Simulating Symbolic Evolution in the Lab: Potentials and Implications of Using Transmission Chains to Study Early Symbolic Behaviour at the Emergence of Homo sapiens.

Engraved ochres and ostrich eggshells from the South African Blombos Cave and Diepkloof Rock Shelter are among the earliest expressions of human symbolic behavior. They appear to document a continuous practice of mark-making across ~40.000 years. During this time, the engraved markings change from simpler unstructured patterns to more complex markings such as cross-hatchings. Previous work examining the cognitive implications of these changes concluded that the engravings were likely used as decorations and may have served as group identity markers but not as denotational symbols. To inform discussions of the emergence of symbolic behavior, we conducted a two-part experimental study inspired by these engravings and based on the assumption that artifact use will motivate incremental adaptive refinements. Part 1 combined a delayed reproduction task with a transmission chain design to simulate an enduring mark-making practice. Eleven transmission chains were seeded with four drawings derived from the early Blombos and Diepkloof engravings and reproduced over eight generations. Transmission chain drawings showed a tendency to become increasingly regular, organized, and symmetric. Part 2 subjected a sample of the transmission chain drawings to a suite of psychophysical experiments to assess the cognitive implications of the accumulated structural changes. We found that the drawings became easier to discriminate, looked more like they had been intentionally made, and became easier to remember and reproduce, but there was no evidence of a systematic change in saliency or stylistic properties. Finally, we compared the results from the transmission chains with a similar analysis of the drawings derived from the original engravings. Although we observe interesting qualitative similarities between the original engravings and the experimental drawings, our findings suggest that cognitive biases and working memory constraints are not sufficient to generate the patterns observed in the archaeological record, highlighting the significance of social and functional contexts in shaping early symbolic artifacts. By integrating archaeological and experimental research we can better inform inferences on sparse records of early symbolic behavior. Our study thus leads to a broader consideration of the role, strengths and potential limitations of the transmission chain approach in analyzing trajectories of early symbolic behavior.