Is kissing a universal expression of affection?

Actually, kissing isn't a universal expression of affection. It is possible that it's learned behaviour. It's been proposed that kissing was learned from Indian culture, where the earliest record of kissing has been found. Through military conquests, kissing was spread to the middle east and then rome and greece. The romans loved their kisses and helped make it popular. But even then, kissing wasn't always a sign of affection, but rather respect or subservience.

There are cultures where kissing is not used to show love or affection. Eskimo people rub their noses together! Is it a coincidence that these people are traditionally very isolated?

Also, as my own opinion; I wonder if kissing is more a sign of trust than of any emotions. You're in close proximity to eachother, eyes closed, and exchanging all of these chemical messages (in your saliva, scent, sweat). It's just the perfect way to engage all of your senses!