And William H. Calvin makes the opposite case - that of intelligence being an adaptive response to extreme climate changes - in his book A Brain for All Seasons.
And Matt Ridley makes an interesting supposition in Nature via Nurture that early Homo (ie, erectus) might have used the famous hand axes as a way of showing off their intelligence to females as much as, if not more than, actually butchering meat. I don’t think it was actually his idea, but someone else’s that he was quoting.
Is intelligence still being selected for??!? I think the fact that Chris Matthews exists should be enough to answer that question. 
(sorry, so sorry)