ABSTRACT
The onset of independent locomotion marks a major transition in the ontogenetic development of the human infant just as the assumption of bipedal locomotion marks a major transition in the phylogenetic development of the species. The course of early motor development, from neonatal reflexive behavior through upright, unaided locomotion, has been glanced over too casually by child development researchers. Independent bipedal locomotion, along with expressive language and functional tool use, distinguish Man from most other species, and an understanding of the onset of these attributes ontogenetically is likely to provide important clues about the development of the human infant generally. This development encompasses a change from a nonverbal, relatively fearless, crawling infant that mouths and bangs objects indiscriminately to a young person who talks, fears strangers and strange places, walks upright, and uses the objects of his culture appropriately. Zelazo (1982a) and Zelazo and Leonard (1983) have argued that these developmental changes during the first year reflect a profound cognitive metamorphosis that accounts for a variety of new capabilities ranging from gross and fine motor to linguistic, social, and cognitive abilities.
