As the decade of the 1980s ended, the view of developmental science that Paul Mussen (1970) had forwarded at the beginning of the 1970s—that the field placed its emphasis on explanations of the process of development—was both validated and extended. Mussen alerted developmentalists to the burgeoning interest not in structure, function, or content per se but to change, to the processes through which change occurs, and thus to the means through which structures transform and functions evolve over the course of human life. His vision of and for the field presaged what emerged in the 1990s to be at the cutting edge of contemporary developmental theory: a focus on the process through which the individual's engagement with his or her context constitutes the basic process of human development.
The interest that had emerged by the end of the 1980s in understanding the dynamic relation between individual and context was, during the 1990s, brought to a more abstract level, one concerned with understanding the character of the integration of the levels of organization comprising the context, or bioecology, of human development (Lerner, 1998a, 1998b). This concern was represented by reciprocal or dynamic conceptions of process and by the elaboration of theoretical models that were not tied necessarily to a particular content domain but rather were focused on understanding the broader developmental system within which all dimensions of individual development emerged (e.g., Brandtstädter, 1998; Bronfenbrenner, 2001; Bronfenbrenner & Morris, 1998; Ford & Lerner, 1992; Gottlieb, 1997; Magnusson, 1999a, 1999b; Sameroff, 1983; Thelen & Smith, 1994, 1998). In other words, although particular empirical issues or substantive foci (e.g., motor development, the self, psychological complexity, or concept formation) lent themselves readily as exemplary sample cases of the processes depicted in a given theory (Lerner, 1998a), the theoretical models that were forwarded within the 1990s were superor-dinately concerned with elucidating the character of the individual-context (relational, integrative) developmental systems (Lerner, 1998b).
During the 1980s and 1990s similar concerns with understanding the nature of the integration between individual development and cultural context led to the development of sociocultural perspectives on human development. As already noted, some scholars extended Vygotsky's (1978) socio-historical theory to emphasize the study of human development as it is constituted in sociocultural context (Cole, 1990, 1996; Rogoff, 1990;Wertsch, 1985,1995). Othersconceptual-ized culture as the meaning systems, symbols, activities, and practices through which people interpret experience (Bruner, 1990; Goodnow, Miller, & Kessel, 1995; Greenfield & Cocking, 1994; Markus & Kitayama, 1991; Shweder, 1990).
By the end of the twentieth century, then, the conceptually split, mechanistic, and atomistic views, which had been involved in so much of the history of concepts and theories of human development, had been replaced by theoretical models that stressed relationism and integration across all the distinct but fused levels of organization involved in human life. This dynamic synthesis of multiple levels of analysis is a perspective having its roots in systems theories of biological development (Cairns, 1998; Gottlieb, 1992; Kuo, 1976; Novikoff, 1945a, 1945b; Schneirla, 1957; von Bertalanffy, 1933); in addition, as noted by Cairns (1998), the interest in understanding person-context relations within an integrative, or systems, perspective has a rich history within the study of human development.
For example, James Mark Baldwin (1897) expressed interest in studying development in context, and thus in understanding integrated, multilevel, and hence interdisciplinary scholarship (Cairns, 1998). These interests were shared as well by Lightner Witmer, the founder in 1896 of the first psychological clinic in the United States (Cairns, 1998; Lerner, 1977). Moreover, Cairns describes the conception of developmental processes—as involving reciprocal interaction, bidirectionality, plasticity, and biobehavioral organization (all quite modern emphases)—as integral in the thinking of the founders of the field of human development. For instance, Wilhelm Stern (1914; see Kreppner, 1994) stressed the holism that is associated with a developmental systems perspective about these features of developmental processes. In addition, other contributors to the foundations and early progress of the field of human development (e.g., John Dewey, 1916; Kurt Lewin, 1935, 1954; and even John B. Watson, 1928) stressed the importance of linking child development research with application and child advocacy—a theme of very contemporary relevance (Lerner, Fisher, & Weinberg, 2000a, 2000b; Zigler, 1999).
The field of human development has in a sense come full circle in the course of a century. From the beginning of the last century to the beginning of the present one, the history of developmental psychology has been marked by an increasing interest in the role of history—of temporal changes in the familial, social, and cultural contexts of life—in shaping the quality of the trajectories of change that individuals traverse across their life spans. As a consequence of incorporating into its causal schemas about ontogenetic change a nonreductionistic and a synthetic conception about (as compared to a Cartesian split view of) the influence of context— of culture and history—the field of human development has altered its essential ontology. The relational view of being that now predominates in the field has required epistemolog-ical revisions in the field as well. Qualitative as well as quantitative understanding has been legitimated as scholars have sought an integrated understanding of the multiple levels of organization comprising the ecology of human development. In fact, relational perspectives embracing the developmental system stress the methodological importance of triangulation across quantitative and qualitative appraisals of multilevel developmental phenomena (Lerner, Chaudhuri, & Dowling, in press).
In essence, then, as we pursue our scholarship about human development at this early part of a new century, we do so with an orientation to the human life span that is characterized by (a) integrated, relational models of human life, perspectives synthesizing biological-through-physical ecological influences on human development in nonreductionis-tic manners; (b) a broad array of qualitative and quantitative methodologies requisite for attaining knowledge about these fused, biopsychoecological relations; (c) a growing appreciation of the importance of the cultural and historical influences on the quality and trajectory of human development across the course of life; and (d) a synthesis of basic and applied developmental science.
These four defining themes in the study of human development are represented in contemporary developmental systems theories, perspectives that constitute the overarching conceptual frames of modern scholarship in the study of human development. We believe as well that across the rest of this century the field will advance through the coordinated emphasis on a culturally and historically sensitive science that triangulates quantitative and qualitative appraisals of the relations among the multiple levels of organization fused within the developmental system.
In short, there has been a history of visionary scholars interested in exploring the use of ideas associated with developmental systems theory for understanding the basic process of human development and for applying this knowledge within the actual contexts of people to enhance their paths across life. For instance, scholars building on Vygotsky's (1978) sociohistorical perspective have explored promising conceptual frameworks to explicate the integration between the individual and cultural context in the process of development (Cole, 1996; Wertsch, 1995). Accordingly, the chapters in this volume reflect and extend the diverse theoretical perspectives that emphasize understanding dynamic and integrated developmental processes as they are situated in the varying contexts of people's lives and circumstances.
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