When the mood strikes, a kiss can catch us in a mix of tastes, textures, mysteries—and scents.  We kiss nervously, flirtingly, angrily, or excitedly.  And a kiss is not just all about sex: Hollywood celebs throw us air kisses, mobsters impart the kiss of death, and an astronaut kisses the soil after a safe return home.  So why, then, are we so taken with the kiss?

Scientists agree our lips evolved first for eating—and then later for speech.  Yet, with a kiss, a different kind of ‘hunger’ applies.  Kisses set off a whirlwind of neuro-chemical messages yielding anything from sensations of touch to sexual arousal; feelings of closeness to even a wave of euphoria.

However, kissing is not a solo affair, and kissing transmits external messages as well.  The bringing together of two bodies sets off messages just as powerful with your partner (whether they are precisely the same feelings is another matter altogether).  Kisses pack quite a punch: even one can transmit much information about the potential of a relationship.  Research proves that kisses are so powerful that a ‘first kiss’ gone badly can derail even the most promising of relationships.

Scientists believe that lip-locking evolved as a means to promote mate-selection.  Kisses transmit olfactory, tactile and postural types of information tapping into both the conscious and unconscious mind that drives decisions, including a genetically-compatible mate!  Some researchers believe that a kiss can even disclose the extent to which a partner might commit to raising children—central to our specie’s survival.

Nearly 50 years ago, British zoologist and author Desmond Morris posited that kissing probably evolved from primates: mothers chew food for their young, and then feed them mouth-to-mouth.  And since chimps still feed this way, early man probably did so, as well. 

This press of outturned lips against lips may have later progressed as a way to comfort children in times of hunger—and eventually becoming a general expression of affection.  (Leave it to us humans to take these first parental kisses down the myriad of paths we have today!)

It is believed that unseen chemical messengers named pheromones helped along the evolution of the intimate kiss.  Both animals and plants use pheromones to communicate: insects, for example, emit pheromones to signal alarms, point out a food trail or announce sexual attraction.

In 1995, a Swiss researcher showed why pheromones are so important in humans, too.  He had women sniff t-shirts worn by men, and asked which smelled best.  The results were startling: the women did not choose randomly, which was discovered by comparing the DNA of the women and men.  Instead, women overwhelmingly picked the scent of man whose histocompatibility complex (MHC)—the genes that forge our immune systems—differed from their own.  (Different MHC’s mean less immune overlap, and the increased likelihood of healthy, disease-resistant kids.)  Thus, kissing may be a woman’s way of assessing a potential mate’s immune compatibility—without investing an excessive amount of time, energy in (and not to mention sexual activity with) a man.

However, these scientists aren’t telling the average person anything new: when it comes time to close your eyes and lean in, we all know that a kiss is never just a kiss.