the percentage of homozygosity in the genome: the more homozygosity the less diversity. The problem is that if there was a worldwide Flood, then when you are looking only at today's populations you ARE seeing "markedly less diversity" than would have been the case before the Flood and not recognizing this. Since there is no way to measure the pre-Flood diversity you cannot make this judgment.

HOWEVER, there should be a hint in the fossil record to a much greater pre-Flood diversity, and this does seem to be the case as many species are represented by a huge number of variations. These variations are of course explained by the Theory of Evolution as stages in evolution. But if they were in fact all living populations at the time of the Flood that would in itself demonstrate a very large diversity. There were dozens of different "species" of Trilobites, for instance, and large reptilian sea creatures show an equally great amount of variety, judging from the specimens in the Karoo formation for instance.

The question of the genetics involved, however, seems to me to be most likely answered by the fact I found in Morris and Parker's What Is Creation Science? on page 112, which I quoted in a post on the subject in September of last year, where I quote Parker saying that
human beings are "heterozygous" for 6.7% of their genes, on the average. That means that 6 or 7 times in a 100, the pair of genes for a given trait differ like the genes for brown or blue eyes, or for rolling or not rolling the tongue. Now this may not seem like much. But Ayala calculates a single human couple with just "6.7% variety" could produce 10 to the 2,017 children ...before they would have to produce an identical twin..."
And I go on to comment that
He goes on to say that the whole spectrum of skin color we see today would be easily produced IN ONE GENERATION with just this 6.7% heterozygosity for that trait. Combining that with the same breadth of possibilities for size, hair or fur color, bone type, muscle type, and so on and so forth, would certainly yield an enormous variety of individuals within each created kind or type.

So I figure this 6.7% heterozygosity is what remained on average to all creatures after the Flood, or perhaps it was somewhat more then and has decreased since then. It's still enough to produce enormous variety, everything we see today.

Well, what does a bottleneck do genetically anyway? Doesn't it produce HOMOZYGOSITY for a number of traits? Isn't that what happened to the cheetah -- it has reached the point genetically where most of its genes are fixed and no variety is possible at all. Since the cheetah is of course descended from the cats on the ark, with their already drastically reduced heterozygosity -- perhaps comparable to the 6.7% of human beings -- a later bottleneck would have reduced it even further to the current state of almost 100% fixed loci, so that each individual is almost a clone of all the others, and further variation is as good as impossible.
6.7% heterozygosity as measured today under the assumptions of the ToE would be taken as the norm for human beings, but it could reflect an enormous reduction from a pre-Flood percentage and therefore represents the bottleneck of the Flood itself.

Just another of the many supposedly unanswerable challenges to the Flood and other creationist claims that have been answered quite nicely though the answer is never recognized and the same old challenges keep being repeated.

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