We're not particularly brilliant compared to cave men. The cognitive capacity of the **** sapiens is pretty much static and more or less depends on the size of the brain. That's why even older examples of the **** species would perhaps be able to function if brought up in modern society. They would probably have the mental capacity of a young teenager and evidently even they function (well, mostly).
What really sets us apart from the cavemen is the civilisation and culture we built from those early beginnings. We all stand on the shoulder of giants.
I just think about these Things Things (Our Sun will Die 1 day Earth and the Human Race is sitting on a Time Clock, If You think about the question of what is The Meaning of Life, it's Clear Evolve or Die . . .