Lipkind et al. compare the development of vocal units and sound sequences in sound production in human infants and songbirds. Early in development, infant as well as songbird vocalizations vary along continuous acoustic parameters, with discrete vocal categories and structured vocalizations only emerging later on. This emergence process shows remarkable similarities between infants and zebra finches. Contrary to earlier views, Lipkind et al. suggest that the early development of songbird song (subsong) is more comparable to the phonation stage in infants (...) than to babbling. (shrink)