On why Wayne Dennis found Hopi infants retarded in age at onset of walking.

Dennis (1940) found Hopi infants were slower in onset of walking whether or not the cradleboard was used, than infants from other socioethnic groups. This investigation supplemented a repetition of the interview procedure used by Dennis with questions concerning circumstances of Hopi life infants, who were discovered to begin walking at a mean age of 12.5 mo., were advanced by 2.5 mo. over the date of walking recorded by Dennis. Infants reared on the cradleboard, like those studied by Dennis, walked as early as unrestrained infants. Differences in genetic background, physical health, and nutritional status between the earlier time and the present day which could account for the delayed onset of walking noted by Dennis were evaluated. Former inadequacy of the infants' diet seemed to be the most significant of the possible underlying conditions. The accelerated date of walking at present may reflect the enhanced quality of Hopi infant nutrition brought about by external programs for food supplement, particularly the Indian Women, Infants and Children's program.