There is plenty of evidence for this (such as a 30 point increase in IQ among Poles over a couple generations). Culture and education matter in innumerable ways when it comes to cultivation and expression of intelligence. The irony about racists like this OP is that they are invariably the most stupid people around.
A lot of that had to do with the Germans and Russians exterminating the smartest Poles during WWII. They had nowhere to go but up.