Abstract
Archaeological indicators of cognitive complexity become increasingly prevalent during the African Middle Stone Age, with the habitual exploitation of red ochre widely viewed as a key feature of the emergence of modern human behaviour. Given that some of the uses of ochre remain ambiguous, we present the preliminary results of an ongoing study in which we explore the efficacy of red ochre as a photoprotective device or sunscreen. The capacity of ochre to inhibit the susceptibility of humans to the detrimental effects of ultraviolet radiation was confirmed through the in vitro calculation of the sun protection factor values of samples derived from the Kunene Region in Namibia and the Bokkeveld Group deposits, Western Cape Province, South Africa. Visible spectroscopy was employed to determine colourimetric parameters of samples and assess the correlation between ochre colour and sun protection factor. The possible role of ochre as a sunscreen agent for hominin populations, including modern humans, during the Middle Stone Age in Africa is explored. We conclude that the habitual use of red ochre as a photoprotective agent likely played a role in the ability of prehistoric humans to adapt to novel environmental circumstances.
Highlights
Environmental variables have been shown to exert a substantial influence on ecosystems, communities and populations.[1,2] Of the various climate-driven selective pressures that operated during the evolutionary history of Homo sapiens in Africa, negotiating the risks and benefits of persistent exposure to sunlight presented an enduring challenge
When compared by processing method, samples processed by Ovahimba women had the highest mean sun protection factor (SPF) (8.9±1.2), those experimentally ground directly onto a grindstone had a mean SPF of 6.2±2.4 and those ground using the method employed by Ovahimba women had a mean SPF of 3.4±0.8
It is possible that the habitual exploitation of ochre during the Middle Stone Age (MSA) reflects some form of cultural adaptation to rapidly changing environmental circumstances
Summary
Environmental variables have been shown to exert a substantial influence on ecosystems, communities and populations.[1,2] Of the various climate-driven selective pressures that operated during the evolutionary history of Homo sapiens in Africa, negotiating the risks and benefits of persistent exposure to sunlight presented an enduring challenge. Shortwave UVC (280–200 nm) is potentially the most dangerous type of UV radiation (UVR) for humans, but is largely absorbed by the ozone layer.[4]. Sunlight is an essential environmental factor in most ecosystems and the beneficial effects of moderate exposure to sunlight are well known.[5] Positive correlations exist between adequate UVR exposure, vitamin D synthesis, calcium absorption and human fertility.[6] Vitamin D (1.25 dihydroxyvitamin D3) in turn reduces the incidence of rheumatoid arthritis, coronary heart disease, diabetes, multiple sclerosis, osteomalacia, rickets, schizophrenia, autoimmune diseases and several types of cancer.[7] excessive UVR exposure can lead to malignant skin diseases including cancer and mitochondrial (mtDNA) and nuclear (nDNA) molecule damage.[8,9]
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