Kissing may have many different names - snog, pash, smooch, making out and the romantic 'pull' - but it reduces down to one simple, intimate act.
Here, this video explains that it is 'instinctual learned behaviour' that is around 3,500 years old. Around 90% of the world's cultures engage in kissing (which leaves us wondering what the hell the other 10% do).
As for why most people remember their first kiss, it's because kissing creates a 'drug-like blend' of endorphins including oxytocin, dopamine and serotonin.
Apart from the obvious, kissing also helps figure out who you want as a mate. Apparently, women can tell how much testosterone a guy has because 'kissing transmits sensory signals on a sub-conscious level.'