Drawing the line

So much of everything we do is fueled by our perceived need to protect and defend that which we "alone" have planted on this earth.  It's what wakes us in the middle of the night, it's what we worry about, it's what we fight wars over...

Even the charming thank-you card a friend sent me -- a drawing of some wild grass growing near the artist's home -- had these words on the back: "I don't pull out the wild things except in extremis.  I theorize that there should be room for all of us.  I let everything grow until something that I have planted is being choked out -- then even the natives will be pulled!"

When and how do we draw the line between "mine" and "ours"?