Open Discussion: Sibling Rivalry

A few days ago, a close friend and I were discussing sibling rivalry.   Where does is stem from?  How is it learned?  In both our families, and hopefully most others, it certainly isn't taught.  And if it isn't widely taught, why is it clearly visible no matter where you travel in the world?  Certainly children crave attention and strive to get noticed by mom and dad, but I find that the majority of arguments in our family have nothing to do with my getting my attention.  At a younger age, I'm sure the egocentric mind plays a major role in sibling rivalry. "I" am the most important person and therefore, "I" should always get my way.  Young minds simply cannot comprehend any differently.  But as the children grow, so does the rivalry.  I know without a doubt that my girls and my friends' girls love each other 100%, but they can go at it like they are enemies.  For a parent, this can be stressful and irritating.  But unfortunately, sibling rivalry is here to stay.  Where do you think sibling rivalry stems from?  What are your thoughts on controlling it?  Grab a latte, put up your feet, and join the discussion!