From their early roots in embryology, parallels are drawn between the major psychological and biological foci of organismic theories. Neural plasticity and concepts of causality in developmental systems are discussed. Because the nature of the developmental process necessitates addressing the nonlinear dynamics of complex systems, it is theorized that causal explanations in neural development, just as is the case with psychological processes, should emphasize the individual's active strivings for self-organization as the major determinant of ontogenesis. Whether or not they cohere to form an integrated self, it is hypothesized that the homeostatic, self-regulatory structures of the mind are the major stabilities in the chaotic dynamics of psychological and neural development. © 1994, Cambridge University Press. All rights reserved.