Well, if you compare any human child with a snail you'll find that the human does almost infinity better at answering questions on IQ tests so we could say it's

Well, if you compare any human child with a snail you'll find that the human does almost infinity better at answering questions on IQ tests so we could say it's all genetic. Or we could take a sample of humans and feed the control group but not the other group over a course of a few weeks and see that environment plays a huge role. But over the range of upbringings we see in the US and genotypes we see in the US it's more genetic than not. But that doesn't mean that that's true across the globe. If some dirt farmer from a place with no iodine in the salt, no folate in the bread, and no access to modern public health, medicine, or schooling comes to the US their kids will tend to have an IQ something like 20 points higher.