Ecology, cognition, and cultural transmission of Tzeltal Maya medicinal plant knowledge
Casagrande, David Gregory
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The goal of this dissertation is to explain patterns in the distribution of medicinal plant knowledge among the Tzeltal; in particular, why some plants are more likely to be known for their medicinal use than other plants. Methods included botanical collection, structured ethnobotanical surveys, landscape vegetation surveys, discourse analysis and participant observation. The explanatory approach was synthetic, drawing on notions from cultural anthropology, ethnopharmacology, ecology, cognitive science, linguistics, and studies of cultural transmission. Explanatory notions were tested by comparing Tzeltal Maya who have lived in the temperate Chiapas Highlands for many generations with other Tzeltal who have migrated from the Highlands to the lowland tropical rainforest within the last 30 years. Both study populations show patterns in which a few plants are known by every-one, but distribution of knowledge decreases as the diversity of plants increases, and most knowledge is idiosyncratic. The effects of typicality in categorization and discourse account for the few widely known plants. Humoral (hot/cold) classification is highly variable, does not facilitate recall of medicinal uses of plants, and has no significant effect on the distribution of knowledge. Cultural interpretations of plant taste and mor-phology are very important in individual cognitive models, but lose importance at the scale of shared discursive models where social and pragmatic themes also influence the dissemination of knowledge. While humoral classification and cultural interpretations of taste and morphology may be important for expert curers, they do not significantly affect the dissemination of knowledge among novices. Species that are more accessible tend to be used more often, and frequency of use is weakly correlated with knowledge distribu-tion. Emic perception of efficacy is the variable that most accounts for the distribution of knowledge. But social organization, individual cognition, and random processes in cul-tural transmission shape and bias the flow of information, and knowledge about many species that fit emic conceptions of efficacy is not distributed throughout the populations.