How normal is variable, or how variable is normal?

Variability is an important property of the central nervous system, and it shows characteristic changes during infancy and childhood. The large amount of variations in the performance of sensomotor functions in infancy is called indiscriminate or primary variability. During toddling age the child develops the capacity to select adaptive variations, and then automatize them: secondary or adaptive variability. The latter is required for the development of motor skills during later preschool age and school age. The question 'How normal is variable or how variable is normal is a wrong question, as any form of variability must be interpreted according to its extent, type and age adequacy.