My point is that there's not much differentiating us from primates besides scale, remember. I mentioned the cortex particularly in relationship to neurogenesis, not in relationship to primates. It is the most striking difference between primate brains and those of other animals. I also didn't say there wasn't any neurogenesis in the cortex. There might be, but it's proving pretty hard to find. If you read your reference 3, you'll see this:
The number of migrating cells in the
Gould et al. study5, calculated from case numbers
8 and 9, and after a single BrdU injection,
is more than 10,000 per day33. Even if only
25% of BrdU-labelled cells were neurons, as
has been estimated more recently34, the resulting
migratory stream would still be large
enough to be readily detected in the frontal
lobeswith any light microscopic method, but
it has never been observed.Moreover, if most
new cells degenerate between 2 and 9 weeks
after their birth34, then many pyknotic neurons
commensurate with the massive cell
death would be expected.This prediction has
never been confirmed.
That's the very paper I was referring to when I said "Indirect hints of neurogenesis in the cortex have been reported, but other methods that should turn them up haven't, so the evidence is contradictory." It might be there, and it might not. If it is, it's difficult to detect, much more so than the known neurogensis in older parts of the brain that is known to exist in a wide variety of species. It's also difficult to understand what role ongoing neurogenesis would have in providing some kind of "spark" for intelligence.
I doubt very much there's a magic bullet for intelligence hiding in the human brain. Your friend said it herself: "there is strong evidence that the human brain is a scaled up primate brain." The principles are the same, but there's more of everything.