From a primitive naïve and simple character, Harlequin evolves into a smart, more sophisticated one, that with his simplicity outwits all the arrogant and greedy personages with whom he interacts.
And the evolution (and decadence) is well marked by the changes in its mask, his stage "persona", which goes from an almost savage and Zanni-like appearance to the witty and ironic guy we mostly remember. His character was definitely a success as changes in the Italian Comedy were surely determined by the public's acceptance of gags and characters, and due to the partially improvised script, changed from day to day, I speculate.
The evolution of the character went on until the 18th century, when it became too sophisticated, no more wit, the hunger and fantasy gone.
And the Commedia dell'Arte is going towards its end.