I always thought this one could be taken apart on simple common sense grounds. The brain is very "costly" for the human species to maintain, in terms of calorie

I always thought this one could be taken apart on simple common sense grounds. The brain is very "costly" for the human species to maintain, in terms of calories required to run it, and risk during childbirth (amongst other factors, no doubt). Given this, why have it, and leave 90% of it unused? Mr Darwin would give a thumbs down to such a strategy.