> workings of the brain to intelligence is the tricky bit
I don't find it that tricky, intelligence does come from the brain.
> That's like equating the workings of my bicycle to my decision to ride to a particular place
Both one's brain and one's "intelligence" belong to the same person, like, physically and materially, which is not true when it comes to your bicycle example. More to the point, I find the comparison itself kind of self-describing, it's like deciding to "outsource" intelligence to some other external, non-ethereal entity (like a bicicle that is physically separate from a human being) in order to avoid those hard questions the OP was alluding to (hard questions that oftentimes also involve the political side of things).
Now I want to say that your ideas don't come from your brain. But of course they do, as a result of interaction with other people's ideas, some of which were written down. (Don't worry, I'm not a dualist.)
The thing is that no matter how fancy your bicycle, I can still ride my shitty bicycle to a university, and you can ride your lubricated carbon fiber bicycle into a ditch, and then you're not so smart. If what you call intelligence is how fast your bicycle typically goes into the ditch, then sure, it can be measured on a scale and you have more of it.
You, as a dualist, is the least of the fears we hold.
There are other notions about the transfer of ideas: https://www.apa.org/monitor/2010/06/memory-transfer
I'm not a dualist! Fumes
Wait, cannibal worms that eat memories? My my.
I for one thank our AI overlords that weight training avoided that path not taken :/