That first link entirely ignores that IQ tests have been shown to be culturally dependent. Likewise for the aptitude tests he conflates them with.

Pretty sure if you wrote an IQ test where your standard population was a group of people living in a harsh jungle environment, urbanite Westerners would come off thick as pigshit.

Or an aptitude test for "How good are you at tracking cassowaries without being disembowelled by them".

I've read good dissections of what's wrong with Diamond's work, that link is not one of them.