I really hate to butt into these arguments but I think you're trying to argue that humans evolved from slime or cave dwellers or whatever you claim we came from into the beings we are today with one of the most complex brains on the planet. How's that efficient?
Efficiency is being as complex as required, and no more. Sometimes highly efficient items are very complex; sometimes they are incredibly simple.
Look at the diesel engine (complex, but efficient at low RPMs), and the ramjet (incredibly siple, but efficient at very high speeds). Both are as complex as required to achieve their goals.