In short, a transitional scenario. Broca's area in language were in any sense predetermined. Importantly, CS is not part of the linguistic system per se. Very good comments. I would add only that CS itself is rather vague.
Language is indeed that, but only in the most trivial way.
And as I said in class, hierarchicality is already inherent in abstraction. And abstraction is the essence of categorization. So no need either of sequences, or of grammar, or of dominance hierarchies, in order to get to hierarchical processes. Something very like this was reported on by Feldman, et al.