[ziggygrey]

What does an IQ point measure? What definite, measurable, objective biological quantity does it represent?
Synapse speed?
Neurons firing/second?
Brain current?

[edsheppa]

You didn't get the point. If IQ test results are correlated with definite, objective measurable phenomena then it is stupid to say it isn't real.

What does it measure? Well, in the case at hand, it is a statistical measure of the growth function of the cerebral cortex in children.

The import of your post is that we must have a reductionist explanation of IQ or it isn't real. That is a misconception. If we were to accept your requirement, temperature wasn't real until we had a reductionist explanation in terms of the atomic theories of matter and all those guys with their thermometers were deluded.

In fact, if we were to accept your requirement of reductionist explanations, there could be no science. Every scientific theory must have undefined terms.