Interesting. It should also be noted that the differences in wealth between different countries would presumably be larger if it hadn't been for the fact that they communicate with each other. Under-developed nations reap huge benefits from being part of the same world as, e.g. the US, whereas the US does not reap correspondingly large benefits from being part of the same world as them.

That said, one wonders if it couldn't be that it is higher GDP that causes higher average IQ rather than the other way around. Does he comment on that possibility?