An anticipatory smile doesn't reflect just any emotion; it reflects a positive emotion. And somewhat amazingly, a baby's level of anticipatory smiling—her interest in sharing positive experiences—seems to predict her future social behavior. A longitudinal study published last year measured anticipatory smiling in a group of infants at several points throughout their early childhood. Remarkably, levels of anticipatory smiling at 9 months of age successfully predicted social expressivity and competence—essentially, the ability and inclination to engage with other people—at 30 months, almost two years later.
Looked at from this perspective, the experience of smiling prepares us to participate in society. As Messinger has written, "Affecting and being affected by the positive emotional expression of the parent may lead infants to experience the happiness of others as essential to their own happiness." It's a powerful, moving idea, and as I considered it, I reframed how I thought about Isaiah's smiles. He might not be smiling because he was happy. He might be smiling because I was happy. And, in due time, that just might make him happy, too.