Abstract
Archaeologists interested in explaining changes in artifact morphology over long time periods have found it useful to create models in which the only source of change is random and unintentional copying error, or ‘cultural mutation’. These models can be used as null hypotheses against which to detect non-random processes such as cultural selection or biased transmission. One proposed cultural mutation model is the accumulated copying error model, where individuals attempt to copy the size of another individual's artifact exactly but make small random errors due to physiological limits on the accuracy of their perception. Here, we first derive the model within an explicit mathematical framework, generating the predictions that multiple independently-evolving artifact chains should diverge over time such that their between-chain variance increases while the mean artifact size remains constant. We then present the first experimental test of this model in which 200 participants, split into 20 transmission chains, were asked to faithfully copy the size of the previous participant's handaxe image on an iPad. The experimental findings supported the model's prediction that between-chain variance should increase over time and did so in a manner quantitatively in line with the model. However, when the initial size of the image that the participants resized was larger than the size of the image they were copying, subjects tended to increase the size of the image, resulting in the mean size increasing rather than staying constant. This suggests that items of material culture formed by reductive vs. additive processes may mutate differently when individuals attempt to replicate faithfully the size of previously-produced artifacts. Finally, we show that a dataset of 2601 Acheulean handaxes shows less variation than predicted given our empirically measured copying error variance, suggesting that other processes counteracted the variation in handaxe size generated by perceptual cultural mutation.
Highlights
The idea that human culture – defined here as socially transmitted information such as beliefs, knowledge, skills, artifact designs, and customs – constitutes an evolutionary process was hinted at by Darwin himself in The Descent of Man, where he suggested that languages evolve over time in a manner analogous to the diversification and extinction of biological species [1]
The aim of this study was to provide the first explicit experimental test of the accumulated copying error model of cultural transmission, in which artifact variation increases due to imperceptible differences between a copy of an artifact and the original copied artifact
Acheulean handaxe images were transmitted along 20 independent chains each containing 10 participants, allowing us to measure inter-individual variation in copying error (s2) which has previously only been assumed from the psychophysics literature, in which transmission error and artifact evolution are not the focus of study
Summary
The idea that human culture – defined here as socially transmitted information such as beliefs, knowledge, skills, artifact designs, and customs – constitutes an evolutionary process was hinted at by Darwin himself in The Descent of Man, where he suggested that languages evolve over time in a manner analogous to the diversification and extinction of biological species [1]. Our focus here is on the application of these cultural evolutionary methods and concepts to archaeology [11,12], which can be seen as the ‘cultural equivalent’ of paleobiology in its aims to document and explain past evolutionary change [13] This has included the use of phylogenetic methods to reconstruct historical relationships between artifacts [14], the use of models originally developed in population genetics, such as serial founder effect and neutral drift models, to explore the effects of demography on artifact variation [15,16,17,18,19,20,21,22,23,24], and the explanation of artifact variation in terms of cultural transmission biases such as prestige bias or conformity [21,25]. Note that this process will take place regardless of whether any other cultural evolutionary forces are at work, and it may be useful to incorporate this model of mutation in other, more complicated models
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