> The way human IQ testing developed is that researchers noticed people who excel in one cognitive task tend to do well in others - the “positive manifold.”

I'm pretty sure that this is not true, and that the tests were developed to measure children's intellectual development, and whether they were behind or ahead for their age. A bunch of people saw them and decided that it was far better than the primitive tests they had devised in an attempt to limit immigration from southern Europe, or to justify legal discrimination against black people, and wished a universal intelligence scalar into existence.

They justify this by saying that the results on this year's test correlate with the results of last years test. They are not laughed at. The thing it most correlates with is the value of your parent's car or cars.

That's my recollection, too--IQ was developed to judge kids' "mental age" (how far ahead or behind they are compared to their peers in their current grade) and was only later retrofitted onto the g factor model of intelligence.