Why do we kiss?

I found this article interesting: http://scienceline.org/2006/10/ask-fiore-kiss/

Why DO humans kiss? I've actually thought about that before. I mean sure, its fun and feels good, but what's the real purpose of it? Its kind of odd when you think about it. You press your lips against another person's. You shove your toungues in each other's mouths. But WHY?

This article brings up a good point about it probably being learned or instinctual. Sure, some animal mommies mouth feed their young and continue pressing their lips on the young one, but that's the mom. How often do you enjoy kissing your mom? Its more duty than anything. And human mommies don't mouth feed babies, at least I would hope not haha.

I guess for now I'll take the theory that we kiss to find a mate. It kind of makes sense. No one really wants to date a person really horrible at making out. But why did we choose kissing? Why not judge our mates on their hand shake? I judge people (not necessarily mates) on their hand shakes haha. C'mon science! I want anwsers!