Whereas in the previous chapters the emphasis has been primarily on the endogenous factors that influence infant mental state awareness, in the subsequent chapters I will examine in detail the exogenous influences on the infant's developing sense of people. As discussed earlier, social interactionist theorists put much emphasis on the social factors that influence infants' awareness of people (Bowlby, 1969; Bruner, 1973; Fogel, 1993; Stern, 1985; Trevarthen, 1979; Tronick 2004; Vygotsky, 1978). These authors can be divided into two groups, each differing in the emphasis they put on either the exogenous or endogenous factors when explaining how infants develop the concept of people. Those with a nativist or constraint–constructivist orientation postulate that infants begin life with an awareness of their own emotional states. They emphasize the social origins of the self and the infants' innate sense of people. Trevarthen (1979), for instance, maintains that infants have innate capacities to act on the social and physical environments and are instrumental in their own cognitive development. He explains that infant behaviors such as cooing (present in neonates), smiling (appears within minutes after birth), pre-speech movements of the mouth and tongue, eye movements, and attempts to communicate point to the social nature of babies.