You can test for both by correlating sibling brain sizes with intelligence.mistermack wrote:An interesting thing about intelligence is that brain size doesn't have much to do with it.
It's the internal setup of the brain that counts, and that is phenomenally complicated.
The brain of Ivan Turgenev, the Russian novelist, was weighed at 2021 gm.
The brain of Anatole France was weighed at only 1017 gm after his death.
Turgenev was a noted novelist, France was a Nobel Prize winning writer, one of the most important in French literature.
Whether they had similar IQs is irrelevant.
Related family members on average would have similar brain wiring, so then you compare intelligence to brain size. I know one of those "racist" scientists I follow did do such a study.