Originally posted by aardvarkhome
What is the mechanism that prevents a succession of microevolutionbary changes adding up to macroevolution?
The main argument about transition from micro to macro is the comparatively small amount of empiricle evidence in support of the macro. We have and are observing changes within the lower classifications; this is no longer disputable. However, no one has observed a case of macro-evolution because it is supposedly such a long process. The next best thing is the fossil record, which shows us indirectly what has occurred. There are hypothetical "transition" fossils between higher divisions, but the record has proven to be very disappointing as far as smooth transitions between major classifications. Of course there are explanations for the scant record, but explaining them away serves dually to explain away any solid evidence that we try to draw from the fossils.
What we have beyond that is mostly comparisions among living species. Similarities among organisms can certainly be explained by descent from a common ancestor, but others can claim that it is evidence for a designer/creator.