Collaboration, the coordination of actions to achieve a common goal, is a ubiquitous human behavior from an early age. Thus far, most research on collaboration has focused on its evolutionary origins, earliest occurrences, and outcomes (e.g. benefits). In this dissertation, I examine potential mechanistic and developmental causes of young children's collaboration in the hope of shining further light on how human collaboration develops and functions. I do so by conducting a detailed interdisciplinary examination of predictors of young children's spontaneous dyadic collaboration. Chapter 1 provides an outline of how this research aims to contribute to developmental research on human collaboration. Chapter 2 examines cognitive predictors, Chapter 3 environmental predictors, and Chapter 4 a physiological predictor of collaboration. Finally, Chapter 5 discusses the significance of the results for future research and important issues on the horizon for researchers to consider. (author abstract)