Representation and recursion in the archaeological record

Living humans are unique among the animal kingdom with respect to their ability to externalize mental representations outside the brain through a variety of media and in a recursive or creative manner (i.e., generating a potentially infinite array of combinations). Earlier humans evolved two specialized organs-the hand and the vocal tract-as primary instruments for externalizing artificial or semantic representations. These organs and the externalized representations may have coevolved with the Homo brain. The archaeological record yields examples of simple representations by 1.6 mya. More complex, hierarchical, and recursive forms are evident by roughly 0.25 mya. Complex and highly recursive representations in a wide range of media ( including representations of representations in the form of visual art) emerge after 0.1 mya among anatomically modern humans.