In combat, the heart is on the left, which would be kept away from the enemy.
But I'm sure there were right handed people before there were advanced piercing weapons.
Our process of thought could have been more logical in progression, stimulating the right side of the body as the left side of the brain took up reasoning.
The North star is in the North, and is sacred through many cultures, and using that as a fixed point across the globe, the sun would rise on the right, or East, and would be associated with life, setting in the west, or left, or death.
In the womb, what organs surround the uterus, and would they cramp the left side in standard infant position?
I'm left handed, so I can't tell what benefits there are in being right handed aside from writing, in a non-determined possibility.
Hope that helps.