A complex adaptive system may be essential for cumulative modifications in tool design

The cumulative modification of tool designs over time is a crucial development for technological evolution. Cognitive-related prerequisites for this technological capability are innovative behaviour and the faithful inter-generational transmission and maintenance of tool designs by accurate social learning processes. Here, we investigated the hypothesis that a complex of morphological and behavioural adaptations specifically for tool skills is also required. In a novel analysis we compared the tool-associated adaptive patterns in Homo erectus and the New Caledonian crow. Both species provide the most convincing early Homo and nonhuman evidence, respectively, for the making of cumulatively modified tools. We identified probable shared traits in H. erectus and the New Caledonian crow that include morphological adaptations specifically for enhanced tool manipulation and a significant component of daily diet from hunting and/or processing animal food with tools. We propose that a tool-using lifestyle based on animal food that confers a reproductive advantage and evolves enhanced tool manipulation skills, together with appropriate innovative ability and social learning processes, may be essential for cumulative modification of tool designs.