Kissing, as any pre-adolescent human will tell you with one “yuck,” appears to be one of the oddest of all the odd behaviors in which our species indulges. What would make two sane, healthy people expose themselves to each other’s germs so willingly?

Turns out, there is a kiss for just about any emotion, including hate, envy, deceit and greed. Google Judas Iscariot. There was a fellow from whom you would not want so much as a peck on the cheek. Then we have that most mixed of messages conveyed by the air kiss, a slight turn of the head and a smack in mid-air near the cheek. The hostess gets the point.

But for most of us, assuming that our childhood revulsion of all things icky is over, kissing is about as fine a pastime as can be enjoyed by two warm-blooded animals. We’ve been at it for a long time, at least since 1500 BC when kissing is first talked about in early Vedic scriptures. Scientists still aren’t sure whether sucking face is a learned or innately human gesture. An evidential case can be made for both. Many animals appear to be kissing. The “Kissing Gourami” is so named for the obvious reason that it will pucker up like nobody’s business. Thing is, only the males do it, and they aren’t stuck on each other. A fight for territory is likely to ensue, and the behavior is so stressful that sometimes the fish getting kissed immediately drops dead from fright. Talk about passive aggressive.

But as far as we can tell, only humans and Bonobo apes mean reproductive business when kissing. One theory is that the kiss evolved from mothers’ pre-masticating food for infants. Another holds that the male’s saliva becomes full of testosterone when aroused and the female can “taste” it and will encourage the specimen with which she would like her genes to mingle. Otherwise, it’s some version of the dreaded handshake instead of a kiss.

Putting aside all variations of the place-your-lips-on-my-posterior type of kiss, for the last 800 years or so since dentistry has solved the halitosis issue, we look for every opportunity to plant one. A recent study even revealed that people who kissed their partners before leaving for work live longer, get into fewer accidents and earn more money than those who don’t. So pucker up! It’s good for your heart and your wallet.

For clips of smooches in lick-your-lips High Definition, click here.