To assess claims about developmental homologies, or devologies, longitudinal data are needed. Here, we illustrate this with the debate about the purported foundational role of neonatal imitation in children's social and cognitive development. Cross-sectional studies over the past 35 years have clarified neither the prevalence of imitation in newborns nor its relationships to later developing skills. Thus, scholars have been able to maintain diametrically opposing explanations of neonatal imitation in the literature. Here, we discuss this issue and outline how large-scale longitudinal approaches promise to resolve such debates and have the potential to use individual difference measures to uncover links to later development. © 2011 Wiley Periodicals, Inc. Dev Psychobiol 55: 52–58, 2013.