The role of causal knowledge in the evolution of traditional technology.

Humans occupy a wider range of environments, process more energy, and have greater biomass than any other species because we are able to culturally evolve complex, locally adaptive technologies. Competing models make different predictions about the role of causal knowledge in this process. Some argue that innovation and transmission cannot occur without causal understanding, while others posit that complex technologies can evolve without causal understanding. Prior research on this topic has been restricted to theoretical work and experimental studies with student participants. The Hadza are foragers who rely on bows for subsistence. We interviewed skilled Hadza bowyers (bow-makers) and compared their beliefs regarding the tradeoffs in bow construction to those revealed by experimental and engineering research. If bowyers understand the tradeoffs, it is plausible that cultural evolution is rooted in causal understanding, while if they do not, the cultural accumulation of knowledge is likely more important in the process. We show that Hadza bowyers understand some mechanical trade-offs but not others, and therefore the evolution of a complex, highly adaptive technology is possible with incomplete causal knowledge regarding key mechanical trade-offs. Instead, some important design choices made by subjects seem to reflect cultural norms. Although previously published reports have suggested that some individuals are recognized by the Hadza as being especially skilled or knowledgeable, our results do not indicate that some individuals are significantly more knowledgeable about bow-making than others, nor is there statistical evidence that causal knowledge increases with age.