He's retarded and you still asked him to think? That's insensitive! (sarcasm) I kid, don't cry.


Along similar lines to what linkinwayne stated, different parts of our brain performs different functions. If you mean we don't use our entire brain for rational thoughts, then that's true. And it is because we need it for other functions, such as breathing, emotions and motor functions.

That said, our understanding of the human brain is still extremely limited. It is only in recent times that research into the human brain has seen a spike. Hopefully more of our questions can be answered in the years to come.