The hypothesis was that these Functions would appear, approximately in the order listed , and in any case with the 'informative' significantly last; that in Phase I, they would be separate from one another, with each expression (and therefore each utterance) having just one function ; and that the mastery of all of them with the possible exception of the last-would be both a necessary and a sufficient condition for the transition to the adult system. It is conceivable that these functions determine the initial development of language in all cultures ; if so this would have major implications for our understanding of the evolution of language.