Religion. Ever hear about any new Civilization that did not have any religion? Religion provided people with the basis for a rule of law . It got people to work together rather than fight each other.
I’d guess that the person of median-intelligence now is intellectually inferior to the median European cave dweller of tens of thousands of years ago. My rationale for this is that stupid people have it a lot easier these days. There are all sorts of social safety nets in place keeping the dim and dull alive and reproducing and voting Democrat. Back in the day, folks had to get by on their wits, and if you weren’t very bright, your chances of surviving were diminished.
#4 democrat types over the eons kept interfering with progress. Truly.