Storage of symbolic information outside the human brain is accepted here as the first undisputed evidence for cultural modernity. In the hunter-gatherer context of the Stone Age this storage could include artwork, rapidly changing artefact styles and organized spatial layout of campsites. Modern human behaviour in this context is distinguished by a symbolic use of space and material culture to define social relationships, including significant groupings based on attributes such as kinship, gender, age or skill. Symbolism maintains, negotiates, legitimizes and transmits such relationships. It is argued here that artefacts are not inherently imbued with symbolism and that modern human culture cannot be automatically inferred from inventories of archaeologically recovered material culture. Evidence for the out-of-brain storage of symbolism in southern African sites first appears in the final phase of the Middle Stone Age at about 40,000 years ago.