Chapter 5. Complex cognition required for compound adhesive manufacture in the Middle Stone Age implies symbolic capacity
Compound adhesives were made in the Middle Stone Age (MSA) of southern Africa using a complex process in order to attach stone tools to shafts. Glue-makers must switch attention between fire control, measuring ingredients, and assembling compound tools. No rehearsals or recipes guarantee success; artisans must multi-task (a characteristic of modern human minds involving cognitive fluidity) and think abstractly about properties of glue ingredients. Mental rotation, an ability implying advanced working memory capacity, is needed to place stone inserts in various positions to create novel weapons and tools. The manufacturing process is sufficiently intricate that the early artisans must have had minds with abilities that overlapped those of people living today; such minds are capable of symbolic thought and action.