If you account for differences in genetics and upbringing, then brain size has a correlation with intelligence. But it's only slight and other factors seem to b

If you account for differences in genetics and upbringing, then brain size has a correlation with intelligence. But it's only slight and other factors seem to be more predictive, like genetics and upbringing. Also it has not been established if bigger brains results in higher intelligence, or that higher intelligence results in a bigger brain. Although nobody fully can explain why the Flynn effect occurs, we do know that there is no single cause, and it's therefor not possible for an increase in brain size to explain the Flynn effect.