 Moreover, he discovered that average measures of the cranial size of children born within ten years of their mothers' arrival were significantly different from those of children born more than ten years after their mothers' arrival.Boas did not deny that physical features such as height or cranial size were inherited; he did, however, argue that the environment has an influence on these features, which is expressed through change over time.This work was central to his influential argument that differences between races were not immutable.