I'm a lefty but I do everything but write with my right hand. It's weird because my right hand is the hand I throw with and I do everything the same way a right handed person does. I just write with my left hand and that's pretty much all I use it for.
I saw this article somewhere that was saying why most people are right handed.
They still haven't figured it out yet, but there's a myth saying that soldiers back in time had to hold the sword with their right hand, and the shield with their left hand, so that they could cover their heart that's on the left side.
It is amazing that I can write well using my left and right hand. I write with my left hand when writing on a board and use the right when writing down on papers but I sign with my left hand. I confused whether I am a left or right handed person!