Abstract
The Middle to Later Stone Age transition marks a major change in how Late Pleistocene African populations produced and used stone tool kits, but is manifest in various ways, places and times across the continent. Alongside changing patterns of raw material use and decreasing artefact sizes, changes in artefact types are commonly employed to differentiate Middle Stone Age (MSA) and Later Stone Age (LSA) assemblages. The current paper employs a quantitative analytical framework based upon the use of neural networks to examine changing constellations of technologies between MSA and LSA assemblages from eastern Africa. Network ensembles were trained to differentiate LSA assemblages from Marine Isotope Stage 3&4 MSA and Marine Isotope Stage 5 MSA assemblages based upon the presence or absence of 16 technologies. Simulations were used to extract significant indicator and contra-indicator technologies for each assemblage class. The trained network ensembles classified over 94% of assemblages correctly, and identified 7 key technologies that significantly distinguish between assemblage classes. These results clarify both temporal changes within the MSA and differences between MSA and LSA assemblages in eastern Africa.
Highlights
The transition from the Middle Stone Age (MSA) to Later Stone Age (LSA) signals a major shift in the lithic assemblages produced by African Homo sapiens populations, but this transition occurs over a considerable period, is manifest in numerous ways, and occurs asynchronously in different regions of the continent
In order to engage with the largest number of MSA and LSA assemblages reported from eastern Africa, we focus on patterns of the presence and absence of stone artefact technologies reported from chronometrically dated sites in the literature
Whilst it is clear that some MSA elements persist beyond MIS2, it is generally considered that the main transitional phase occurs in MIS3, and the data were limited to MIS2-5 to enable analysis of changes both within the MSA and between broadly contemporary MSA and LSA assemblages
Summary
The transition from the Middle Stone Age (MSA) to Later Stone Age (LSA) signals a major shift in the lithic assemblages produced by African Homo sapiens populations, but this transition occurs over a considerable period, is manifest in numerous ways, and occurs asynchronously in different regions of the continent. The analyses reported below attempt to shift the debate from one focussed on individual artefact types towards the consideration of recurring associations between constellations of technologies that mark genuine, demonstrable divisions in the data It should be noted at the outset that the terms such as ‘MSA’ and ‘LSA’ have been extensively criticised for failing to fully capture the variation found in the African lithic record, for imposing discrete, rigid categorical boundaries on continuous phenomena, and for artificially homogenising material within chronological or technological ‘blocks’ [17,18,19]. The LSA first appears in eastern Africa ~67ka at the site of Panga ya Saidi, where significant changes in artefact size and patterns of raw material use accompany an increasing focus on bipolar technologies, alongside alternating appearances of blade and Levallois methods, and continue to be used into the Holocene [1]. Since ANNs are necessarily stochastic (initial weights and biases and allocation to training, test, and validation sets are random), averaging across a large sample of networks trained to solve a given problem provides greater robusticity and confidence in the generated results
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