Navajo infants who spend many hours a day strapped to a cradle board are as advanced in motor development as infants who are not confined in this way. Which of the following is the newest interpretation of this finding?
◦ Motor development is guided only by genetics and maturation and is unaffected by experience.
◦ Navajo parents spend a lot of time interacting with their infants when they are removed from the cradle board.
◦ The cradle board confines full-body action, but not arm and head motion. Navajo infants engage in as much upper body exercise as other infants.
◦ Navajo infants are precocious in motor development. Even with delays caused by the cradle board, they are as advanced as other infants.