Abstract:

Geometric engravings are among the earliest candidates for symbolic and aesthetic expression in human evolution. The oldest known example is an intriguing set of parallel lines and zig-zags etched into a freshwater mussel shell found in Java, dated to ~500,000 years ago, while there are numerous more recent examples from all over the world, featuring common re-occurring motifs including parallel lines, zig-zags and grids. However, the role of deliberate human action in many purported palaeolithic engravings remains controversial. For example, while the discoverers of geometric markings in the Rising Star cave system argue that they were created deliberately by Homo naledi, critics argue that they are the result of natural weathering processes. Other examples of apparently deliberate engravings may be in fact a by-product of more utilitarian actions such as butchery. Ambiguous cases of palaeolithic engravings are currently challenging to resolve as there is no standardised framework for estimating the probability that particular line configurations are the result of intentional, natural or incidental processes. Here we outline a simple Bayesian probabilistic framework to address this issue and apply it to a set of test cases. To estimate the probability of intentional creation, we measure geometric properties of test cases and compare them to those of a diverse sample of Palaeolithic and Holocene engravings whose intentional origin is not in doubt. To estimate the probability of natural origin, we compare geometric properties of test cases with those of an appropriate sample of natural formations. Finally, to estimate the probability of incidental origin, we compare geometric properties of test cases with those of simulated random line configurations. Data collection and methodological refinements are still ongoing; we will present preliminary findings for discussion and feedback at the CES conference.

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