"But creationists never explain the magic cutoff switch that keeps all those "micro" changes from adding up to a "macro" change."
Creationists tend to believe that speciation is not attributable to evolution, so why would creationists be looking for your "magic switch?" You're unintentionally supporting your own little bogeyman there, bubba... aintcha now? LOL.
Evolution means "change." Speciation is a change. Therefore speciation is evolution. Define "macro" evolution, so I know we're on the same page.
Creationists tend to believe that speciation is not attributable to evolution, so why would creationists be looking for your "magic switch?" You're unintentionally supporting your own little bogeyman there, bubba... aintcha now? LOL.
You're entirely missing the point. Many creationists frequently claim that "sure, evolution can produce significant amounts of 'microevolution' within a 'kind', (although they never actually define 'kind' in any testable way], but it's incapable of producing 'macroevolutionary' change".
This begs the question, "oh, why not?" If, as the creationists admit, evolution can produce significant amounts of change, then *what* exactly would (allegedly) stop it from accumulating more and more changes over more time until the amount of change is large enough to produce a different "kind" eventually? In other words, creationists argue an (imaginary) dividing line between what they say is *possible* "microevolutionary" change and (impossible) "macroevolutionary" change. Okay, fine -- feel free to define the line, and explain the (imaginary) mechanism that *blocks* "microevolution" from accumulating enough change to result in "macroevolution".
Go ahead, we'll wait...
While you're at it, read my prior post and look at the "fish to elephant" transitional fossil sequence. Feel free to point out the two consecutive fossils which are so different from each other that no creationist would write them off as just "microevolutionary" change. Can't find any? Neither can I. Okay, then, what magical process prevents those several dozen "microevolutionary" steps from occurring one after the other to eventually result in the indisputably *MACRO*evolutionary change of a fish lineage evolving into elephants over 400 million years of accumulated "micro"evolutionary transitions?
Uh, no they don't. Or, rather, 19th Century creationists mostly believed in fixed and separately created species, but modern creationists are invariably offended if this anachronistic view is attributed to them.
It's generally uncontroversial among creationists, for example, that all living horses and asses are probably related by common descent. (This is one of the frequently cited examples of a likely "created kind".) And note, by the way, that many of the species in this Family have widely differing chromosome numbers -- a difference not attributable solely to simple allele shifting "micro" evolution.