What is the mechanism that prevents microevolution to become macroevolution?

Well, yes assuming that genetic diversity can never increase or that genetic diversity increases at a rate unable to combat the constant reduction in population size. This undoubtedly happens in some cases, where excessive isolation events can cause bottlenecks which may lead to extinction.The questions is - is this assumption valid and do we see evidence of this? When we look at the evidence do we see any species increasing in genetic diversity with new alleles entering the population?

I hate to be a pedant, and I agree with your position in principle, however: There is such a thing as mutation pressure: it is basically when a mutation happens in one direction more probably than another direction (that is, a reversable mutation occurs but it is more likely to occur in one direction than another). I explained it a little better in this post for those reading who are interested.

It is possible that new alelles can form without a mutation even occurring, so Faith's concept isn't entirely wrong. I don't think it has been shown to be a major source of new alelles, for reasons that might be apparant.From an encyclopedia article on recombination: Some of that isn't germane but the first part is. To simplify it has been said that recombination is the reshuffling of genes. Given where Faith is coming from I think a little more is needed (sorry if it has been brought up already).There is no process or marker which says 'this is a gene' in the DNA. So it is possible that during one part of meiosis (where the DNA is sliced up and recombined) that a gene will be sliced up. The shorter the gene the less likely that is. If a gene gets sliced up and paired with another sliced up gene with some other purpose, it might create an entirely novel gene.I can't see any evidence of this actually happening, but I might be wrong. Dawkins goes to great lengths to talk about genes as a unit of selection, and one selection pressure is for genes to not be too long, or they will basically be destroyed with this method.I'd be interested to hear from Faith and the biologists for comments on any studies or the like that have been done in this area. I believe that this kind of thing might technically known as a mutation, just as inversions and deletions are.

From what I know, Faith is happy with genetic change and mutations. It is her opinion that mutations that cause genetic change lead to a decline in viability overall, and perhaps the loss of an allele. It is her opinion that these mutations may convey certain advantages under some conditions but at a cost of the populations being less viable overall.I could be wrong, but that's how I read it.

I was not aware she ever denied that.