It is suggested that the extra chromosome in Down's syndrome (DS) results in a generalized decrease in canalization of development. Three palatal dimensions - height, width and anteroposterior length - were measured in moreal twins and in DS subjects. Twin analyses showed that the relative contribution of environmental factors to variability was greatest for palatal length. Of the three dimensions, palatal length was the most abmoreal in DS. Similarly, the maximum atd angle, which is more susceptible to environmental variation than the finger-tip ridge count, is much more deviant from the normal in DS. In both systems the less-stable trait in moreal populations in norm abnormal in DS. These data are consistent with a generalized amplified instability of development in DS.