We develop the vital bond of attachment between a mother and her child through a smiling response. As a visual stimulus, the smile has attained its unique configuration principally by the simple act of turning up the corners of the mouth. The mouth is opened to some extent and the lips pulled back, as in the expression of fear, but with the curling- up of the corners, the character of the expression of radically changed. This development has in turn led to the possibility of another and contrasting facial posture"that of the down-turned mouth. By adopting a mouth line that is the complete opposite of the smile it is possible to signal an anti-smile. Just as laughing, 50 also the unfriendly face has evolved by a pendulum swing from the friendly face.

But there is more to smiling than a 'line of the mouth. As adults, we may be able to convey our mood by a mere twist of the lips, but the infant throws much more into the battle. When smiling at full intensity, it also kicks and waves its arms about, stretches its hands out towards the stimulus and moves them about, produces babbling sounds, tilts back its head and protrudes its chin, leans its trunk forward or rolls it to one side and exaggerates its respiration. Its eyes become brighter and may close slightly; wrinkles appear underneath or along the eye and sometimes also on the bridge of the nose; the fold of the skin between the sides of the nose and the side of the mouth becomes more accentuated, and the tongue may be slightly protruded. The body movements seem to indicate a struggle on the infant's part to make contact with the mother. With its clumsy physique, the baby is probably showing us all that remains of the ancestral private clinging response.