[mtgp1000]

You don't have enough information to go from this

>that's only 80 mental mutations between us and the Homo species that made this axe.

To this

>These guys were just about as smart as us.

You don't know how much of an influence any individual mutation could have made. Also there's no reason to suspect more than [or less than] one mutation per generation.

Just look at the range of "gifted" people in our society - mutations which likely enable savants and such. Men like Newton and Da Vinci, if their successes are due to genetic mutations (I suspect to a significant degree this is the case) placed in another time could individually make the difference between a stone and metal age.

Point being, 80 generations of mutation may be enough to drastically change the human mind - especially considering the immense selection pressure for certain kinds of intelligence, which varies with culture and technology (e.g. stone vs metal age).

Edit: I suppose this comes down to how much evolution you believe happens in the form of punctuated equilibria