A nonzero-sum three-person coalition game is presented to study the evolution of complexity and diversity in cooperation, where the population dynamics of players with strategies is given according to their scores in the iterated game and mutations. Two types of differentiation emerge initially: a biased one to classes and a temporal one to change their roles for coalition. Rules to change the hands are self-organized in a society through evolution. The coevolution of diversity and complexity of strategies and interactions (or communications) are found at later stages of the simulation. Relevance of our results to the biological society is briefly discussed.