Cultural and cognitive mnemonics of hot versus cold classification in Tzeltal Maya medicinal plant knowledge

Explanations for the ubiquity of hot versus cold (humoral) plant classification throughout Latin America remain elusive. I interviewed 28 Tzeltal Maya to verify a medicinal plant domain using consensus analysis and test hypotheses that humoral classification is a cognitive mnemonic (facilitating recall of plant use) or a cultural mnemonic (facilitating cultural transmission of knowledge). Consensus about medicinal plant use was high, but interviewees were uncertain about humoral classification, contradicted their own classifications on 41% of occasions, and tended to recall a plant’s medicinal use before its humoral property. Agreement about humoral classification was not correlated with knowledge about medicinal use (r_s = 0.10, P > 0.50). Medicinal uses of many plants were well known despite little agreement about the plants' humoral properties. Humoral classification is probably not a cognitive or cultural mnemonic for the Tzeltal. It likely results from semantic extension and may symbolically legitimize the knowledge system.