Introduction

In writing about behavioural phenotypes, we can see just how far the field has come in only a few short years. In the first edition of this volume, published in 1999, we began our chapter with the paradox that geneticists had discovered over 750 different genetic disorders associated with intellectual disabilities (ID), but that behavioural work lagged far behind. We lamented the so-called ‘two cultures’ of behavioural work in ID (Hodapp & Dykens, 1994), noting how researchers who were more biomedically oriented versus more behaviourally oriented rarely intersected one with another.

But much has changed over the past five to ten years. Consider the sheer number of research articles on behaviours of the most prominent genetic disorders of ID. Using computer searches comparing the 1980s to the 1990s, one sees remarkable, almost exponential, increases. From the 1980s to the 1990s, the numbers of behavioural research articles on Williams syndrome increased from ten to 81; on Prader–Willi syndrome from 24 to 86; on fragile X syndrome from 60 to 149. Even in Down syndrome, the sole aetiology featuring a longstanding tradition of behavioural research, the amount of behavioural research almost doubled — from 607 to 1140 articles — over these two decades. The years since 2000 have shown even more pronounced increases, particularly with regards to Williams and Prader–Willi syndromes.

Granted, such progress is uneven, with many more studies performed on Down syndrome than on almost all other syndromes combined.

The late 20th century is a challenging period for those concerned about development and developmental approaches to pathological populations. On the one hand, influential workers in the field of developmental psychology are questioning the very foundations of the discipline itself (Bronfenbrenner, Kessel, Kessen, & White, 1986). They question whether progressive development (i.e., change that leads to a specified end point) can be documented in any or all domains, and, if so, whether developmental progressions hold across all children in all contexts. Similarly, these workers raise issues about whether achievements are universal or are specific to one culture, and note that many changes that occur during childhood seem regressive in nature (e.g., Bever, 1982). All of these concerns, voiced by major figures in developmental psychology, throw into disarray long-held views about the very nature of human development.

On the other hand, there is a broad movement toward the developmental camp, as many people working with different groups purportedly employ “developmentally based” approaches. In the mental retardation (MR) field, we note the ubiquity of group homes, leisure-activity training, and even behavior-modification programs that are supposedly based on the principles of normal development. The term “development” here implies that the program promotes positive change over time or better adaptation to the environment. Given the imprecision in terminology, it is understandable that those who do not consider themselves to be developmentally oriented (e.g., Switzky, Rotatori, Miller, & Freagon, 1979) decry the use of the term at all.

The contributors to this book were asked to perform a difficult task – to specify what has come to be known as the developmental approach to mental retardation. They were asked to delineate what general developmental theory, findings, and perspectives tell us about retarded development, and what mental retardation research tells us about general developmental processes. The hope is that by joining findings from these two areas we can gain a clearer understanding of both normal development and mental retardation.

The construction of a comprehensive developmental approach to mental retardation is difficult to accomplish because it encompasses two topics that many consider to be incompatible. On the one hand, developmental theorists have typically considered only nonhandicapped persons when discussing the nature of developmental processes. Even in debates concerning individual differences and the universality of development, little attention has been paid to the development of mentally retarded persons. Similarly, debates about sequences, structures, and environments have also been conducted without regard to evidence from retarded populations (see Inhelder, 1968, and Woodward, 1979, for notable exceptions).

On the other hand, researchers of mental retardation have had little use for general developmental theory. Mentally retarded persons have traditionally been viewed as different from other persons in that they suffer from one or a few specific defects; their functioning has therefore been judged to be incompatible with traditional developmental theory.

Workers interested in children's behavior have long disagreed about the idea that there is one, fixed, and invariant sequence of development in any particular domain. On the one hand, workers such as Piaget (1954), Kohlberg (1969), and Slobin (1970) and Lenneberg (1967) have argued that there are invariant sequences in cognition, morality, and language, respectively. From observations of children from one culture or a small set of cultures, these workers have asserted that their particular sequences of development constitute the single orderings of achievements that lead to more adaptive and higher-level functioning. Some have even argued that the search for so-called universals in development is the true mission of the developmental psychologist.

On the other hand, the quest for universals has been derided as simplistic by certain workers interested in cross-cultural (Shweder, 1984) and atypical (Switzsky, Rotatori, Miller, & Freagon, 1979) development. These workers have asserted that there are many roads to the same end point, that development is variable and individualized across children. For example, behaviorists argue that environmental conditions should be able to guide change in a number of directions – that is, in the appropriate rearing environment, any particular child could be made into “a doctor, lawyer, artist, merchant-chief and yes, even into a beggar-man and thief” (Watson, 1926, p. 10). Other workers have emphasized that the speed of development is strongly influenced by the environment (Hunt, 1980), and even that developmental sequences and end points differ from one culture to another (Miller, 1986).

The timing of a book is a curious thing. Sometimes the book appears as a herald to a field, the first inkling that a new theory or new approach has arrived. It points the way, outlines the territory, and energizes workers who may be interested but not quite know how to proceed. Or a book may serve as a capstone to a discipline, the last word (and work) of an overmature area.

More often, however, books appear in a middle position, somewhere between the beginning and the ending of research in an area. Books of this sort attempt to make explicit or to redirect theoretical and empirical efforts, explaining what the authors do for the benefit of other workers in the field. These workers, in turn, usually have some sense of the growing enterprise, but desire to know more, to understand the limits and tensions, the ways in which the particular theory or new approach fits in or contrasts with more widely accepted approaches.

Although we are not certain that all will agree, we envision this volume as a book of the middle variety – an explication, reexamination, and elaboration of an area that has existed for some time. Granted, a hardy band of developmentally oriented workers has for 20 plus years pursued issues such as similar sequences and structures in retarded individuals, the two-group approach, and motivational–personality functioning in retarded individuals.