The universal smile

E. O. Wilson tells us here how smiling is a universal physiological character:

"Within the face the mouth is the principal instrument of visual communication. The smile in particualr is a rich site of secondary epigenetic rules. Psychologists and anthropologists have discovered substantial degrees of similar programmed development in the uses of smiling across cultures. The expression is first displayed by infants between the ages of two and four months. It invariably attracts an abundance of affection from attending adults. Environment has little influence on the maturation of smiling. The infants of the !Kung, a hunter-gatherer people of South Africa's Kalahari desert, are nurtured under vey different conditions from those in America and Europe. [...] Yet their smile is identical in form to that of American and European infants, appears at the same time, and serves the same social function. Smiling also appears on schedule in deaf-blind children and even in thalidomide-deformed children who are not only deaf and blind but also crippled so badly they cannot touch their own faces."

E. O. Wilson, Consilience, From genes to culture.