The author proposes the theory that infants who are superior to the average child in some one respect, as superior strength, will not be advanced in motor development, but that infants suffering from a corresponding deficiency may be retarded. The discussion is orientated primarily toward walking. Three postulates are formulated: (1) there are multiple requirements for the onset of walking, (2) these requirements are not met simultaneously, and (3) these factors are to some degree independent in their development. The deductions are made that the onset of walking (1) can be delayed by postponing the fulfillment of any single factor beyond date of normal walking, and (2) can be induced at a specific date earlier than normal only if all factors involved are moved forward to this date. Ossification and strength, intelligence, sensory handicaps, special practice, and restriction of practice are discussed in relation to the onset of walking.