I'm not a biologist/anthropologist but there is a question that comes up again and again and which I couldn't find any deeper thought, even not a speculation. As far as I understand it, according to modern evolutionary science, the anatomically modern Homo Sapiens Sapiens exists since about 100-300.000 years. Lets be conservative and take 100.000. However, human's ability to build a culture, a society, a civilization that uses the rational mind, an analytic thinking that gives birth to philosophies and, even more recently, to science and technology showed up only very late compared to the human's history. Lets say with the Sumer civilization about 3.000 BC. Now, this implies that, despite having anatomically a fully developed brain, for about 95.000 we were doing not much with our intelligence other than hunting, surviving, develop very rudimentary tools, migrate and not much more but without any cultural development which one should assume is proper of a human brain such as thinking, developing increasingly sophisticated tools, develop philosophies, religions, arts, music, sciences, math, technologies, etc. The latter even not much developed before the scientific and industrial revolution in the last few centuries.
This doesn't make much sense to me. One might argue people were busy with surviving, there was no education and we couldn't develop our IQ, there were no books for cultural transmission, etc. This might be part of the answer explaining a stop of cultural evolution for some centuries, even some thousand years, but for 100.000 Years? This doesn't look to be the fully picture.
So, my question is if there is something (article, book, etc.) of someone who pondered on this aspect in more detail? Is there a possible explanation why evolution produces a brain without using its full capacities for 95% of its existence so far? Are we 100% sure that the brain humans had 50.000 ago are the same we have nowadays?