ABSTRACT
Instructive theories of adaptation hold that the environment imprints its pattern on an otherwise unstructured network, whereas selective theories hold that the environment merely triggers choices between preprogrammed alternatives. Most psychological theories of learning and memory tend to be instructive, but in other domains of biology, such as evolutionary theory and immunology, the trend has been toward selective adaptation. This is reflected also in theories of the development of the visual system and the acquisition of birdsong and human language. The selective action of the environment seems to interact with growth, and is sequentially programmed by growth. This mode of adaptation is well exploited by humans, in particular, because the period of postnatal growth is especially prolonged. It allows for flexible adaptation to particular conditions (e.g., languages, skill demands) drawn from a vast number of potential options, and is “gene-saving” in that genetic programs need only provide the options, with the environment making the choices. I also suggest that the interaction between asymmetrical growth patterns and environmental inputs may program the characteristic functional asymmetries of the human brain.
