How did I not put the pieces together?! HDFS 276

I know I should've noticed these earlier since I've heard about these 'unsymmetrical' body parts before. It was only until recently I put the pieces together...

It's normal for females to have one boob slightly larger than the other (usually left)

It's normal for males to have one testicle/sack larger than the other

Why is this so??? Which part of evolution made it that way and for what purpose?