Young Kissing Girls

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. 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 34 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. 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.