Howcome we humans have such a thing called marriage?

How come us human beings have such a thing called marriage? How come other living things in our world don’t have marriage? What makes us different from them? Why do we need it?
Such a simple question and I want to hear your thoughts about it. You can post it in the forums (The link is below) or in this blog. (I’d appreciate it more if you post it in the forums though) =)

This is to help me for my next blog entry

Take me to the forum topic to post my answer