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Vocal-fold stability—The question of whether vocal- fold response characteristics changed over the course of hominin evolution has broader potential implications than one might first imagine. For example, available comparative data indicate that vocal-fold composition can vary across pri- mates and it furthermore appears that developmental modi- fications known to occur in humans are correlated with changes in acoustic output. Combining these two kinds of information can help illuminate relationships between vocal- fold morphology and how vocalizations were being used, thereby shedding new light on the adaptive changes occur- ring in hominins. The specific suggestion made here is that vocal action became more stable, especially in adults. This change would be natural to connect to increasing reliance on vowel-like sounds, for instance in association with the evolu- tion of speech. However, greater vocal-fold stability may have emerged earlier to facilitate indexical cuing in the context of increasingly complex hominin social groups and relation- ships. While not directly connected to the emergence of speech, such changes may have helped set the stage for this development. Detailed knowledge of the relationship between vocal-fold structure and communicative function could be key in resolving such questions. Indexical and phonetic cuing—A final note concerns the interplay of indexical and phonetic cuing. Historically, speech scientists have struggled to separate the two in seek- ing to find invariant physical features that distinguish indi- vidual phonemes in the face of the acoustical variability occurring across talkers (as well as other factors). The upshot has been that cues to the phonetic content of speech may not exist independently of a given talker’s personal, vocal characteristics. This conflation of the phonetic and indexical is understandable in that both flow simultaneous- ly from the same source and filter system during speech. If so, however, then understanding phonetic cuing requires getting a handle on indexical cuing as well—which in turn brings the evolutionary perspective into the picture. In a sense, sexual selection effects in the voice have already had a notable effect on how phonetic features are understood. In the early years of modern acoustic phonetics, researchers focused mainly on adult male talkers, importantly because their speech revealed prominent and easily measured for- mants. Formant measurement was notably more difficult in speech from adult females or children, so much so that some came to consider the sound-spectrographic technolo- gy being used to be inherently “sexist.” There is some truth to that charge, particularly as it was later found that female speech is actually the more intelligible. As discussed earlier, finding prominent, well-defined formants in males versus other talkers is straightforwardly due to the forces of sexual selection lengthening their vocal folds and supralaryngeal vocal tracts. One can only wonder if history might have unfolded differently in the study of speech had the role of evolutionary forces on the voice itself been realized from the beginning.AT References Apicella, C. L., and Feinberg, D. R. (2009). “Voice pitch alters mate- choice-relevant perception in hunter–gatherers,” Proc. Royal Soc. B 276, 1077–1082. Apicella, C. L., Feinberg, D. R., and Marlowe, F. W. (2007). “Voice pitch predicts reproductive success in male hunter–gatherers,” Biology Lett. 3, 682–684. Bachorowski, J.-A., and Owren, M. J. (1999). “Acoustic correlates of talker sex and individual talker identity are present in a short vowel segment produced in running speech,” J. Acoust. Soc. Am. 106, 1054–1063. Binenda-Emonds, O. R. P., Cardillo, M., Jones, K. E., MacPhee, R. D. E., Beck, R. M. D., Grenyer, R., Price, S. A., Vos, R. A., Gittleman, J. L., and Purvis, A. (2007). “The delayed rise of pres- ent-day mammals,” Nature 446, 507–512. Boyd, R., and Silk, J. (2011). How Humans Evolved (W. W. Norton, New York). Bradbury, J. W., and Vehrencamp, S. L. (2011). Principles of Animal Communication (Sinauer Associates, New York). Brown, C. H., Alipour, F., Berry, D. A., and Montequin, D. (2003). “Laryngeal biomechanics and vocal communication in the squirrel monkey (Saimiri boliviensis),” J. Acoust. Soc. Am. 113, 2114–2126. Bruckert, L., Liénard, J.-S., Lacrois, A., Kreutzer, M., and Leboucher, G. (2006). “Women use voice parameters to assess men’s charac- teristics,” Proc. Royal Soc. B 273, 83–89. Brudzynski, S. (editor) (2010), Handbook of Mammalian Vocalization, Volume 19: An Integrative Neuroscience Approach (Elsever Science, Oxford, UK). Bryant, G. A., and Haselton, M. G. (2009). “Vocal cues of ovulation in human females,” Current Biol. 5, 12–15. Chiba, T., and Kajiyama, J. (1941). The Vowel: Its Nature and Structure (Tokyo: Tokyo-Kaiseikan). Coleman, R. O. (1976). “A comparison of the contributions of two voice quality characteristics to the perception of maleness and femaleness of the voice,” J. Speech and Hearing Res. 19, 168–180. Collins S. (2000). “Men’s voices and women’s choices,” Animal Behaviour 60, 773–780. Dabbs, Jr. J. M., and Mallinger, A. (1999). “High testosterone levels predict low voice pitch among men,” Personality and Individual Differences 27, 801–804. Davila Ross, M., Owren, M. J., and Zimmermann, E. (2009). “Reconstructing the phylogeny of laughter in great apes and humans,” Current Biol. 19, 1106–1111. Dixson, A. F. (2009). Sexual Selection and the Origins of Human Mating Systems (Oxford University Press, New York). Evans, S., Neave, N., Wakelin, D., and Hamilton, C. (2008). “The relationship between testosterone and vocal frequencies in human males,” Physiology & Behavior 93, 783–788. Ey, E., Pfefferle, D., and Fischer, J. (2007). “Do age- and sex-related variations reliably reflect body size in non-human primate vocalizations? A review,” Primates 48, 253–267. Fant, G. (1960). Acoustic Theory of Speech Production (Mouton, The Hague). Feinberg, D. R. (2008). “Are human faces and voices ornaments sig- naling common underlying cues,” Evolutionary Anthropol. 17, 112–118. Human Voice in Evolutionary Perspective 31