This chapter presents a summary of the career of Richard M. Lerner within the field that, during his professional life, changed its label from child psychology to developmental science. Lerner summarizes the influence of the scholars and the ideas they championed in shaping the breadth of his career, from his days as a doctoral student at the City University of New York in the late 1960s and early 1970s to the more than a quarter century he spent at Tufts University, where he served as the Bergstrom Chair in Applied Developmental Science and Director of the Institute for Applied Research in Youth Development. Lerner explains how the idea of mutually influential coactions between individuals and contexts (i.e., individual⬄context relations) found its roots in the comparative psychology work of T. C. Schneirla and evolved to become embedded in relational developmental systems-based models that emphasize the dynamic character of human development across the life span.

No form of biological life exists independent of other lives across its ontogeny. Among humans, mutually beneficial and adaptive (functional) development occurs when (1) an individual acts in ways that contribute to the well-being of the person’s social ecology, including the other individuals in the social world and the social institutions of this context, and (2) the social world supports the positive and healthy development of the individual. Within dynamic, relational developmental systems–based models of human development, these dynamic individual ⬄ individual/social institution relationships constitute adaptive developmental regulations and are the essence of prosociality. We present a dynamic model of the links among prosociality, positive youth development (PYD), and character virtue development. We present the theoretical rationale for the hypothesis that the enhancement of character virtue development through specific character education programs can provide the contextual conditions that, when aligned with an individual’s attributes of thriving, increase the likelihood that PYD and prosociality will be linked among youth.

The goal of developmental science is to describe, explain and optimize within-person change and between-people differences in within-person change across the life span (ontogeny) (Lerner, 2018). As such, repeated assessments of individuals across x-axis (temporal) divisions is the sine qua non of the essential features of developmental science research. In other words, to fulfil the goal of developmental science, longitudinal designs are required to obtain evidence contributing to understanding or to enhancing ontogenetic change (Collins, 2006). However, measuring one or more individuals at two or more successive ontogenetic points is a necessary but insufficient basis for developmental longitudinal research.

As is documented by the chapters across this volume, repeated measures must be taken at points of ontogeny for which there is a theoretical basis for expecting these measures (1) to assess changing features of (that is, variational or, ideally, transformational tipping points in) the process of development and/or (2) to constitute optimal ontogenetic points in which to enact interventions to enhance the course of developmental change. As is now understood by increasing numbers of developmental scientists, the development process involves relations between attributes of the individual and features of their tiered social, institutional, physical and cultural ecology, an ecology that changes integratively across history (for example, Bronfenbrenner and Morris, 2006; Elder et al, 2015; Overton, 2015).

Moreover, the developmental relations between an individual and the context are not independent. Contemporary theories of human development which emphasize that individual–context relations are mutually influential, represented most often in the literature as individual↔context relations, are at the cutting-edge of developmental science (Dick and Muller, 2017; Lerner, 2015, 2018). The individual–context relations depicted in these models involve dynamic and systematic relations across time and place (Elder et al, 2015). Dynamic models of human development processes require developmentally oriented longitudinal research to be tested.

The chapters in this volume both reflect and expand the theoretical, methodological and empirical foundations of this relational, dynamic developmental systems approach to using longitudinal methods to describe, explain and optimize the ontogenetic development of diverse global youth. Indeed, the chapters portray the ways in which developmentally oriented longitudinal research is uniquely suited to illuminate the features of both individuals and contexts that must be integratively studied to actualize the health and sustainable development of young people.

In this chapter I will focus primarily on the social group as a context for the individual and stress that this context both influences and is influenced by the individual. My goal is to suggest that this bidirectional relation between the individual and the social context within which the individual is embedded may be a key instance of the plasticity of human processes.

Of course, it is possible to focus initially on the group, and not first on the individual; within this more macroscopic emphasis, one may discuss the group as a system of interacting individuals all of whom possess plastic processes and flexibility in influencing and being influenced by one another. In fact, I have discussed elsewhere the nature of, and relation between, these individual and group foci (R. Lerner, 1979, in press) and it is of use to present here some of the key features of these earlier discussions.

A model of individual–context relations

To summarize these other presentations, it is useful to consider the diagram presented in Figure 2. Employing T. C. Schneirla's (1957) terms, this figure illustrates what I described in Chapter 1 as a probabilistic–epigenetic conception of development; in the figure I use the term maturation (“Mat.”) to represent endogenous organism changes and the term experience (“Exp.”) to denote all stimulative influences acting on the organism over the course of its life span.

The preceding chapters have, in my view, indicated that there is plasticity at each of the levels of analysis I have considered. Often, this plasticity derives from processes at one level of analysis influencing and being influenced by other levels' processes. Thus, key processes at any level may be appropriate targets of intervention as a consequence of this plasticity. And because of embeddedness of one level in another, one can modify processes at one level (e.g., cognitive–behavioral ones) to reach a target at another (e.g., those pertinent to neurotransmitters). Such reciprocity provides a compelling rationale of interdisciplinary research and intervention.

Accordingly, there is reason to be optimistic that in the future lie further paths to understanding how to better actualize humans' potential plasticity. But this optimism must be tempered by the recognition that along these paths lie two problematic sets of issues: First, throughout this book I have reviewed evidence that the organism's “reservoir” of plasticity decreases across life; that is, while plasticity is ubiquitous across life, the domains or band within which plasticity may be evidenced or actualized decrease. Second, there are several theoretical, substantive, and technological problems that must be resolved in order to further the ability of science to enhance human plasticity. These two sets of issues constitute significant limitations on both plasticity per se and knowledge about it. Let us treat each issue separately.

Plasticity as an ever-present but declining phenomenon

An organism's plasticity does not remain at a constant level across its life span.