Sexual dimorphism in the structure of the human larynx is associated with differences in vocal pitch between the sexes, and these in turn have been shown to influence attractiveness to the opposite sex and perceptions of dominance. The non-human primates present a rich array of specializations of the vocal tract, including the laryngeal sacs and hyoid as well as the cartilages of the larynx. These specializations are related to sex differences in the production of sound for long-distance communication, and to differences in the mating systems of various monkeys and apes. The greatest sex differences in vocal tract anatomy occur in polygynous anthropoids, and the least dimorphism is apparent in monogamous forms. Thus although complex vocal anatomy occurs in some monogamous species (such as the siamang), it is present in both sexes in such cases, rather than being more highly developed in adult males. A preliminary comparative analysis places Homo sapiens among the polyg-ynous primates, as regards the degree of sexual dimorphism of the vocal apparatus. These findings strengthen the conclusion that polygyny played a significant role in human ancestry, perhaps among those australopithecines which ultimately gave rise to the genus Homo.

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