It’s more or less pointless to worry about physical or neurological mechanisms in this context. Psychology isn’t really a science, but done rigorously it is a l

It’s more or less pointless to worry about physical or neurological mechanisms in this context. Psychology isn’t really a science, but done rigorously it is a legitimate phenomenology. For practical purposes it doesn’t matter what causes g or d to have the value that it does, only that various correlated behavior patterns are observable. For example the NFL and US military both successfully use tests of g to select more capable recruits. Unfortunately I don’t believe any test of d will be useful, except maybe in very low g high d individuals. This is because there is usually no incentive to score low on a g test, but there is on a d test.