Exchange (gift exchange) became an important concept in anthropology around 1920, when Malinowski's empirical studies of trade systems among the Trobrianders and Mauss's theoretical work on the gift appeared, almost simultaneously. The theoretical inheritance from Mauss follows three very distinct directions: (1) actor-oriented anthropologists (Barth, Bourdieu), who see exchange as a metaphor of interaction generally; (2) economic anthropologists and historians (Polanyi, Sahlins), who developed theories on precapitalist economic systems; and (3) French structuralism (Lévi-Strauss), which developed theories of kinship based on the exchange of women, and a more general theory of meaning as a product of exchange / contrast.