Their control is supposedly higher income households. But that doesn't prove causation. It could be the smarter people tend to earn more.

I had a black family that lived across the street from me as a kid. The dad was an industrial engineer for a major corporation. One of his sons is basically a genius. He has a Ph.D in engineering and started and runs a company that designs and builds medical lasers. The other son used to literally drool on himself to the point that his parents bought him hypercolor shirts so he could say the drool stains were due to heat changing the color. Genetics matter.