Using neoPiagetian theory of mental attention (or working memory), I task-analyze two complex performances of great apes and one symbolic performance (funeral burials) of early Homo
sapiens. Relating results to brain size growth data, I derive estimates of mental attention for great apes, Homo
erectus, Neanderthals, and modern Homo
sapiens, and use children's cognitive development as reference. This heuristic model seems consistent with research.