The introduction of shyness in infants

Infants at say one year old, become able to monitor adults’ emotional attitudes toward them as well—a kind of social referencing of others’ attitudes to the self. 

This new understanding of how others feel about their selves opens up the possibility for the development of shyness, self-consciousness, and a sense of self-esteem.... Evidence for this is the fact that within a few months after the social-cognitive revolution, at the first birthday, infants begin showing the first signs of shyness and coyness in front of other persons and mirrors.

As Tomasello goes on to discuss, once the infant understands other individuals as intentional beings and herself as one participant among others in a social interaction, then whole new cognitive dimensions arise. The child comes to be able to participate in “joint attentional scenes”—social interactions in which the child and the adult jointly attend to some third thing, , for an extended period of time, and in which the child can conceptualize her own role from the same “outside” perspective as the other person. Joint attentional scenes in turn provide the framework for the acquisition of language and other kinds of communicative conventions.