Fire, temperature control, and silcrete heat treatment at Diepkloof and Mertenhof Rock Shelters, West Coast, South Africa
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Archer, W., Mackay, A., Porraz, G., Presnyakova, D., Stahlschmidt, M., 2026. Fire, temperature control, and silcrete heat treatment at Diepkloof and Mertenhof Rock Shelters, West Coast, South Africa. Journal of Human Evolution 217, 103853.
Abstract
Transformative technologies that alter raw material properties, rather than just raw material shape and size, are key proxies for the evolution of human cognition and social learning. Silcrete heat treatment in the southern African Middle Stone Age (MSA) is one such proxy. Yet debate now centers not on whether heat treatment occurred in the African MSA but on how it was organized across settings—from controlled insulated setups to embedded hearth-side practices—and how factors such as raw material properties and fire management conditioned those choices. In this study, we argue that archaeological heating-temperature distributions for silcretes provide a proxy for reconstructing fire-use contexts, which in turn allow inference of how heat treatment was organized within broader domestic and social practices. We apply a nondestructive near-infrared protocol—targeting changes in silanol (SiOH) and molecular water (H2O)—to estimate heating temperatures for Howiesons Poort artefacts from Diepkloof and Mertenhof Rock Shelters. As calibration, we use a dataset comprising 225 observations on silcrete flakes heated to prespecified temperatures, which underpins both categorical classification and continuous temperature prediction for the archaeological collection. Heating temperature estimates for the archaeological materials cluster at ∼400–450 °C—an established optimal range for improving silcrete knappability—with smaller numbers of lower and higher values forming expected tails, a pattern that implies intentional fire temperature management by humans. This distribution of temperature estimates is more consistent with lateralized heating adjacent to domestic hearths than with tightly controlled insulated systems. While such a pattern does not uniquely demonstrate embedded heat treatment, it is most parsimoniously explained by routine placement of silcrete within the thermal gradients of domestic fires rather than by the use of segregated, specialized heating systems. We suggest that later MSA groups possessed the capacity for tightly controlled heating but typically met technological goals with minimal organizational overhead, reflecting risk-sensitive choices about time, fuel, and raw material fracture. By showing how a transformative technology was integrated into routine domestic contexts, our results highlight cross-domain cognition and probably low-friction social transmission as key dimensions of later MSA technologies—traits that foreshadow later expansions of complexity in Homo sapiens.
Transformative technologies that alter raw material properties, rather than just raw material shape and size, are key proxies for the evolution of human cognition and social learning. Silcrete heat treatment in the southern African Middle Stone Age (MSA) is one such proxy. Yet debate now centers not on whether heat treatment occurred in the African MSA but on how it was organized across settings—from controlled insulated setups to embedded hearth-side practices—and how factors such as raw material properties and fire management conditioned those choices. In this study, we argue that archaeological heating-temperature distributions for silcretes provide a proxy for reconstructing fire-use contexts, which in turn allow inference of how heat treatment was organized within broader domestic and social practices. We apply a nondestructive near-infrared protocol—targeting changes in silanol (SiOH) and molecular water (H2O)—to estimate heating temperatures for Howiesons Poort artefacts from Diepkloof and Mertenhof Rock Shelters. As calibration, we use a dataset comprising 225 observations on silcrete flakes heated to prespecified temperatures, which underpins both categorical classification and continuous temperature prediction for the archaeological collection. Heating temperature estimates for the archaeological materials cluster at ∼400–450 °C—an established optimal range for improving silcrete knappability—with smaller numbers of lower and higher values forming expected tails, a pattern that implies intentional fire temperature management by humans. This distribution of temperature estimates is more consistent with lateralized heating adjacent to domestic hearths than with tightly controlled insulated systems. While such a pattern does not uniquely demonstrate embedded heat treatment, it is most parsimoniously explained by routine placement of silcrete within the thermal gradients of domestic fires rather than by the use of segregated, specialized heating systems. We suggest that later MSA groups possessed the capacity for tightly controlled heating but typically met technological goals with minimal organizational overhead, reflecting risk-sensitive choices about time, fuel, and raw material fracture. By showing how a transformative technology was integrated into routine domestic contexts, our results highlight cross-domain cognition and probably low-friction social transmission as key dimensions of later MSA technologies—traits that foreshadow later expansions of complexity in Homo sapiens.