A central concern for Durkheim was the question of how certain societies maintain internal stability and survive over time. He proposed that such societies tend to be segmented, with equivalent parts held together by shared values, common symbols or (as his nephew Marcel Mauss held), systems of exchanges. Durkheim used the term "mechanical solidarity" to refer to these types of "social bonds, based on common sentiments and shared moral values, that are strong among members of pre-industrial societies". In modern, complex societies, members perform very different tasks, resulting in a strong interdependence. Based on the metaphor above of an organism in which many parts function together to sustain the whole, Durkheim argued that complex societies are held together by "solidarity", i.e. "social bonds, based on specialization and interdependence, that are strong among members of industrial societies".