Plant knowledge among Congo Basin hunter-gatherers

Plants have long been central to human life, from early hominins to contemporary hunter-gatherers and industrialised societies. In many communities, they remain a primary source of treatment alongside or in place of Western medicine. Beyond healing, plants serve diverse functions, including hunting and foraging, ritual practices, and the regulation of social norms. This diversity makes plant knowledge a useful domain for examining how cultural traits are transmitted, stabilised and diversified over time. In this paper, I present quantitative and ethnographic data on the use of 33 plant species by over 200 BaYaka hunter-gatherers in the Congo rainforest. I describe patterns of plant use frequency, functional diversity, and agreement among individuals, and situate these patterns through comparisons with other Congo Basin hunter-gatherers and examples from the literature on great ape self-medication. The results reveal substantial variation in how widely different plants are used and in the number of use types attributed to each species. Plants used by a larger proportion of individuals also show higher agreement on their primary function, suggesting stabilisation of particular uses within the population. Some plant uses are shared across human groups and, in a few cases, across species, a pattern often interpreted as consistent with adaptive explanations. Other patterns, however, are more plausibly explained by non-adaptive processes, including cognitive biases that shape how people perceive and reason about plants. The study provides descriptive and comparative evidence relevant to debates in cultural evolution concerning the persistence, diversification and interpretation of ecological knowledge. I conclude by outlining directions for future research that combine quantitative approaches with closer attention to cultural meaning and transmission processes.