Biology and evolution

Anthropologists have not reached a conclusion as to whether kissing is learned or a behavior from instinct. 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 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 from their own, leading to offspring with resistance to a greater number of diseases due to heterosis, and thus having a better chance of survival.

Non-human primates also exhibit kissing behavior. Dogs, cats, birds and other animals display licking and grooming behavior among themselves, but also towards humans or other species. This is sometimes interpreted by observers as a type of kissing.

The physiology of kissing

Kissing is a complex behavior that requires significant muscular coordination; a total of thirty-four facial muscles and 112 postural muscles are used during a kiss. The most important muscle involved is the orbicularis oris muscle, which is used to pucker the lips and informally known as the kissing muscle.Fact: date=August 2008 In the case of the French kiss, the tongue is also an important part. Lips have many nerve endings so they are sensitive to touch and bite.

Disease transmission

Diseases which may be transmitted through kissing include mononucleosis and herpes, when the infectious virus is present in saliva. Research indicates that contraction of HIV via kissing is extremely unlikely, although a woman has been infected with HIV by kissing in 1997; both the woman and infected man had gum disease (so transmission was through the man's blood, not saliva).

Kissing in Western culture

In modern Western culture, kissing is most commonly an expression of affection. Between people of close acquaintance, a reciprocal kiss often is offered as a greeting or farewell. This kind of kiss is typically made by brief contact of puckered lips to the skin of the cheek or no contact at all, and merely performed in the air near the cheek with the cheeks touching. People may kiss children on the forehead to comfort them or the cheek to show affection, and vice versa.