Lots of people loathe IQ research. But even people who are open-minded about IQ often puckishly say "So what?" It doesn't really matter if the IQ is the main determinant of earnings, or economic growth, or anything else. All that matters is whether the marginal effect of policy on the variables we can change is worth its marginal cost. Thus, it doesn't really matter if IQ matters.
But this response overlooks a basic point. If IQ matters, then analyses that ignore IQ will typically overstate the marginal effect of other variables.
Simple example: If you statistically estimate the effect of schooling on earnings without controlling for IQ, you get a large coefficient. In the NLSY, for example, you'll find that one more year of school raises earnings by 12.6%. If you control for IQ, however, the coefficient on education plummets to 7.5%.
Does it matter that IQ matters? Of course! An investment in education that looks extremely profitable if you don't control for IQ could easily be a big waste of money. The reason: If you don't control for IQ, you are giving education a lot more credit than it deserves. To say "Let's focus on the things we can change" dodges the hard truth: After you adjust for what you can't change, the things that you can change may give you very little bang for your buck.
Thus, IQ is highly policy-relevant after all. The left-wing ideologues who damn anyone who even thinks the letters "IQ" are actually on to something: IQ research does turn out to be a rationale for "right-wing" laissez-faire policies. The more IQ matters, the more likely it becomes that existing government policies are a waste of money - and that you would get a bigger payoff by doing less - or maybe nothing at all.