Canalization refers to the frequently observed robustness of mature phenotypes against minor genetic or environmental perturbations during development, as in the example of compensatory growth (Flatt, 2005; Schmalhausen, 1949; Tanner, 1963; Waddington, 1942). G×E interactions have been proposed as one path by which canalization may occur. For example, genetic determinants of plasticity in response to the environment may constrain structures to develop along a heritable trajectory from an undifferentiated beginning to a genetically determined mature state (Garlick, 2002). Repetitive patterns of activity may also sculpt plastic developing structures. An example of this was described by Zelditch, Lundrigan, and Garland (2004), who found that variance in murine skull morphometry decreased during early postnatal development. They hypothesized that high initial variance decreased as initial unorganized immature patterns of motor activity took on the predictable characteristics of adulthood. Such a process is reminiscent of those thought to underlie activity-dependent changes in the cerebral cortex.
