I would disagree about “humans” having little differentiation from ordinary apes. This is an assumption that is made about what “science” has found. We are truly arrogant if we think that we can study fossilized bones and tell how smart the person was, the color of their skin, how hairy they were, etc. The Bible is clear that God created man in HIS IMAGE. Not in the image of an ape,kangaroo, lizard, fish, or one cell organism (all in our family tree based on the teaching of evolution at different times.)
Ancient man was very intelligent. I would suggest reading the book “The Puzzle of Ancient Man” by Dr. Donald Chittick
It would have to depend on how far back you go. According to the current evidence, “man” was pretty intelligent even as far back as 1million years ago. The med flood happened 5 million years ago, at a point when the available evidence doesn’t even show tool use.