Converting

[Paleophyte]

No, I'm not. I'm arguing from the certain knowledge that there was no dividing line between any ancestor and their immediate descendant. What you're arguing for is something that is for all intents and purposes non-human giving birth to something that is human. Evolution don't work like that.

I think you're just playing with words now

Nope, I'm talking cold, hard realities. Sorry if you don't understand the words.

the differences between Einstein's brain and his mom's aren't really shades of grey, they're really visible, so much so that one earned the label of the most famous physics rockstar of all time, and the other, well.. the woman behind the successful rockstar.

The differences were trivial in the grand scheme of things. Albert Einstein was exceptionally talented in a very narrow speciality, a fact that may or may not have been the result of differences in brain structure. He wasn't much better than average at many things and had difficulties maintaining a marriage. The difference between him and his mother was razor thin compared to the difference between his mother and a chimp.

Granted, he didn't have an additional full blown neural system, but he would be a good candidate for the first modern human. The mother, being the metaphor for the pre modern human, was really really close, though, but still pre modern.

Sorry, but that comparison fails on so many levels. You're comparing the difference between two humans, one of whom was exceptional at physics, with the gap between a human and a chimp.

And there, you have it : synaptogenesis, a small change, provided tangible differences. Nobody is denying complex neural structures need to be already in place, they just happen to be not enough for whoever possesses them to be modern, something like the little change that happened to Einstein did.

No. You see, those structures simply won't exist to be hooked up by whatever process you want to invoke.
- There's no selection pressure to produce these structures. Quite the opposite. Complex neural structures take a lot of resources so if they aren't of use the selection pressure will be for their removal.
- Simply adding more neurons won't produce the right connections. It's like chucking microchips onto copper wires and expecting a computer to form if you just ad enough copper wires.
- Many of these systems have to work together. Trying to evolve them in isolation and wire them up later is ridiculous.

Sure, my scenario is clumsy.

Stillborn is the word you're looking for.

But it's enough to refute your illusory certainty about the first modern human being impossible.

The only thing you've refuted is the slightest possibility that you understand basic biology.

In summary, say pre modern humans have all the complex neural structures a modern human has, but with poor synaptogenesis

In summary, what you're suggesting here is analogous to making airplanes with tissue paper frames. Sure you can put in all the fancy parts but it'll never get out of the hangar. Then one day somebody finally figured out that one little engineering problem and the stealth fighter was invented. Except that doesn't work because the Wright brothers could never get off the ground.

and as a result, they can't conceive of god and religion.

Why you think this is an evolutionary advantage beggars the imagination. Even pigeons have superstition.

Suddenly some genius baby inherits their neural structures plus good synaptogenesis

Suddenly I threw enough uninsulated wire on the computer chips and the internet was born. Sorry about 4chan, that was not my doing.

and all his descendants inherit the latter property

Name Einstein's descendants. From memory.

is it that hard to see the fine line now..? can't we call the genius baby the first modern human?

In your fairytale, sure. Needs more dragons though. A unicorn would help too.

And what I'am writing here is just one imaginable scenario

Imaginable yes, biologically plausable, no.

how can one be so certain there wasn't some neurological process - of the "small change" variety - introducing the would-be modern humans to concepts that were unconceivable to them - namely god and religions

Argument from "What if stuff I don't know the words for happened to make my mythology right." Sorry, but those complex neural structures don't evolve independently and for no good reason. You're talking neuromythology here.