What is the mechanism that prevents microevolution to become macroevolution?

Yes, the goalposts are high. Before Biblical Creationism or ID or YEC can be taken seriously they will have to produce models that explain ALL of the observations better than any current or reviesd models.

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Aslan is not a Tame Lion

Great point Faith.If the flood had happened, this is the kind of thing you should be able to point to as support for your model.If the flood happened we should see a genetic bottleneck in all living species where all of the indicators point to an event that happened about 4500 years ago. This would be great supporting evidence for there having been a flood (but of course no support for any theological implications). It would also be scale independent since as long as the same scale is used, every critter should show the same indicators at about the same period.If that isn't seen, then we can toss the idea of a flood on the trashheap of great ideas that just turned out to be wrong.If you ever want ID or YEC or Biblical Creationism to be considered as science you must be prepared to toss away your conclusions once they are shown to be wrong.You ready to do that Faith?

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Aslan is not a Tame Lion

That's fine Faith. If and when some ID or YEC or Biblical Creationist can show such evidence, it will be time to dust off the old flood and put it on the shelf. Once they also place the model on the table that explains the geological, radiometric, archeological, sociological data it might be worth even considering that such a flood might have happened.But three things to remember Faith.

1. The model must explain ALL the evidence better than any existing model or any revision of any esiting model or any competing model.
2. the model must be backed up by evidence which can be independantly confirmed.
3. Even if you could show that there was a world-wide flood and the resulting bottleneck, it provides NO support for the theological nature of the event.

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Aslan is not a Tame Lion

The important thing is we don't see the same bottleneck across ALL species at the same time. If there had been a Flood as described in the Bible there would be this monstrous flashing neon sign in the genetic record that would be the first thing ever geneticist in the world saw. It would be out there standing like a giant among the signatures waving at all that pass, "Notice ME!"

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Aslan is not a Tame Lion

It seems to me that we have a fairly simple and elegant way to test Faith's hypothesis.If the world is young, and if there was some Fall, and if Genetic diversity has been decreasing, then we should be able to see remarkable changes over even short periods of time.Considering humans initially.If we look at the DNA from a human from say 5000 years ago, and one from say 4000 years ago, we should see an enormous difference. If we look then at one from 3000 years ago, and 2000 years ago and 1000 years ago and today we should see an enormous difference at each step, a decrease in the size of the genome.This should hold true across all species sampled.If we look back a little further, say before the Fall or before Creation, we should see even bigger differences.

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Aslan is not a Tame Lion

Well as Quetzal pointed out in Message 79 it has been done. In his words:

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Aslan is not a Tame Lion

IMHO that is wrong because it is just a snapshot at one moment of a dynamic process. The availability of a alleles is not something set in stone but rather something that changes dynamically and constantly. While a division might reduce the population to 19 alleles, over time new ones will occur. This is particularly true in cases where a species has multiple copies of the same gene, for example MGC8902. Having multiple copies of the same gene allows critters to continue whatever the function of that gene might be while other copies might get modified to bring about some new trait.Please remember that you are just talking to a dumb layman here so it might be better to be asking folk like Quetzal or others than me, but here is my take for what it is worth.One of the big things that seems to come up quite often is the perceived difference between man and our closest cousins, the other primates.At some time in the distant past there was a split similar to what you describe. It looks like one population got a whole bunch of copies of MGC8902 and very likely did not get a copy of some other gene so there was very likely a temporary reduction in diversity. However, over time, there was an increase in diversity as some of those copies of MGC8902 were available to be modified to perform new functions.Like I said, it would probably better for you to be asking folk like Quetzal or even your wife than someone like me.

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Aslan is not a Tame Lion

But the condition afterward is neither fixed nor permanent. Life goes on. Yesterday I had $40.00 in my pocket, today I have $20.00, tomorrow I may well have $40.00 again.To say that there is a decrease in either genes or alleles related to some separation is simply trying to describe one stop on the trip as the whole journey.

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Aslan is not a Tame Lion