Since today's topic seems to center on the vertical aspects of g, I thought I would link to Garlick's article in Psychological Review a few years ago.¹ I apologize if this was posted here before my "arrival" at GNXP, but I searched the archives and could find no mention of it.

In sum, he postulates that individual differences in g arise because of different, innate, capabilities for neural plasticity coupled with specific environmental interactions, which, of course, are non-independent.

However, it is then observed that if people differed in neural plasticity, or the ability to adapt their connections to the environment, then those highly developed in one intellectual ability would be highly developed in other intellectual abilities as well.

1. Please note the acknowledgement section of the paper. I cannot tell you how many articles I have read where Arthur Jensen has been acknowledged for his help with the paper. This on top of the 400+ articles of his own that he has published. One would be hard pressed to find a more devoted scientist to his/her field.