Plasticity is a concept whose significance in developmental scholarship waxes and wanes, as the past decades of this century bear witness. For example, the term was a major entry in the 1902 edition of J. M. Baldwin and E. P. Poulton's Dictionary of Philosophy and Psychology. It was defined as “that property of living substance or of an organism whereby it alters its form under changed conditions of life” (Vol. 2, p. 302). At that time and under the recent influence of Darwinian thought, the discussion of plasticity focused on its origins and role in evolution. In the thirties and forties, plasticity (or modifiability) was again a center of attention. There was Lashley's conception of brain plasticity as well as the early-childhood studies of the detrimental impact of environmental deprivation and, correspondingly, the possible benefits of compensatory programs.

The 1970s and 1980s have seen renewed interest in the notion of plasticity. Research, rather than being restricted to childhood, is now being done, for example, in psychological gerontology, where it has been found that aging is not a fixed general process of decline, but rather that the older organism retains considerable potential for variability and plasticity. Similarly, in continuation of Lashley's earlier ideas, groundbreaking work is now being done in developmental psychobiology (e.g., Gollin, 1981) that underscores the need to study and articulate models that explicitly focus on variations in development.