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.ochre ͉ replications ͉ glue ͉ modern behavior ͉ Ͼ70,000 years ago A rchaeologists often use symbolic material culture as a marker of modern behavior, but few agree on definitions of either term or explore the types of mental architecture required for symbolic innovations. Here, we move away from the contentious issue of symbolism and draw on the combined expertise of cognitive and earth scientists to create a fresh way of recognizing, in the deep past, cognitive abilities that overlap with our own. People today have a capacity for novel, sustained multilevel operations; this ability may have arisen from neural connectivity in part of the prefrontal cortex (1). The capacity may be recognizable in some technologies, and we use compound adhesive manufacture as our example. To demonstrate complex cognition, we must show that some executive steps required for compound adhesive manufacture are not possible without mental abilities of the kind implied in the ninth subsystem of the Barnard et al. (2) model of mental architecture. Here, abstract meanings and sophisticated organization of action sequences determine decision making. An earlier eighth subsystem would have been mentally incapable of processing 2 levels of meaning simultaneously or of generating fully abstract concepts about behavior.The use of simple (1-component) adhesives is ancient; for example, birch-bark tar was found on 2 flakes from Ϸ200,000 years (200 ka) ago at a site in Italy (3). At Ϸ40 ka, bitumen was found on stone tools in Syria (4), and a similarly aged site in Kenya yielded tools with red ochre stains that imply the use of multicomponent glue (5). Traces of even earlier (Ϸ70 ka) compound adhesives occur, together with microfractures consistent with hafting, on Middle Stone Age (MSA) stone tools from Sibudu Cave, South Africa (see SI Text and Table S1). Several recipes are evident: sometimes plant gum and red ochre (natural iron oxide-hematite-Fe 2 O 3 ) traces (Fig. 1) occur on tool portions that were once inserted in hafts (6-10). Other tools have brown plant gums and black or white fat, but no ochre ( Fig. 1 and SI Text).We acknowledge the possibility that people at Sibudu colored some of their weapons symbolically, perhaps to signify the blood of prey, but we do n...

Hafted spears and the archaeology of mind

“…For Wadley et al (5), A consists of stone artifacts excavated from the Middle Stone Age site of Sibudu in southern Africa, which are about 70,000 years old. The heart of the inference is the argument B that takes us from features of A to the probable or necessary presence of C, in this case spears with hafted points.…”

“…13 and 14), and still others apply theories of embodied cognition (15). Indeed, Wadley et al (5) themselves tap into a cognitive model of working memory in their argument for mental rotation (16). In the face of competing cognitive models, how does one judge?…”

“…But just what is required, in a cognitive sense, to be able to haft a point to a shaft? In this issue of PNAS, Wadley et al (5) set out to answer this question by duplicating one such hafting technology, identifying the procedures and knowledge required, and arguing that abstract reasoning was an essential prerequisite. In doing so they provide a good example of a relatively new perspective in paleoanthropology-that of cognitive archaeology.…”

Use of red ochre by early Neandertals

“…More "mundane" or "domestic" uses of red ochre (derived from hematite, Fe 2 O 3 ) are known from the ethnographic record of modern hunter-gatherers, for instance, as (internal and external) medication, as a food preservative, in tanning of hides, and as insect repellent (3)(4)(5)(6)(7)(8)(9). Archeological studies have identified ochre powder as an ingredient in the manufacture of compound adhesives (10). Thus, the use of iron oxides for "symbolic" purposes should be viewed as a hypothesis that needs to be tested, rather than simply assumed.…”

Are there alternative adaptive strategies to human pro-sociality? The role of collaborative morality in the emergence of personality variation and autistic traits

“…Notable and novel technological innovations first appear in southernmost region of south Africa at a time of environmental variability after 100,000 years ago for example. These include the heat treatment of flint to improve knapping precision (Brown et al 2009), new standardised and precise project point technology (Shea 2006), microlithic and compound technology (Brown et al 2012), complex adhesives demanding an understanding of chemical reactions (Wadley, Hodgskiss, and Grant 2009), and poisons (d 'Errico et al 2012). Novel precise and standardised beadworking, interpreted as evidence of large-scale networks, appears in northernmost Africa at around 80,000 years ago (Bouzouggar et al 2007).…”