Pretty much all human cultures have kissing, and a few other animals do it as well. But why? Why are we cramming our mouths together? Why don't we nuzzle noses or tap kneecaps? Why don't we butt rub?
Researchers at the University of Leeds have hypothesized that kissing evolved as a way for women to expose themselves to an infection called cytomegalovirus. Never heard of it? Maybe you've heard of its family -- herpesviruses (we're not missing a space between "herpes" and "viruses" -- that's the actual name of the family). The thing about this particular virus is that, much like a Looney Tunes tramp stamp, you don't know if your partner has it until it's too late. By then you've already exposed yourself to something you'll never shake.
And that's bad news for the species -- if a woman develops the active cytomegalovirus while pregnant, there's a 50 percent chance she won't carry the baby to term. But, if she gets exposed in incremental bits in the months leading up to her pregnancy, she can be inoculated from a full-on primary infection. Think of it this way: The virus is kind of like early 2000s boy band music. In small doses, it's not so bad. In large doses, it will abort your baby.
You can see where we're going with this -- the easiest way to transmit the virus is through swapping saliva. The theory is that, rather than moving straight into intercourse (which could immediately get a woman pregnant while giving her mega-herpes and maybe killing her unborn child), females created this courtship-slash-inoculation period -- the kissing season. Which is a way better and less gross theory than the first draft -- that kissing evolved as a natural result of mothers prechewing food for their young (and lovers).
Read about the other 4 reasons why we have sex here on cracked.com.
The following article is from http://cracked.com.