Europa writes:
3. Why do we have a brain so big? I don't remember how much of the brain we use, but it is a pretty small percent.
This is not true, we use pretty much all of our brain, just not at the same time.
I'll leave the other two for other people to answer.
Oh, and a free tip, use the "peek" button on the bottom right of this post to see how I did that nice little quotebox.