ABSTRACT
One of the many effects of human auto-domestication is the reduction in brain volume, one of the expressions of the domestication syndrome. That atrophy happens to coincide with a time of rapidly increasing demands on this brain during the early Upper Palaeolithic. How it was compensated for has remained enigmatic so far, but the unprecedented rise of exograms in precisely that period provides a realistic explanation. Selection for the ability to work with memory traces external to the brain mitigated the need for ever more brain tissue. The nature and manifestations of exograms on the archaeological record are explained in some detail, particularly evidence for language and palaeoart. Like the persistent use of any reference system, sustained exogram use changed the structure, chemistry and operation of the human brain. Competence in employing exograms became a defining selection criterion of human modernity. Ultimately, the linkage they were capable of providing between the brain and the external world rendered the formulation and development of constructs of reality possible.
