The study traced the development of coordinated singing in a newly formed male-female siamang pair. Forty-five song bouts were observed during 18 wk following the pairs' initial introduction to one another. Of particular interest was the development of vocal coordination between pair members in the great-call sequence of the duet. The percentage of successfully completed great-call sequences rose from 24% for the first three sessions to 79% for the last three sessions. Types of "errors" that led to incomplete great calls were identified. The two most common errors were: uninvited female high-bark series, which accounted for the premature termination of 30% of the great-call attempts during the first three sessions and of 1 I % of the attempts during the last three sessions, and a premature male ululating scream and/or locomotion call, which accounted for the premature termination of 34% of the great-call attempts during the first three sessions and of 5% of the attempts during the final three sessions. The fully coordinated great-call sequences that finally developed closely resembled the siamang great-call sequence described by Haimoff (Behaviour 76: 128-15 1, 198 1 ; Semiotica 68: 1988). The role of experience in the development of vocal coordination is discussed.

The aim of this article is to bring clarity and unification to the question of how certain complex behaviors, such as feeding, learning, language, culture, and neural complexity, are related. Three critical ideas—the organizing principle of integrative levels, the tendency for increased complexity with evolutionary change, and the contextual nature of behavioral events—are central to the discussion. A theoretical framework is presented that synthesizes existing knowledge in a meaningful way. Data are drawn from the behavioral, neuroanatomical, cognitive, and linguistic sciences and integrated within an organized and unified theoretical perspective referred to as developmental dynamic systems theory.

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The study demonstrated the effectiveness of tape-recorded answering calls as reinforcers of vocal behavior in a female agile gibbon. Following baseline, typical conditioning, extinction, and reconditioning effects were demonstrated. The findings support the proposition that many species-typical behaviors may act as reinforcers.