There aren’t a lot and they all have some limitation. Probably the largest sample size in a study is one of the oldest: a 1937 study by Witty & Jenkins. I want to say it had more than 500, but it wasn’t nationally representative. It looked at students in the Chicago school system. IIRC they were gifted students. But it was limited to the methods available at the time. They had to approximate the students’ white ancestry via interviews and family histories, so it wasn’t precise.

In the 70s, they started using blood tests. I know that Sandra Scarr the lead researcher for MTRAS did an admixture study a year after it that leaned toward environmental.

There’s also the post WWII Eyferth study that looked at the lives of half-black children of GIs raised in Germany that found they were roughly the same IQ as white children.

Then there’s Elsie Moore’s transracial adoption study in 1986. There are probably a few I’m missing but I think there are five to seven major ones that are directly relevant to the debate and only the MTRAS can come even close to having a hereditarian interpretation.

But again, we have to work with what we have. The question could probably be settled beyond the shadow of a doubt, but I just don’t see that study getting funded because it really doesn’t have a lot of scientific value.

The only thing stopping intelligence researchers from declaring hereditarianism dead is the lack of a strong alternative explanation, and research dollars are being directed toward that end. As they should be.

The flaws in admixture studies notwithstanding, we have enough to go on to say that a genetic explanation for intergroup differences is doubtful even if we can’t say for 100 percent. If the Pioneer Fund wants to keep tilting at that windmill, they can, but the rest of the field is going in a different direction