This chapter reviews evidence for fixed sequences of behavioral and psycho-logical development drawing on cross-cultural and cross-population studies throughout the world, and relates these behavioral data to brain development in infants and children. Based on these data, a model is proposed to account for certain universais of psychological behavioral development in infancy in terms of maturing brain function. The chapter draws on data derived from several of these assessment methods including tests of neurological maturation, motor development and social development. Experimental animal studies also demonstrate correlations between myelination sequences and other indices of regional brain development. Neonatal neurological and behavioral assessment scales have produced a detailed characterization of human neurological status at birth. A useful paradigmatic case is provided by the emergence of bipedal locomo-tion, a species typical, centrally organized neuromotor action pattern shown by all normal adults—indeed by all normal 2 year olds—in people species.