Converting

[Paleophyte]

That isn't how evolution works. You get tiny, incremental changes over thousands of generations.

I think you're underestimating the effect tiny changes can cause, especially when they involve the brain. It's well known that the smallest brain incison might cause huge impairement in speech, memory, etc.

Trust me, I'm not. You're talking large changes through the introduction of a small defect that disrupts communication between some very complex neural systems. You can do that. What you can't produce is enormous leaps forward through a small improvement that connects a bunch of complex neural systems. You need those complex neural systems to have evolved in the first place and there's simply no selection pressure to produce a non-functional brain structures that do sweet bugger all except wait to be connected at some future date.

It's not excluded then that our brains "became modern" as a result of a seemingly insignificant change in our neurological system.

Yes, it really is. Aside from adding a few hundred cc's of brain matter you'll need to produce a whole shitload of hellishly complex and entirely new neural systems. There's simply no doing that without a few thousand generations of intermediate steps. You'd have better odds of going from a hand-drawn cart to a Porche in a single leap.

I mean, we had to become modern at some instant.

No, we didn't. This is precisely where your thinking fails. The whole "modern-primitive" false dichotomy ignores all the intermediate steps. Your "narrative" fails to see the shades of grey because it was written by priests who knew absolutely nothing about evolution or biology. It is this ignorance that demonstrates a complete lack of divine inspiration or authorship.