So I'm assuming you read my post in Dec 2009 on why we have 2 kidneys? The real question is why certain organs are oriented on 1 side? Like why is the gall bladder on the left or right side and why is the heart mainly on the left side? And why do the left hemisphere of the brain handle certain functions?
Link: why-we-have-2-kidneys (or 1 windpipe & 2 lungs)