I happened across a crime blotter from Philadelphia in the 1830s. Wouldn't you know it, the majority of the criminals in Philadelphia then happened to be of the same demographic as the criminals in Philadelphia today. You can't fool Mother Nature. It is sort of a family tradition, passed down through the generations. It's in their DNA.
We would all agree that some genetics traits do cause lower IQ, but that agreement appears to be limited to an extra chromosome.
Any other genetics that might affect intelligence seem to be off limit for serious discussion.