Simultaneous development of vocal and physical object combinations by a Grey parrot (Psittacus erithacus): bottle caps, lids, and labels.

On the basis of primarily behavioral data, researchers (e.g., P. M. Greenfield, 1991) have argued (a) that parallel development of communicative and physical object (manual) combinatorial abilities exists in young children; (b) that these abilities initially have a common neural substrate; (c) that a homologous substrate in great apes allows for similar, if limited, parallel development of these 2 abilities; and (d) that such abilities thus may indicate a shared evolutionary history for both communicative and physical behavior (J. Johnson-Pynn, D. M. Fragaszy, E. M. Hirsh, K. E. Brakke, & P. M. Greenfield, 1999). The authors of the present study found a comparable, if limited, parallel combinatorial development in a Grey parrot (Psittacus erithacus). Given the evolutionary distance between parrots and primates, the authors suggest that the search for and arguments concerning responsible substrates and common behavior should be approached with care and should not be restricted to the primate line.