They had the same rough cognitive abilities potential, but isn't it possible that something non-genetic - such as the ability to read and write - plays a signif

They had the same rough cognitive abilities potential, but isn't it possible that something non-genetic - such as the ability to read and write - plays a significant enough part in raising the "total intelligence of a society" that the times before it was common for more than a tiny minority of people to read or write the average effective intelligence really was lower, significantly enough to make "people back then were as smart or dumb as we are" not true? Possibly even on an individual level - that learning to read and write may allow each of us to become more "clever" than if we hadn't. But especially on a societal level, where the ability to read and write has meant that education isn't (as) bottlenecked as when the only learning possible was direct from someone who had learned directly from someone else - even before communication technologies like phones and the internet, the ability to write down scientific research and send it to other non-local researchers sped up a lot of scientific progress. And while people of today may not have an intrinsic better ability of understanding specific things than people of 500 years ago, people in politics do study historical politics (both recent and ancient) to learn from and form new ideas around, so while it's not quite as easy as science to see trees of research where learning/understanding X led to the possibility of also discovering Y, it's surely equally plausible in social subjects that without as much written thinking on the subject, people were also less capable of thinking about it to today's levels? And that's just thinking about reading and writing, the first thing that popped into my mind. Maybe there's lots of other things that had significant effects too? Maybe diet / available food either had a direct impact on cognitive abilities, or had an impact on lowering the average energy people had leading to lower cognitive function? Etc.