Culture evolves following a process that is akin to biological evolution, although withsome significant differences. At the same time culture has often a collective good value for human groups. This paper studies culture in an evolutionary perspective, with a focus on the implications of group definition on the coexistence of different cultures.It presents a model of cultural evolution where agents interacts in an artificial environment. The belonging to a specific memetic group is a major factor allowing agents to exploit different niches with, as aresult, the coexistence of different cultures in the same environment.