What advance in capabilities?
Other than intelligence, humans are remarkable in:
1) Manual dexterity - unless compared to other primates.
2) Color vision
3) extreme endurance in a patheticaly slow run
None of which seems to me to require the hardware capabilities that make Einstein and Mozart possible.
Granted, binocular color vision requires some rather major signal processing capabilities. But not enough to explain a brain that big. And what does that signal processing buy you in the wild? Particularly when driven by relatively weak eyes and ineffective predatory capabilities. A human without tools is a lousy enough predator that binocular vision is an almost complete waste. Prey that is slow enough and close enough that you or I can kill it without tools we can find with one eye. We'd get lots more milage, as predators, out of better fingernails.
Actualy, there is one raw survival capability that a big brain could give a non-tool-user: orienteering. A smart critter can go places - and get back - better than one that is only able to outsmart a yam and realize a large predator is trouble. But there are lots of ways to develope that capability without going to the trouble of a brain size large enough to commonly kill a mother in the birth process.
No, I'm pretty sure that our species has big brains for, well, politics. That they are also good for arts and sciences is a happy accident.
