Seems like a pretty strange custom. when did it start and why.
Well, earliest reference I can think of off the top of my head is Judas and Jesus so it goes back to at least ca. 33 CE.
there have to be some references in the old testament also. I wish i could think of some off of the top of my head.
I’m pretty sure kissing dates back to prehistoric times, which makes it impossible to establish an exact origin. Anthropologist Desmond Morris speculated that kissing began as a way for mothers to pass pre-chewed food (in the days before Gerber) to their young children. Morris makes interesting guesses from time to time, but bear in mind that there isn’t a lot of evidence for this.
That doesn’t sound like a really good way to pass food to a baby. I mean why not just use their hands, its not like they where birds.
First of all, Judas’ kiss was likely on the cheek, which I doubt is the kind of kiss the OP is referring to.
Second of all Indian sources at least that old (first century CE) describe the kind of kissing referred to in the OP (and other fun pastimes). Indians have always been good at sex–that’s why there are 1 billion of us now. 
With regards to the actual OP: the lips have more nerves of than any other region on the face, I believe. This affords us good control over the lip/mouth muscles (which is why we can speak well), and also means they have a lot of sensation. We wouldn’t kiss if it didn’t feel good, and it feels good because we have a lot of sensation there. We’d bonk heads to show affection if it felt better than kissing.
This was going to be my answer to the OP as well. I can recall learning of this in a college anthropology class. It seems a logical explanation to me.
As for theendisnear’s comment:
Uh, the important adjective you missed is “pre-chewed.” So the mom should chew the food, spit it out into her hand, and then give it to the baby?
I would also submit that a poster who doesn’t know how to spell “were” presents pretty good evidence that the end is indeed near.
Yeah that was exactly the way i figured they would do it, spitting the food on your hand and then hand feeding the baby seems alot more practical than spitting it right in their mouth. And sorry about any typos, english isn’t my first language.
No, not if you need one of your hands to hold the baby and the other to feed yourself; don’t forget that we’re talking about a primitive situation, not silver service on polished dinner tables.
Besides, there are cultures where this is still done; it’s quite practical.
I apologize for my intemperate comment. Regrettably, there seem to be large numbers of American-born individuals for whom English might as well be a foreign language, too!
[QUOTE]
*Originally posted by BigStar303 *
You know, BigStar, it wasn’t that theendisnear didn’t know how to spell “were”, but that he used “where” in the wrong context. If you’re going to be nitpicky, at least pick the right nit.
I didn’t think that any mammals out their pre-chewed their food. Once they get off of moms milk don’t they switch to getting thier own. What animals do this? And don’t give me any of that platapuss duckbill crap I mean a real mammal.
I know dogs regurgitate their food, and here’s the cite to back it up:
http://www.peteducation.com/whypet/licking.htm
“Dogs lick for a number of reasons. They lick to groom themselves and others. Mothers lick their puppies to clean them and stimulate their urination and defecation. Older puppies and the young of wild canids (relatives of the dog such as wolves) lick the mouths of the adults as a greeting to stimulate them to regurgitate. The puppies eat this regurgitated food as they are weaned from their mother and begin to eat solid food. As the puppies grow older, the licking becomes a way of welcoming others back into the pack and increasing the bonds between the pack members.”
Are dogs a real enough mammal for ya? 
Interestingly (I’ve tried this) children between eight and eighteen months will try to kiss you (with their mouths wide open) if they see you chewing right in front of their faces.
Besides dogs, as mentioned by D18, wild canids such as wolves and African Wild Dogs feed the pups by regurgitation between the time they have ceased nursing and when they can actually start eating fresh meat.
At the Toronto Zoo one day Little Miss D18, D18 Jr., and I had the pleasure of seeing the big gorillas puking on the ground and the little gorillas eating it up. Mercifully, Mrs. D18 remained at home to write report cards.
Does this happen in the wild, or is it one of those things that only happens in captivity?
I’ve read a few historical novels set in various Asian locales that stated or implied that kissing was a western innovation only introduced to Asia in the past few hundred years. Normally, I don’t rely on novels as research tools, but as these books weren’t “yellow peril” types and seemed otherwise well-researched, it caused me to think. Any cultural differences on kissing?
Sua
http://www.wsu.edu:8001/vcwsu/commons/topics/culture/behaviors/kissing/kissing-essay.html#top
Talks about the premastication theory and another about the “Sharing of souls”.
Pretty interesting reading.
Any mother will tell you that nursing stops immediately, as soon as the little one has his or her first tooth. You need more than one tooth for most adult foods. Hence, a transition period.
Are we talking full-contact mouth-to-mouth tongue-wrestling exchange-of-bodily-fluids type of kissing or the more decorous peck on the cheek?
Not that I really know, but it just strikes me that the origin of these two modes could be quite different.