From the Cover: Implications for complex cognition from the hafting of tools with compound adhesives in the Middle Stone Age, South Africa

Abstract

Compound adhesives made from red ochre mixed with plant gum were used in the Middle Stone Age (MSA), South Africa. Replications reported here suggest that early artisans did not merely color their glues red; they deliberately effected physical transformations involving chemical changes from acidic to less acidic pH, dehydration of the adhesive near wood fires, and changes to mechanical workability and electrostatic forces. Some of the steps required for making compound adhesive seem impossible without multitasking and abstract thought. This ability suggests overlap between the cognitive abilities of modern people and people in the MSA. Our multidisciplinary analysis provides a new way to recognize complex cognition in the MSA without necessarily invoking the concept of symbolism.

Fig. 1.

Stone tools (segments) with adhesive from Sibudu Cave. (A) Segment with red ochre visible to the naked eye on that part of the tool that would have been in a haft (i). Microscopic views of red ochre and plant gum on the tool (ii and iii). (B) Segment with black fat on that part of the tool that would have been in a haft (i). Microscopic views of fat on the tool (ii–iv).

Fig. 2.

Particle size analysis of ochre samples used in our experiments. Fe₂O₃ is synthetic hematite.

Fig. 3.

Comparison of ZP readings on red ochre no. 15, A. karroo gum, and yellow ochre no. 10. Ag, Acacia gum; ro, red ochre; yo, yellow ochre. Samples in Ai and Bi were mixed with 50 mL of d-water; samples in Aii and Bii were mixed with 50 mL of 0.05 M KCl. The gray shaded blocks show the pH and ZP at which maximum adhesion might be expected to occur.