> It's obviously both genetic and environmental. You can limit people with a detrimental environment (extreme example - inflicting brain damage) but cant improve them beyond their their natural ceiling.

The question besides the obvious is how close to their ceiling the average human is (or even the 90th percentile). Because the entire discourse about “ceiling” implies that people are somewhat limited by their ceiling. But if 90% of the people are plateauing at 30% of their ceiling because of environmental factors, it makes little sense to talk about the ceiling at all.

Given the Flynn effect ended in the 90s in several countries, I'd say the western world is close to it.