The mountain stream of infant development

Development is complex. It encompasses interacting domains, at multiple levels, across nested time scales. Embracing the complexity of development—while addressing the challenges inherent to studying infants—requires researchers to make tough decisions about what to study, why, how, where, and when. My own view is inspired by a developmental systems approach, and echoed in Esther Thelen's (2005) mountain stream metaphor. Like a river that carves its course, the active infant navigates the social and physical environment and generates rich inputs that propel learning and development. Drawing from my experiences, I offer some recommendations to guide research on infants. I encourage researchers to embrace discovery science; to observe infants in ecologically valid settings; to recognize the active and adaptive nature of infant behavior; to break down silos and consider the nonobvious; and to adopt full transparency in all aspects of research. I draw on cascading influences in infant play, language, and motor domains to illustrate the value of a bottom-up, cross-domain, collaborative approach.