By Three Months

• The first display of emotion that we see in babies is the social smile. This starts at between six to ten weeks of age. Unlike the earlier smile, which most mothers recognize to be a sign that the baby is passing gas, the social smile is the baby's attempt to respond to whoever has spoken to the baby. It develops because the baby has watched his parents smiling and has discovered that that expression works to please others and to gain positive attention from the other people in the room.
  
  

By Four Months

• By four months a baby can laugh out loud, as well as produce other sounds to show pleasure. Laughter is an emotional expression, as well as an indication that the baby understands when something is funny. As "The Encyclopedia of Childhood and Adolescence" explains, the baby "recognizes incongruity." As with smiling, babies start experimenting with laughter because the people around them model it.
  
  

By Five to Nine Months

• By five months the baby knows how to respond to friendly voices by smiling and cooing. By nine months she responds when someone whom she knows addresses her by name. All of these early displays of emotion --- smiling, cooing, laughing, and greeting people she knows --- are examples of learned behavior. The development of a baby's emotions comes through socialization, usually in response to her parents.
  
  

By Seven to Twelve Months

• Expressions of negative emotions develop later in babies. They begin to express fear, disgust, and anger at between seven to twelve months. At the same time they may develop separation anxiety, and they will cry or protest when they are left with a caregiver other than their mother or father. Even when a baby is too young to articulate what is driving his emotional display, adults can read the sign to understand his behavior.
  
  

By Twelve Months

• In addition to developing emotions because of having been socialized or because of anger, fear, or disgust, babies learn to reflect their mother's emotions. This is known as social referencing. When the mother feels uneasy, anxious, afraid, or upset, the baby can sense this and may express similar emotions. Gradually, the baby learns to show her own emotions so that by the time she is twelve months old, she can initiate her own loving expressions.