Looking for the monoliths? Jokes aside, probably not much. Biological classifications don't imply sameness. You don't get anatomically modern humans until 30,000-50,000 years ago. Even that doesn't tell you much about cognitive ability. Think about something like the Flynn Effect [1]. In the past century real IQ scores rose by more than a standard deviation throughout most of the world. That means a person of perfectly mean intelligence today would be more intelligent, so far as IQ can measure, than 84% of people from a century ago. And over thousands of years? Of course now the Flynn Effect seems to have reversed in most developed nations with us becoming literally less intelligent, again so far as IQ can measure.
The point is that even in a time frame of a single century you're looking at very radical changes in intellectual ability between populations that would appear, on the surface, to be practically 100% identical. When you start talking about tens of thousands of years ago, it's impossible to do even begin to intelligently speculate based on anything other than achievement. And what did we achieve? As you mention, not much. And so the only justifiable explanation is that we probably didn't have that much going on upstairs until relatively recently.
I think the most interesting question is a direct spin off of yours. What triggered the intellectual spike? Was it in any way related to whatever caused the more contemporary spikes in intelligence? Why are IQs now decreasing and can global intellect fade away as rapidly as it emerged? Probably the most depressing possible solution to the Fermi paradox!
[1] - https://en.wikipedia.org/wiki/Flynn_effect