Newborns start off capable only of simple feelings of pleasure and pain. Through increased experience and cognitive maturation, these sensations are elaborated and refined into various distinct emotions. Just as infants do not know how to run without first learning how to sit, stand and walk, they do not instantaneously develop jealousy in the precise moment when a sibling is initially presented. Jealousy emerges through a gradual, though invisible, developmental process in which infants slowly acquire certain kinds of expectations. Through their experiences with parents, infants come to expect parental attention and they expect it to have certain qualities.
Happy babies expect it to be plentiful, prompt, predictable and tender.
Finally, infants expect parental attention to be exclusive, or at least preferential. The process of emotional development that evolves over a period of years is still not fully understood, but it is clear that a simple form of jealousy is established by the first birthday, even though infants have never met their future siblings and have never witnessed their parents attending to another child. If an infant does not express jealousy and has not been exposed to a jealousy-inducing event, do not assume that jealousy is nonexistent in that infant. If parents wish to know the status of their infant s jealousy development, they do not need to await the day they confront him with his newborn baby sister or brother. All they have to do is set up a situation that triggers jealousy by violating their infants expectations of receiving preferential treatment.