ABSTRACT
DR. ETHELYN H. KLATSKIN, my associate at Yale, suggested that the essential idea with which to introduce this subject should be the impossibility of any discussion, except theoretical, of any average development in the United States, for three reasons. The first was the variation over the country as a whole, with its many differences in climate and population groups. For instance, it has been suggested that in the south-west, relatively less clothing and less bundling up in the winter, and greater space for family living, may be conducive to earlier gross motor development, with earlier standing and walking.
