C. F. Hockett, in Animal Sounds and Communication, W. E. Lanyon and W. N. Tavolga, Eds. (American Institute of Biological Sciences, Washington, DC, 1960), pp. 392-430.

Babbling occurs during the period of roughly 7 to 12 months of age.

B. L. Davis and P. F. MacNeilage, J. Speech Hearing Res. 38, 1199 (1995) .

First (single) words are produced during the period of roughly 12 to 18 months of age.

B. L. Davis, P. F. MacNeilage, C. L. Matyear, in preparation.

A preliminary report (7) on 4 of the 10 subjects in (5) shows similar results to those found for the larger group.

P. F. MacNeilage, B. L. Davis, C. L. Matyear, Speech Comm. 22, 269 (1997) .

B. L. Davis, P. F. MacNeilage, C. Gildersleeve-Neumann, E. Teixera, paper presented at the 20th Annual Child Phonology Conference, Bangor, UK, 5 July 1999.

C. Gildersleeve, thesis, University of Texas, in preparation.

E. Teixera and B. L. Davis, in preparation.

Four other studies (12-15) often confirm our results but also show a number of counterexamples and null findings, many of which may be a result of methodological factors. [This issue is discussed in (26).]

M. M. Vihman, in Phonological Development: Models, Research, Implications, C. Ferguson, L. Menn, C. Stoel-Gammon, Eds. (York, Timonium, MD, 1992), pp. 393-422.

B. de Boysson-Bardies, in Developmental Neurocognition: Speech and Face Processing in the First Year of Life, B. de Boysson-Bardies, S. de Schonen, P. Jusczyk, P. F. MacNeilage, J. Morton, Eds. (Kluwer Academic, Dordrecht, Netherlands, 1993), pp. 353-364.

D. K. Oller and M. L. Steffans, in First and Second Language Phonology, M. Yavas, Ed. (Singular, San Diego, CA, 1993), pp. 45-62.

A. A. Tyler and T. E. Langsdale, First Lang. 16, 159 (1996) .

J. L. Locke, Phonological Acquisition and Change (Academic Press, New York, 1993).

P. F. MacNeilage and B. L. Davis, in The Evolutionary Emergence of Language, J. R. Hurford, C. Knight, M. G. Studdert-Kennedy, Eds. (Cambridge Univ. Press, Cambridge, in press).

The term "fronting," coined by Ingram (19), refers to the tendency for the first consonant in the word to have a more anterior place of articulation than the second.

D. Ingram, J. Child Lang. 1, 49 (1974) .

M. Macken, Lingua 44, 219 (1987) .

P. F. MacNeilage, B. L. Davis, A. Kinney, C. L. Matyear, Psych. Sci. 10, 459 (1999) .

P. F. MacNeilage, Behav. Brain Sci. 21, 499 (1998) .

According to frame/content theory, mandibular cyclicity may have evolved from ingestive processes (chewing, sucking, licking) through visuofacial communicative gestures (e.g., lip-smacks), common in other primates, before being paired with vocal-fold vibrations to form protosyllables.

M. Kenstowicz, Phonology in Generative Grammar (Blackwell, Oxford, 1994).

B. de Boysson-Bardies et al., in Phonological Development: Models, Research, Implications, C. Ferguson, L. Menn, C. Stoel-Gammon, Eds. (York, Timonium, MD, 1992), pp. 369-392.

P. F. MacNeilage, B. L. Davis, A. Kinney, C. L. Matyear, Child Dev. 71, 153 (2000).

J. L. Locke and D. Pearson, J. Child Lang. 17, 1 (1990).

G. E. Loeb, in Encyclopedia of Neuroscience, G. Adelman, Ed. (Birkhäer, Boston, 1987), pp. 690-692.

H. H. Kornhuber, in Encyclopedia of Neuroscience, G. Adelman, Ed. (Birkhäer, Boston, 1987), pp. 1302-1303.

A "self-organizing system" is defined by Clark (31) as "one in which some kind of higher level pattern emerges from the interactions of multiple simple components without the benefit of a leader, controller or orchestrator" (p. 73).

A. Clark, Being There: Putting Brain Body and World Together Again (MIT Press, Cambridge, MA, 1997).

P. F. MacNeilage and B. L. Davis, in Developmental Neurocognition: Speech and Face Processing in the First Year of Life, B. de Boysson-Bardies, S. de Schonen, P. Jusczyk, P. F. MacNeilage, J. Morton, Eds. (Kluwer Academic, Dordrecht, Netherlands, 1993), pp. 123-137.

T. Janson, Phonology Yearb. 3, 179 (1986) .

I. Maddieson and K. Precoda, Phonology 9, 45 (1992) .

J. D. Bengtson and M. Ruhlen, in (36), pp. 277-336.

M. Ruhlen, Ed., On the Origin of Languages: Studies in Linguistic Taxonomy (Stanford Univ. Press, Stanford, CA, 1994).

"The set of all related cognates for an individual word in different languages is known as the etymology for that word" [(36), p. 43].

"If, then, we find a mass of resemblances between different languages, resemblances that are not onomatopoetic in nature and do not appear to be borrowings, we must conclude that the similarities are a result of common origin, followed by descent with modification in the daughter languages" [(36), p. 43].

"Multilateral comparison" is comparison of sound-meaning relationships in the basic vocabularies of large sets of existing languages.

J. H. Greenberg, The Languages of Africa (Indiana Univ. Press, Bloomington, IN, 1963).

___, Language in the Americas (Stanford Univ. Press, Stanford, CA, 1987).

R. M. W. Dixon, The Languages of Australia (Cambridge Univ. Press, Cambridge, 1980).

"Generally languages change at such a rate that after more than about three or four thousand years of separation, genetic links are no longer recognizable" [(42), p. 237].

I. Goddard, Curr. Anthropol. 28, 657 (1987) .

N. Chomsky, Language and the Problems of Knowledge: The Managua Lectures (MIT Press, Cambridge, MA, 1968).

For many years, the accepted view [e.g., (45)] was that true speech became possible not because of organizational changes but because the evolution of a two-tube vocal tract made enough sounds available to produce a full language. In particular, the capacity to produce the three "point vowels" (those in "beet," "boot," and "box") has been considered criterial for a full speech capacity. But computer modeling studies have now shown (48) that the one-tubed vocal tract of a newborn infant is capable of producing the point vowels. The criterion for whether the model produces the point vowels is perceptual. We have heard a recording of the output of the model and concur that it does. The one-tubed vocal tracts of monkeys have shapes similar to that of the newborn infant, implying that they too are anatomically capable of making the point vowels.

P. H. Lieberman, D. H. Klatt, W. H. Wilson, Science 164, 1185 (1969).

L. J. Boe, Proceedings of the Fourteenth International Congress of Phonetics (San Francisco, CA, 2 to 6 August, 1999), p. 2501.