intelligence is like 80% genetic, 20% environment.
Caucasians differ in intelligence even though they're close, group wise. Whites, Arabs and Jews all live in different environments and cultures so while their limits may be closely related their IQ will differ because of environment and culture.
People in Africa can have pretty low average IQ scores but when put into America they have an average IQ of I don't know honestly, I think I remember it being around 85? Which makes sense I think, African Americans all have some caucasian in them and they're in a better environment, some of their ghetto black environments are a problem though and as it gets fixed they probably move up to like 90.
I'd safely bet that American caucasian IQ scores are smaller compared to other times too.
IQ is mostly genetic but an environmental change is significant, those 20% can move 100 to 80 or 120
