but it seems we have developed a brain with a capacity that is far greater then our needs.
You think so?
You don't
need to have the intelligence that you have?
Then you would be happy, I guess, to spend a month or so
not making the smartest decisions you can think of, but much dumber ones? You'd get on just fine that way?
OK then, try it. Every time you have a choice to make, and your smart human brain tells you what you ought to do, ignore it and do what a monkey would do instead. Try this for a month and let us know how you get on.
And then you will maybe realize that such intelligence as you have is in fact a selective advantage and not a biological superfluity.