a standing kiss in the river...

Anthropologists have not reached a consensus as to whether kissing is a learned or an instinctive behavior. It may be related to grooming behavior also seen between other animals, or arising as a result of mothers premasticating food for their children. Kissing allows prospective mates to smell and taste each other's pheromones for biological compatibility. Women are subconsciously more attracted to men whose major histocompatibility complex portion of their genome is different than her own, leading to offspring with resistance to a greater number of diseases, and thus having a better chance of survival. [1] [2] [3] This explains why couples are more likely to bond if they have the right "chemistry". Many non-human primates also exhibit kissing behavior.[4]