Proposes a broader approach to research in human development that focuses on the progressive accommodation, throughout the life span, between the growing human organism and the changing environments in which it actually lives and grows. The latter include not only the immediate settings containing the developing person but also the larger social contexts, both formal and informal, in which these settings are embedded. In terms of method, the approach emphasizes the use of rigorously designed experiments, both naturalistic and contrived, beginning in the early stages of the research process. The changing relation between person and environment is conceived in systems terms. These systems properties are set forth in a series of propositions, each illustrated by concrete research examples.(1� p ref)(PsycINFO Database Record (c) 2016 APA, all rights reserved)