Chapters 2 to 6 of this book have been devoted to understanding how hearing infants increasingly develop vocal control over the first six years of their lives. The process appears to take a crucial step when babbling begins. Reduplicated babbling refers to the alternating depression and elevation of the mandible, with points of oral contacts, while phonating. To the ear, this activity produces syllabic elements that sound like speaking. In fact, though early researchers claimed that babbling and speaking were clearly separated in time, no support for this claim has emerged; indeed, there is now considerable evidence that babbling typically merges with and continues well beyond the beginning of speaking. For example, Locke (1986) listed five characteristics that are similar for babbling and speaking in the domain of consonant development: (1) singletons outnumber clusters; (2) prevocalic exceed postvocalic consonants; (3) stops, nasals and glides exceed fricatives, affricatives and liquids; (4) prevocalic stops are apical and unaspirated, rather than dorsal or aspirated; and (5) final obstruents are voiceless and either velar or glottal. These similarities fed the assumption that babbling is a real precursor of speech. However, subsequent research has revealed divergent individual heterogeneity in other acoustic parameters of speaking at the beginning of meaningful speech, such as the diversity of segments used in words. A similar phenomenon has also been revealed in early language development in the manual mode.