[Protagoras]

How could many small changes over a long time not add up to a large change?

One can change incrementally and greatly without changing fundamentally.

[crail]

How much change are we allowed before it becomes fundamental? How is change stopped before this point?

Here's what I would argue if I believed in ID. God created the species close to how they are now x many years ago, as described in Genesis. Since that point they have evolved and changed and new species may have arose. As an evolutionist, I think it would be hard to argue against that because it's irrefutable. (Irrefutable doesn't mean there is evidence to support it over evolution however.)

Otherwise, you have to address how divided subpopulations of a species evolve more or less in parallel, at least parallel enough then when the division between them is removed, they can still interbreed.