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Babies Smile and Behave - 1

Human beings, both adults and children, laugh or smile. What is laugh? That can be the behavior to shrink facial muscles in a complex manner, reflecting one's emotions. People let out their voice and laugh; sometimes they simply smile quietly.

Looking at the natural world, it seems that smiling is observed, among all the mammals, only in human beings with highly advanced emotional functions. Monkeys, though, show a response similar to laughing when they are tickled.

All Babies Laugh by 3 to 4 Months Old

How does ontogeny1 or development of smiling work? About half of healthy babies start to smile by six weeks old; all the babies smile before they become three to four months old.

It is reported, however, that one out of 100 babies who are one week old or younger smiles after being suckled or when going asleep. The behavior, though, is non-elicited smile; it is simply a change of facial expression with shrinking facial muscles and not a smile with emotions responding to an external stimulus. However, this change does not appear when the baby does not feel comfortable.

Smile of newborns is called a social smile with emotions responding to a stimulus; it is a meaningful behavior from the socio-biological perspective. This communication tool causes unique sympathy among adults surrounding babies.

Is smiling a simple facial expression of emotions like happiness or joy in the brain? There is an idea that human beings control necessary blood flow in their brain as well as build up their expressions with their facial muscles.

What Causes Babies' Smile

Babies smile in response to various stimuli. When touched lovingly here and there, to their lips for instance, or talked to, babies smile or laugh.

Generally speaking there is no unique feature to when babies are talked to, but laughing or smiling response is an exception. It is even said that smiling is the only response babies make when they are talked to. As they get older, they laugh or smile more frequently to visual stimuli like expressive motions of faces.

Therefore babies laugh most lively when adults move their faces while talking to them. Any parent has an experience when they play a peek-a-boo, that his or her baby makes a laughing response with the whole body.


1: Ontogeny is all the processes of the development of an individual organism from a fertilized egg (or a parthenogenesis, asexual bud or spore), especially referred to the generation of multi-cellular organism. In this context this means when and how smiling behavior appears and changes.

Kobayashi, Noboru (1981). "Akachan wa waratte kodo suru - 1." (written in Japanese). Tokyo: Child Research Net. Retrieved Oct 9, 2003, from the World Wide Web http://www.crn.or.jp/LIBRARY/KOBY/MIRAI/cbs0105.html
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