What is the mechanism that prevents microevolution to become macroevolution?

So you accept that adaptation through changing allele frequencies in reaction to selection pressures is possible, unless the changes in allele frequency are due to the introduction of new alleles (mutations), in which case the possibility of adaptation is questionable?--Percy

So all you're looking for is evidence that mutations happen on a significant, regular and consistent basis?Or are you looking for an explanation of how a point mutation (single nucleotide substitution) is actually the same thing as a new allele?--Percy

No, you're right about that. Think of a gene as one slot on a chromosome. Each chromosome has slots for lots of genes. Each gene has a number of alleles that can be plugged into its slot. There is no requirement that all alleles of a gene be the same length in terms of nucleotides, but it would probably be generally correct to say that most alleles of the same gene are approximately the same length.Each allele of a gene consists of a sequence of nucleotides. A point mutation is when a copying error causes one of the nucleotides to be incorrect. It would be like changing one letter of the word COW to get SOW. Continuing the analogy, whereas before the mutation the allele performed the action "MILK THE COW", after the mutation it performs the action "MILK THE SOW".So the question is, are you looking for an explanation of how a point mutation (single nucleotide substitution) is actually the same thing as a new allele? If so, then I think I just provided one.--Percy

I haven't participated very much in this thread, but since it is ending soon I just want to note that I don't think the topic of this thread has ever been addressed. There's been a lot of discussion about mutation, but as far as a mechanism preventing micro-evolution from becoming macroevolution, nothing.If this topic comes up again I think the creationists need to better understand what they're claiming. An analogy would be micro-walking versus macro-walking. What keeps a micro-walk from becoming a macro-walk. Well, if you live in the continental United States, nothing prevents this. If you can walk to the store then you can walk across the country, it just takes longer. But if you live on a small desert island then the island's coastline is the limit of walking, and it makes macro-walking impossible.Just as an island's coast prevents macro-walking, creationists have to identify some boundary or mechanism that prevents macroevolution.--Percy