> More relevant: Does it matter if human brains renew their neurons?
Yes, on a lot of fronts, but strokes, in particular, would be a lot easier to fix if the brain could renew itself. Fixing brain problems becomes much harder if the brain never regenerates.
> With 100 billion neurons we seem fine with what we have. The bigger question seems to be how to protect these 100 billion cells from degenerating.
Maybe. But we also know that those who age well seem to recruit cells from a different layer of the brain as they age. This would seem to indicate that the brain is having to "make do" for some reason which we do not understand.
In addition, what is "part of the brain"? Are the optic nerve or your olfactory nerve part of the brain? What about your spinal column? The computer scientist in me says "Of course" given how strongly linked they are with the processing.